A simple and accurate camera calibration method

合集下载

数码相机

According to a standard definition,a digital camera is"根据标准定义，数码相机是a camera that produces digital images that can be stored in a computer,displayed on a screen and printed".一种能形成可被储存在电脑中的数码图象的相机。

这种图象可显示在屏幕上，也可以被打印。

Years ago people used to possess two different devices in order to take pictures and make videos.过去人们常常要购置两种装置来完成摄像和制作影片的要求。

The creation of digital cameras was motivatedmainly by two factors.发明数码相机背面的胶质的原因主要有两点。

First,need to spare space.第一，为了释放空间。

Second,make it more comfortable for people to do both things with higher quality results.第二，使人类做以上两件事情时达到而更有质量的结果成为可能。

The multi-functionalism of digital cameras and the combination of several devices in one make it a popular choice for a modern man.数码相机的最大实用化和集多种装置于一身的构造使得现代人掀起购买它的热潮。

For years a digital camera has been unaffordable for many families.很长一段时间里许多家庭负担不起一部数码相机。

英语作文手机的使用情况

The use of mobile phones has become an integral part of modern life,transforming the way we communicate,access information,and even entertain ourselves.Heres a detailed look at various aspects of mobile phone usage:munication:Mobile phones have revolutionized the way we communicate.They have replaced traditional landlines in many households and are the primary means of communication for a vast majority of people.Text messaging,voice calls,and video calls are all facilitated by mobile phones,allowing people to stay in touch with friends,family, and colleagues regardless of their location.2.Social Media:With the rise of social media platforms,mobile phones have become a gateway to connecting with others on a global scale.Platforms like Facebook,Instagram, Twitter,and LinkedIn are accessible through mobile apps,enabling users to share updates, photos,and videos,and to engage in conversations with others.rmation Access:Mobile phones provide instant access to a wealth of information. With search engines like Google and apps like Wikipedia,users can find answers to their questions,learn about new topics,and stay informed about current events.4.Navigation and Maps:GPS technology in mobile phones has transformed the way we navigate.Apps like Google Maps and Waze provide realtime traffic updates,directions, and even public transit information,making it easier to travel and explore new places.5.Entertainment:Mobile phones have become a primary source of entertainment.From playing games to streaming music and videos,mobile devices offer a wide range of options for users to pass the time or relax after a long day.6.Photography:The quality of mobile phone cameras has improved dramatically,making them a popular choice for capturing ers can take highresolution photos and videos,edit them,and share them instantly with their social networks.7.Ecommerce and Online Banking:Mobile phones have made it easier to shop online and manage ers can make purchases,transfer money,and check their bank balances through secure apps.8.Health and Fitness:Many people use their mobile phones to track their health and fitness.Apps like Fitbit and MyFitnessPal allow users to log their exercise,monitor their diet,and set health goals.cation:Mobile phones are increasingly being used for educational purposes.Students can access online courses,educational apps,and ebooks,making learning more flexible and accessible.10.Work and Productivity:Mobile phones have become essential tools for work.They allow for remote working,email management,scheduling,and the ability to stay connected with colleagues and clients.11.Security and Safety:Mobile phones offer various security features,such as fingerprint recognition and facial recognition,to protect user data.Additionally,they can be used in emergency situations to call for help or track a users location.12.Cultural Impact:The widespread use of mobile phones has had a significant impact on culture,influencing how we interact,share information,and even perceive the world around us.In conclusion,mobile phones have become multifunctional devices that serve a variety of purposes beyond just making calls.They have become an extension of our lives, impacting nearly every aspect of our daily routines and interactions.。

A New Method for Scheimpflug Camera Calibration

A New Method for Scheimpﬂug Camera CalibrationAritz Legarda,Alberto Izaguirre,Nestor Arana and Aitzol IturrospeElectr.,CIS DepartmentUniversity of MondragonLoramendi4,20500Mondragon,SpainEmail of presenting author:alegarda@Abstract—An easy way to achieve higher depth ofﬁeld in a camera-laser conﬁguration is to tilt the image sensor respect to the lens plane,such that the image plane,laser plane and the lens plane intersect in a unique line(Scheimpﬂug condition[1]).If something has to be measured with this kind of cameras,a proper camera calibration must be done.The usual calibration methods are not valid in this case because they are based on the pin-hole camera model,this model being valid only for normal cameras, i.e.cameras that have the image plane and the lens plane parallel. Thus,a new camera model and its respective calibration must be developed,which includes the Scheimplug angle in the intrinsic camera parameters.In this article,the new camera model and its calibration are deﬁned.Experimental results indicate that using this calibration cameras under Scheimpﬂug condition can be accurately calibrated.I.I NTRODUCTIONStructured light techniques are very common in measure-ment systems due to its accuracy and velocity.It is one of many techniques[2]for generating dense three-dimensional (3D)surface information.When large parts need to be mea-sured,a camera with large depth of view is needed,(in Figure(I)a piece of tilted paper is observed by a normal camera;only the central part being in focus).There are some ways to increase the depth of view,e.g.by decreasing the aperture.However doing that,the intensity and the resolution becomes poorer[3].Another option to increase the depth of view is to use the Scheimpﬂug condition[1],that has been used in computer vision techniques for a long time[4].In this condition,the image plane is tilted several degrees with respect to the lens plane.To be able to measure parts with this kind of cameras,a proper camera calibration must be done.There are in the literature several calibration methods[5][6][7][8],but those methods can not be applied in cameras with Scheimpﬂug condition,because they are designed for usual cameras which have the image plane or CCD plane parallel to the lens plane. The article is divided in three main parts.In theﬁrst one,the new camera model is deﬁned,explaining how the Scheimpﬂug condition inﬂuences in the new camera model.In the second section,the new calibration method is described,andﬁnally the results are showed in two parts,those obtained using simulated data and those with real data.Finally the conclusions and future work are detailed.mdsJune01,2011II.C AMERA M ODELSubsection text here.The Scheimpﬂug camera model is based on the pin-hole assumption.In the latter,the imageplaneFig.1.Example of depth of view[9].is parallel to the lens plane but in the Scheimpﬂug camera model the image plane is tilted respect to the lens plane as can be seen in theﬁgure(2).The conditions of theαangle (twisting of the lens plane around the X cam axis see(3))and the laser plane should be the following:x0z0=x iz iso that 1d0+1d i=1f,[10](seeﬁgure(2)).Fig.2.Schematic depiction of the Scheimpﬂug condition,taken from[10]. In the pinhole camera model,the extrinsic parameters are the rotation matrix R and the translation vector T to change from the world plane to the camera plane,and the intrinsic parameters correspond to the focal length multiplied by the978-1-61284-398-8/11/$26.00 ©2011 IEEEpixel to milimeter factors(F x,F y),intersection of the optical axis with the image plane(Cx,Cy)and the distortion param-eters(equation(1)),where s is any real number different from zero.See later on the radial distortiondeﬁnition.Fig.3.Intersection of the point in the real world(p w)in the tilted plane and in the perpendicular plane.⎛⎝s·x pixs·y pixs⎞⎠=⎡⎣F x0c x0F y c y001⎤⎦·⎡⎣R⎛⎝x wy wz w⎞⎠+T⎤⎦(1)To this pinhole model equation(1),two extra parameters(α,β)are added.αis the angle between Y cam axis and the vvector(which can be arbitrarily chosen as the vertical directionof the tilted CCD plane),andβis the angle between the u vector(which can be arbitrarily chosen as the horizontal direction of the CCD tilted plane)and the vector X cam,seeﬁgure(3).The origins of the tilted and the perpendicular plane are thesame,as the perpendicular plane can be arbitrarily placed.Cameras under Scheimpﬂug condition have been used inSteroscopic Particle Image Velocimetry(SPIV),but in thisworks[11],[12],they consider a rotation matrix for smallangles between the perpendicular plane and the tilted plane,resulting in three degrees of freedom when only two degreesare needed.In[13]the rotation angles are small because theycorrected the tilted lens of the camera due to the weight on thelens.Another interesting work,[14],considers the inclinationof the sensor as an additional distortion,the radial distortionbeing the same as in Brown model[15].They change thetangential distortion adding a rotation matrix.This is onlyuseful for small angles.Finally[3]develops a system ofeleven linear equations in which only one Scheimpﬂug angleis included.In order to transform points from the tilted plane to theperpendicular plane(ﬁgure(3)),we have the followingscenario.The point p w=(x w,y w,z w) is a point in the world and r is a straight line which goes from the point p to the optical center o.This line crosses the tilted image plane and the perpendicular image plane.The vector u is deﬁned as u=(cosβ,0,sinβ) .That vector u lies in the plane X cam,Z cam.The other vector v is perpendicular to the u and has anαangle with the Y cam vector.Hence the vector v=(−sinα∗sinβ,cosα,sinα∗cosβ) .It is veriﬁed that u ∗v=0,(where u is the transpose to the vector u in matrix notation).In the following all transposed vectors are noted the same way.The equation of the line is:r:λ∗p w=λ∗(x w,y w,z w) (2) The projected point p per in the perpendicular plane at a distance f is:p per=(p perx,p pery,f) (3) The projected point p tilt in the tilted plane at a distance f is:p tilt=(0,0,f) +p tiltx∗u+p tilty∗v(4) From(3),(4)the straight line passing through the point p tilt intersects in the perpendicular plane:λ∗((0,0,f) +p tiltx∗u+p tilty∗v)=(5)(p perx,p pery,f) Resulting:λ=ff+p tiltx∗sinβ+p tilty∗sinα∗cosβ(6) Finally we obtain the point in the perpendicular plane (p perp)from the tilted one(p tilt):(p perx,p pery) =λ∗(p tiltx∗(cosβ,0)+p tilty∗(sinα∗cosβ,cosα) )(7) To do just the opposite transformation,i.e,to calculate the point in the tilted plane using the information in the perpendicular plane,the result can be easily derived: p tiltx=λ1∗(p perxcosβ+p pery∗tanα∗tanβ)p tilty=λ1∗p perycosα(8) Whereλ1is deﬁned as:λ1=ff−p perx∗tanβ−p pery∗tanαcosβ(9)In order to consider the lens distortion,we transformﬁrst the observed points(in the tilted plane)to the perpendicular one.For these transformed points,in the perpendicular plane, only radial distortion[15]have to be applied due to the radial symmetry of the lenses respect to their optical axis.p per x dist=p per x und+δpper x und(p per x,p per y) p per y dist=p per y und+δpper y und(p per x,p per y)(10)δp per x und (p per x,p per y )=Δp per x ·(k 1·r 2+k 2·r 4+k 3·r 6)δp per y und (p per x,p per y )=Δp per y ·(k 1·r 2+k 2·r 4+k 3·r 6)(11)r is the distance from the pixel to the principal point of the image,Δp per x =x p −x 0,Δp per y =y p −y 0.The radial distortion coefﬁcients are,k 1,k 2,k 3,where r 2=Δx 2+Δy 2.III.S CHEIMPFLUG CALIBRATIONTo perform the Scheimpﬂug calibration,one needs to cali-brate the intrinsic parameters with respect to the perpendicular plane,plus the angles αand β.In order to do so,accurate calibration dots are needed.Thus,a calibration plane with very accurate coded targets has been used,(ﬁgure (4)).The accuracy of the center of each dot is on the order of 3microns.An OpenCv program has been written,such that only the center and codes of the dots are extracted when the observed laser line does not intersect them.All other codes,that are either partially observed or that the laser line intersect them,are discarded.For example,in ﬁgure (5),a picture of the calibration plate can be seen together with the laser light of the camera,which can not be automatically switched off.Only the perfectly observed targets are calculated and the centers together with their codes stored in a ﬁle (in the ﬁgure (5)one observes that the calculated targets have ellipses drawn around them together with their code).In the same ﬁgure (5)one coded target can be better seen.From the coded images,the corresponding x,y,z values in the calibration plate are obtained andstored.Fig.4.Calibration plate with coded targets.In order to perform the calibration,several observations of the calibration plate are made at different positions and orien-tations relative to the camera.Initially homographies between each observed plate and their corresponding observation in the tilted image are calculated.We used Zhang’s [5]method to calculate initial estimation of the internal cameraparameters,Fig.5.Detected points in the calibration plate.for the tilted image ing initial approximate known values of the angles αand βcan be calculated,an initial estimation of the parameters in the perpendicular plane,see ﬁgure (6).In order to do so,we calculate:f =f /cos αCx =Cx +F x ∗sin α(12)Cy=Cy +F y ∗sin βWhere F x =f ∗nx ,F y =f ∗ny .With the initial intrinsic parameters obtained this way,all observed points are transform to the perpendicular image plane.Applying anew Zhang’s method to the latter points,in-trinsic and extrinsic parameters for each observation relative to the perpendicular plane being obtained.Finally a Levenberg-Marquart method is used with this initial approximations adding together the radial distortions.The minimization error is the distance between the point projected from the world to the perpendicular plane (taking into account the radial distor-tions),and the observed point transformed to the perpendicular plane (equation (7)).The minimization process takes around 15steps until con-vergence.The sensibility of each of the parameters in the minimization process is taken into account in order to get better estimations.IV.R ESULTSA.Simulated DataAll the calibration has been developed and tested using matlab.For the simulation a mathematical model of a pinhole camera with Scheimpﬂug angle has been developed,this camera having its own predeﬁned intrinsic parameters.10images with 25points in each image have been created to use them as calibration points;those images had been rotated and translated to reproduce a real image acquisition process.Then,those points have been projected using the mathematical camera model,to the tilted plane in pixels.Having the points emulating the real world and also the points in the tilted sensor plane being calculated with the real mathematical model,the whole process of calibration has been performed in order toFig.6.Calculation of the focal length from the tilted focal length obtain the initial values of the mathematical camera model. The results are shown in table(I).As can be seen all the parameters that had been calculated are practically equal to the initial ones.In this minimization process,the initial idealTABLE IR ESULT WITH SIMULATED CAMERA PARAMETERS.Parameter Initial values Calculated valuesf(mm)1212.000154Cx(pixels)640640.091Cy(pixels)512512.053α(degrees) 6.8 6.7954β(degrees)00.024k10.50.05000k20.20.19869αandβparameters were modiﬁed by few degrees,and the initial distortion coefﬁcients were set to zero.As it can be observed practically all parameters were obtained equal to the initial conditions with small errors,due to theﬁnal tolerance in the Levenberg-Marquart minimization.B.Real DataFor the experimental results,a camera with an adapter to add the Scheimpﬂug angle has been used.This camera is a uEye camera with a resolution of1280x1024,the adapter has approximatively6.6◦,and the focal length of the optic is approximatively12mm.The calibration dots were obtained taking different images,from different angles,of the calibra-tion plate.To take those pictures the camera was held by a mechanical arm,making it easier to move it,the calibration plate stable on a table.10images were taken,in each image the number of calibration points were different,depending on where the laser light was and how far was the camera from the calibration plate.Two calibrations had been made,theﬁrst one using only5of the10images taken,the second one with all the images.The values of the intrinsic parameters for theﬁrst trial are shown in the table(II).The mean of the re-projection errors,the error between the projection of the calibration points to the real world and the real values of those points in the world,also can be seen in the table(II). For the other experiment,the results are in the table(III).It can be seen that the average of the error in the both cases is0.0142mm in the X axis,and in the Y axis is0.0231mm.Soa precision of14μm and23μm is achieved.TABLE IIR ESULT REAL CAMERA,TAKEN5IMAGES OF THE CALIBRATION PLATE.Parameter Calculated valuesf(mm)13.7177Cx(pixels)579.49158Cy(pixels)829.783102α(degrees) 6.2639β(degrees)0.4005k1-0.03064607k2-0.34138208k3 1.26005919mean Error X0.014557020380443mean Error Y0.022069334675984max Error X0.058413346380107max Error Y0.056048363250767TABLE IIIR ESULT REAL CAMERA,TAKEN10IMAGES OF THE CALIBRATION PLATE.Parameter Calculated valuesf(mm)13.3643Cx(pixels)570.4787Cy(pixels)825.578449α(degrees) 6.3379β(degrees)0.4495k1-0.0199228k2-0.5434816k3 1.9547468mean Error X0.016534110332778mean Error Y0.018459397154140max Error X0.032914772169306max Error Y0.067803660489659The observation distance from the camera to the calibration plates were on the order of300mm.The projected errors in the image perpendicular plane corresponds to errors in the order of 0.1pixels,which are normal for Zhang’s minimization meth-ods,when relatively large ellipses are observed.In order to improve our method,better techiques for ellipse observations (e.g.Heikkil¨a’s method[6])needs to be used expecting the minimization error in pixels to drop in the order of between 0.01pixels to0.02pixels.V.C ONCLUSIONA novel method for the calibration of cameras under Scheimpﬂug conditions had been presented.This method consists on a extension of the normal pin-hole camera model where the image plane is perpendicular to the optical axis. To do it two extra parameters are added to previous intrinsic parameters,which are theαangle,(which is the angle between Y cam and v vector)and also theβangle(which is the angle between the u vector and the vector X cam,seeﬁgure(3). Both angles can be arbitrarily large,although an initial approx-imative previous knowledge of them is assumed.Only radial distortion in the perpendicular plane are necessary,due to the lens construction symmetries.The calibration method usesZhang’s calibration for theﬁrst initialization of the parameters, and an iterative non-linear Levemberg-Mardquardt,with the radial distortion initialized to zero for theﬁnal step.First the minimization in ideal conditions has bee tested, obtaining practically the same initial camera ter on,a real experiment has been performed,where a very accurate calibration plate has been used,with coded circular targets,whose location errors are on the order of3microns. The center of the observed ellipses has been calculated with a proprietary OpenCv ad-hoc program,where only the com-pletely observed codes,without laser interference,had been calculated.The obtained average errors in the re-projection in the real world are on the order of15microns which correspond to0.1pixel error in the projected image.A large part of this errors are assumed to the observation of large circle codes in the image,so we intend to use in our future work better performing calibration techniques(e.g.Heikkil¨a’s method[6]) in order to achieve better precisions.We strongly believe that this method can be very well suited to calibration of cameras in Scheimpﬂug conditions,because the real physical camera model of this type of cameras has been taken into account.Besides that,only radial distortions have to be taken into account,due to the fact that the perpendicular plane needs to be perpendicular to the optical axis by method construction.Thus this type of method could be employed for regular cameras where theαandβangles are very close to zero.Finally our present work is concentrated in the laser to camera calibration under Scheimpﬂug conditions.To do so, once need only to calculate the observation of the laser line pixels in each of the observed calibration plate image.As the homographies of each of this calibration plate have been identiﬁed together with the internal parameter,the laser points can be computed in camera coordinate system.Thus,known methods,(e.g Chen[16])can be used to calculate theﬁnal homography between the image camera plane and the laser plane.This method could also be very useful to relate different camera laser conﬁgurations among each other,as the complete camera models are well known.A CKNOWLEDGMENTThis work was supported by The RFExpert project(E!4745) which is in the Eurostars Programme,that is powered by EUREKA and the European Community.The authors also would like to thank to dataM the leaders of the project for helping on this research.R EFERENCES[1]R. E.Wheeler,“Notes of view camera geometry,”/photo/ViewCam.pdf,2003.[2]R.Jarvis,“A perspective on rangeﬁnding techniques for computer vi-sion,”IEEE Transactions on Pattern Analysis and Machine Intelligence, vol.PAMI-5,pp.122–39,1983/03/.[3]J.Li,Y.Guo,J.Zhu,X.Lin,Y.Xin,K.Duan,and Q.Tang,“Large depth-of-view portable three-dimensional laser scanner and its segmental calibration for robot vision,”Optics and Lasers in Engineering,vol.45,pp.1077–1087,2007.[Online].Available: /10.1016/j.optlaseng.2007.05.006[4]P.Besl,“Active,optical range imaging sensors,”Machine Vision andApplications,vol.1,no.2,pp.127–52,1988//.[5]Z.Zhang,“Aﬂexible new technique for camera calibration,”MicrosoftResearch,Tech.Rep.,1999.[6]J.Heikkill¨a,“Geometric camera calibration using circular controlpoints,”IEEE Trans.Pattern Anal.Mach.Intell.,vol.22,no.10,pp.1066–1077,2000.[7]R.Tsai,“A versatile camera calibration technique for high-accuracy3dmachine vision metrology using off-the-shelf tv cameras and lenses,”vol.3,no.4,pp.323–344,1987.[8] A.Izaguirre,P.Pu,and J.Summers,“A new development in cameracalibration:calibrating a pair of mobile cameras,”1985IEEE Interna-tional Conference on Robotics and Automation(Cat.No.85CH2152-7), 1984//.[9]/wiki/Scheimpﬂug principle.[10] A.Prasad and K.Jensen,“Scheimpﬂug stereocamera for particle imagevelocimetry in liquidﬂows,”Applied Optics,vol.34,pp.7092–9, 1995/10/20.[11]H.Louhichi,T.Fournel,vest,and H.Aissia,“Camera self-calibration in scheimpﬂug condition for airﬂow investigation,”Advances in Visual Computing.Second International Symposium,ISVC2006.Proceedings,Part II(Lecture Notes in Computer Science Vol.4292), pp.891–900,2006//.[12]H.Louhichi,T.Fournel,vest,and H.B.Aissia,“Self-calibrationof scheimpﬂug cameras:An easy protocol,”Measurement Science and Technology,vol.18,no.8,pp.2616–2622,2007.[Online].Available: /10.1088/0957-0233/18/8/037[13] C.Haig,C.Heipke,and M.Wiggenhagen,“Lens inclination due toinstableﬁxings detected and veriﬁed with vdi/vde2634part1,”pp.xx–yy,2006.[14]J.Wang,F.Shi,J.Zhang,and Y.Liu,“A new calibration model ofcamera lens distortion,”Pattern Recogn.,vol.41,no.2,pp.607–615, 2008.[15] D.Brown,“Decentering distortion of lenses,”vol.32,no.3,pp.444–462,1966.[16] C.Che and J.Ni,“Modeling and calibration of a structured-light op-tical cmm via skewed frame representation,”Journal of Manufacturing Science and Engineering,Transactions of the ASME,vol.118,pp.595–603,1996.。

2014年职称英语完形填空阅读理解字典版理工类

（理工类）14年完形填空第一篇Captain Cook Arrow Legend(库克船长弓箭的传说)It was a great legend while it lasted, but DNA testing has finally ended a two-century-old story of the Hawaiian arrow carved from the bone of British explorer Captain James Cook who died in the Sandwich Islands in 1779.―There is no Cook in the Australian Museum,‖ museum collection manager Jude Philip said not long ago in announcing the DNA evidence that the arrow was not made of Cook’s bone. But that will not stop the museum from continuing to display the arrow in its exhibition, ―Uncovered: Treasures of the Australian Museum,‖ which does include a feather cape presented to Cook by Hawaiian King Kalani’opu’u in 1778.Cook was one of Britain’s great explorers and is credited with discovering the ―Great So uth Land,‖now Australia, in 1770. He was clubbed to death in the Sandwich Islands, now Hawaii.The legend of Cook’s arrow began in 1824 when Hawaiian King Kamehameha on his deathbed gave the arrow to William Adams, a London surgeon and relative of Cook’s wife, saying it was made of Cook’s bone after the fatal fight with islanders.In the 1890s the arrow was given to the Australian Museum and the legend continued until it came face-to-face with science.DNA testing by laboratories in Australia and New Zealand revealed the arrow was not made of Cook’s bone but was more likely made of animal bone, said Philp.However, Cook’s fans refuse to give up hope that one Cook legend will prove true and that part of his remains will still be uncovered, as they say there is evidence not all of Cook’s body was buried at sea in 1779. ―On this occasion technology has won,‖ said Cliff Thornton, president of the Captain Cook Society, in a statement from Britain. ―But I am sure that one of these days …one of the Cook legends will prove to be true and it will happen one day.‖Avalanche and Its Safety(雪崩和安全问题) An avalanche is a sudden and rapid flow of snow, often mixed with air and water, down a mountainside. Avalanches are among the biggest dangers in the mountains for both life and property.All avalanches are caused by an over-burden of material, typically snowpack, that is too massive and unstable for the slope that supports it. Determining the critical load, the amount of over-burden which is likely to cause an avalanche, is a complex task involving the evaluation of a numberof factors.Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low risk of avalanche. Snow does not gather significantly on steep slopes; also, snow doesnot flow easily on flat slopes. Human-triggered avalanches have the greatest incidence when the snow’s angle of rest is between 35 and 45 degrees; the critical angle, the angle at which the human incidence of avalanches is greatest, is 38 degrees. The rule of thumb is : A slope that is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. Additionally, avalanche risk increases with use; that is , the more a slope is disturbed by skiers, thd more likely it is that an avalanche will occur.Due to the complexity of the subject, winter travelling in the backcountry is never 100% safe. Good avalanche safety is a continuous process, including route selection and examination of the snowpack, weather conditions, and human factors. Several well-known good habits can also reduce the risk. If local authorities issue avalanche risk reports, they should be considered and all warnings should be paid attention to. Never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they were made. Observe the terrain and note obvious avalanche paths where plants are missing or damaged. Avoid traveling below others who might trigger an avalanche.Giant Structures(巨型建筑)It is an impossible task to select the most amazing wonders of the modern world since every year more wonderful constructions appear.Here are three giant structures which are worthy of our admiration although they may have been surpassed by some more recent wonders.The Petronas Twin Tower The petronas Towers were the tallest buildings in the world when they were completed in 1999.With a height of 452 metres;the tall twin owers,like two thin pencils,dominate the city of Kuala Lumpur.At the 41 flool,the towers are linked by a bridge,symbolizing a gateway to the city.The American architect Cesar Pelli designed the skyscrapers.Constructed of high-strength concrete,the building provides around 1800 square metres of office space on every floor.And it has a shopping centre and a concert hall at the base.Other features of this impressive building include double-deckder lifts, and glass and steel sunshades.The Millau BridgeThe Millau Bridge was opened in 2004 in the Tarn Valley, in southern France. At the time it was built, it was the world’s highest bridge, reaching over 340m at the highest point. The bridge is described as one of the most amazingly beautiful bridge in the world. It was built to relieve Millau’s congestion problems. The congestion was then caused by traffic passing from Paris to Barcelona inSpain. The bridge was built to withstand the most extreme seismic and climatic conditions. Besides, it is guaranteed for 120 years!The Itaipu DamThe Itaipu hydroelectric power plant is one of the largest constructions of its kind in the world. It consists of a series of dams across the River Parana, which forms a natural border between Brazil and Paraguay. Started in 1975 and taking 16 years to complete, the construction was carried out as a joint project between the two countries. The dam is well-known for both its electricity output and its size. In 1995 it produced 78% of Paraguay’s and 25% of Brazil’s energy needs. In its construction, the amount of iron and steel used was equivalent to over 300 Eiffel Towers. It is a truly amazing wonder of engineering.Animal’s “Sixth Sense”(动物的”第六感”)A tsunami was triggered by an earthquake in the Indian Ocean in December, 2004. It killed tens of thousands of people in Asia and East Africa. Wild animals, however, seem to have escaped that terrible tsunami. This phenomenon adds weight to notions that they possess a ―sixth sense‖ for disasters, experts said.Sri Lankan wildlife officials have said the giant waves that killed over 24000 people along the Indian Ocean island’s coast cle arly missed wild beasts, with no dead animals found.―No elephants are dead, not even a dead rabbit. I think animals can sense disaster. They have a sixth sense. They know when things are happening,‖ H.D. Ratnayake, deputy director of Sri Lanka’s Wildlife Department, said about one month after the tsunami attack. The waves washed floodwaters up to 2 miles inland at Yala National Park in the ravaged southeast, Sri Lanka’s biggest wildlife reserve and home to hundreds of wild elephants and several leopards.―There has been a lot of apparent evidence about dogs barking or birds migrating before volcanic eruptions or earthquakes. But it has not been proven,‖ said Matthew van lierop, an animal behavior specialist at Johannesburg Zoo.―There have been no specific studies because you can’t really test it in a lab or field setting,‖ he told Reuters. Other authorities concurred with this assessment.―Wildlife seem to be able to pick up certain phenomenon, especially birds… there are many reports of birds detecting impending disasters,‖ said Clive Walker, who has written several books on African wildlife.Animals certainly rely on the known senses such as smell or hearing to avoid danger such as predators.The notion of an animal ―sixth sense‖ – or some other mythical power –is an enduringone which the evidence on Sri Lanka’s ravaged coast is likely to add to.The Romans saw owls as omens of impending disaster and many ancient cultures viewed elephants as sacred animals endowed with special powers or attributes.Singing Alarms Could Save the Blind(警报器救盲人)If you cannot see, you may not be able to find your way out of a burning building – and that could be fatal. A company in Leeds could change all that with directional sound alarms capalbe of guiding you to the exit.Sound Alert, a company run by the University of Leeds, is installing the alarms in a residential home for blind people in Sommerset and a resource centre for the blind in Cumbria. The alarms produce a wide range of frequencies that enable the brain to determine where the sound is coming from.Deborah Withington of Sound Alert says that the alarms use most of the frequencies that can be heard by humans. ―It is a burst of white noise that people say sounds like static on the radio,‖ she says. ―Its life-saving potential is great.‖She conducted an experiment in which people were filmed by thermal-imaging cameras trying to find their way out of a large smoke-filled room. It took them nearly four minutes to find the door without a sound alarm, but only 15 seconds with one.Withington studies how the brain processes sounds at the university. She says that the source of a wide band of frequencies can be pinpointed more easily than the source of a narrow band. Alarms based on the same concept have already been installed on emergency vehicles.The alarms will also include rising or falling frequencies to indicate whether people should go up or down stairs. They were developed with the aid of a large grant from British Nuclear Fuels.Car Thieves Could Be Stopped Remotely(远程制止偷车贼)Speeding off in a stolen car, the thief thinks he has got a great catch. But he is in a nasty surprise. The car is fitted with a remote immobilizer, and a radio signal from a control center miles away will ensure that once the thief switches the engine off, he will not be able to start it again.For now, such devices are only available for fleets of trucks and specialist vehicles used on construction sites. But remote immobilization technology could soon start to trickle down to ordinary cars, and should be available to ordinary cars in the UK in two months.The idea goes like this. A control box fitted to the car incorporates a miniature cellphone, a microprocessor and memory, and a GPS satellite positioning receiver. If the car isstolen, a coded cellphone signal will tell the unit to block the vehicle’s engine management system and prevent the engine being restarted.There are even plans for immobilizers that shut down vehicles on the move, though there are fears over the safety implications of such a system.In the UK, an array of technical fixes is already making life harder for car thieves. ―The pattern of vehicles crime has changed,‖ says Martyn Rand all of Thatcham, a security research organization based in Berkshire that is funded in part by the motor insurance industry.He says it would only take him a few minutes to teach a novice how to steal a car, using a bare minimum of tools. But only if the car is more than 10 years old.Modern cars are a far tougher proposition, as their engine management computer will not allow them to start unless they receive a unique ID code beamed out by the ignition key. In the UK, technologies like this have helped achieve a 31 per cent drop in vehicle-related crime since 1997.But determined criminals are still managing to find other ways to steal cars. Often by getting hold of the owner’s keys in a burglary. In 2000, 12 per cent of vehicles stolen in the UK were taken by using the owner’s keys, which doubles the previous year’s figure.Remote-controlled immobilization system would put a major new obstacle in the criminal’s way by making such thefts pointless.A group that includes Thatcham, the police, insurance companies and security technology firms have developed standards for a system that could go on the market sooner than the customer expects.An Intelligent Car(智能汽车)Driving needs sharp eyes, keen ears, quick brain, and coordination between hands and the brain. Many human drivers have all these and can control a fast-moving car. But how does an intelligent car control itself?There is a virtual driver in the smart car. This virtual driver has ―eyes‖, ―brains‖, ―hands‖ and ―feet‖, too. The minicameras on each side of the car are his ―eyes‖, which observe the road conditions ahead of it. They watch the traffic to the car’s left and right. There is also a highly automatic driving system in the car. It is the built-in computer, which is the virtual driver’s―brain‖. His ―brain‖ calculates the speeds of other moving cars near it and analyzes their positions. Basing on this information, it chooses the right path for the intelligent car, and gives instructions to the ―hands‖and ―feet‖ to act accordingly. In this way, the virtual driver controls his car.What is the virtual driver’s best advantage? He reacts quickly. The minicameras are sending images continuously to the ―brain.‖ Itcompletes the processing of the images within 100 milliseconds. However, the world’s best driver at least needs one second to react. Besides, when he takes action, he needs one more second.The virtual driver is really wonderful. He can reduce the accident rate considerably on expressways. In this case, can we let him have the wheel at any time and in amy place? Experts warn that we cannot do that just yet. His ability to recognize things is still limited . He can now only drive an intelligent car on expressways.Why India Needs Its Dying Vultures(印度为什么需要濒临灭亡的秃鹰)The vultures in question may look ugly and threatening, but the sudden sharp decline in three species of India’s vultures is producing alarm rather than celebration. and it presents the world with a new kind of environmental problem. The dramatic decline in vulture numbers is causing widespread disruption to people living in the Same areas as the birds. It is also causing serious public health problems across the Indian sub-continent．While4their reputation and appearance may be unpleasant to many Indians. vultures have long played a very important role in keeping towns and villages all over India clean. It is because they feed on dead cows. In India. cows are sacred animals and are traditionally left in the open when they die in their thousands upon thousands every year.The disappearance of the vultures has led to an explosion in the numbers of wild dogs feeding on the remains of these dead animals. There are fears that rabies may increase as a result．And this terrifying disease may ultimately affect humans in the region, since wild dogs are its main carriers．Rabies could also spread to other animal species, causing an even greater problem in the future．The need for action is urgent, so an emergency project has been launched to find a solution to this serious vulture problem. Scientists are trying to identify the disease causing the birds deaths and, if possible, develop a cure.Large-scale vulture deaths were first noticed at the end of the 1980s in India. A population survey at that time showed that the three species of vultures had. Declined by over 90 percent. All three species are now listed as―critically endangered‖. As most vulture lay only single eggs and take about five years to reach maturity, reversing their population decline will be a long and difficult exercise.Wonder Webs(奇妙的网)Spider webs are more than homes, and they are ingenious traps. And the world’s best web spinner may be the Golden Orb Weaver spider. The female Orb Weaver spins a web of fibers thin enough to be invisible to insect prey, yet tough enough to snare a flying birdwithout breaking.The secret of the web’s strength? A type of super-resilient silk called dragline. When the female spider is ready to weave the web’s spokes and frame, she uses her legs to draw the airy thread out through a hollow nozzle in her belly. Dragline is not sticky, so the spider can race back and forth along it to spin the web’s trademark spiral.Unlike some spiders that weave a new web every day, a Golden Orb Weaver reuses her handiwork until it falls apart, sometimes not for two years. The silky thread is five times stronger than steel by weight and absorbs the force of an impact three times better than Kevlar, a high-strength human-made material used in bullet-proof vests. And thanks to its high tensile strength, or the ability to resist breaking under the pulling force called tension, a single strand can stretch up to 40 percent longer than its original length and snap back as well as new. No human-made fiber even comes close.It is no wonder manufacturers are clamoring for spider silk. In the consumer pipeline: high-performance fabrics for athletes and stockings that never run. Think parachute cords and suspension bridge cables. A steady supply of spider silk would be worth billions of dollars – but how to produce it? Harvesting silk on spider farms does not work because the territorial arthropods have a tendency to devour their neighbors.Now, scientists at the biotechnology company Nexia are spinning artificial silk modeled after Golden Orb dragline. The first step: extract silk-making genes from the spiders. Next, implant the genes into goat egg cells. The nanny goats that grow from the eggs secrete dragline silk proteins in their milk. ―The young goats pass on the silk-making gene without any help from us,‖ says Nexia president Jeffrey Turner. Nexia is still perfecting the spinning process, but they hope artificial spider silk will soon be snagging customers as fast as the real thing snags bugs. Chicken Soup for the Soul:Comfort Food Fights Lneliness（心灵鸡汤：爽心食品排解孤独感）Mashed potatoes, macaroni and cheese, may be bad for your arteries，but according to a study in Psychological Science, they’re good for your heart and emotions．The study focu ses on ―comfort food‖ and how it makes people feel．"For me personally,food has always played a big role in my family,‖ says Jordan Troisi, a graduate student at the University of Buffalo, and lead author on the study．The study came out of the research program of his co—author Shira Gabriel．It has looked at non-human things that may affect human emotions．Some people reduce loneliness by bonding with their favorite TV show, buildingvirtual relationships with a pop song singer or looking at pictures of loved ones．Troisi and Gabriel wondered if comfort food could have the same effect by making people think of their nearest and dearest.In one experiment, in order to make participants feel lonely, the researchers had them write for six minutes about a fight with someone close to them．Others were given an emotionally neutral writing assignment. Then, some people in each group wrote about the experience of eating a comfort food and others wrote about eating a new food．Finally,the researchers had participants complete questions about their levels of loneliness．Writing about a fight with a close person made people feel lonely．But people who were generally secure in their relationships would feel less lonely by writing about a comfort food．"We have found that comfort foods are consistently associated with those close to us．"says Troisi．"Thinking about or consuming these foods later then serves as a reminder of those close others．"In their essays on comfort food, many people wrote about the experience of eating food with family and friends.In another experiment, eating chicken soup in the lab made people think more about relationships, but only if they considered chicken soup to be a comfort food．This was a question they had been asked long before the experiment, along with many other questions, so they wouldn’t remember it.Throughout everyone’s daily lives they experience stress, often associated with our connections with others," Troisi says．"Comfort food Can be an easy remedy for loneliness．Climate Change Poses Major Risks for Unprepared Cities （气候变化给不备城市带来重大风险）A new examination of urban policies has been carried out recently by Patricia Romero Lankao．She is a sociologist specializing in climate change and urban development．She warns that many of the world’s fast-growing urban areas，especially in developing countries．will likely suffer from the impacts of changing climate．Her work also concludes that most cities are failing to reduce emissions of carbon dioxide and other greenhouse gases．These gases are known to affect the atmosphere．‖Climate change is a deeply local issue and poses profound threats to the growing cities of the world,‖ says Romero Lankao. ‖But too few cities are developing effective strategies to protect their residents."Cities are major sources of greenhouse gases．And urban populations are likely to be among those most severely affected by future climate change. Lankao’s findings highlight ways in which city-residents are particularly vulnerable, andsuggest policy interventions that could offer immediate and longer-term benefits．The locations and dense construction patterns of cities often place their populations at greater risk for natural disasters. Potential threats associated with climate include storm surges and prolonged hot weather. Storm surges can flood coastal areas and prolonged hot weather can heat heavily paved cities more than surrounding areas．The impacts of such natural events can be more serious in an urban environment．For example，a prolonged heat wave can increase existing levels of air pollution，causing widespread health problems．Poorer neighborhoods that may lack basic facilities such as drinking water or a dependable network of roads，are especially vulnerable to natural disasters．Many residents in poorer countries live in substandard housing without access to reliable drinking water，roads and basic services.Local governments, therefore,should take measures to protect their residents.‖Unfortunately，they tend to move towards rhetoric rather than meaningful responses, Romero Lankao writes, ‖ They don’t impose construction standards that could reduce heating and air conditioning needs. They don't emphasize mass transit and reduce automobile use. In fact, many local governments are taking a hands—off approach.‖ Thus, she urges them to change their idle policies and to take strong steps to prevent the harmful effects of climate change on cities..Free Statins With Fast Food Could Neutralize Heart Risk (快餐加免费降胆固醇药物可以降低罹患心脏病的风险)Fast food outlets could provide statin drugs free of charge so that customers can reduce the heart disease dangers of fatty food, researchers at Imperial College London suggest in a new study．Statins reduce the amount of unhealth y ‖LDL‖ cholesterol in the blood. A wealth of trial data has proven them to be highly effective at lowering a person’s heart attack risk .In a paper published in the American Journal of Cardiology，Dr Darrel Francis and colleagues calculate that the reduction in heart attack risk offered by a statin is enough to offset the increase in heart attack risk from eating a cheeseburger and drinking a milkshake．Dr Francis，from the National Heart and Lung Institute at Imperial College London，who is the senior author of the study, said:‖Statins don’t cut out a11 of the unhealthy effects of cheeseburgers and French fries．It’s better to avoid fatty food altogether．But we’ve worked out that in terms of your possibility of having a heart attack. Taking a statin can reduce your risk to more orless the same degree as a fast food meal increases it.‖ ―It’s ironic that people are free to take as many unhealthv condiments in fast food outlets as they like, but statins, which are beneficial to heart health, have to be prescribed. It makes sense to make risk-reducing statins available just as easily as the unhealthy condiments that are provided free of charge．It would cost less than 5 pence per customer一not much different to a sachet of sugar.‖ Dr Francis said．When people engage in risky behaviours like driving or smoking, they’re encouraged to take measures that lower their risk, 1ike wearing a seatbelt or choosing cigarettes with filters. Taking a statin is a rational way of lowering some of the risks of eating a fatty meal．Better Solar Energy Systems: More Heat, More Light （更有效的太阳能系统：更多热量，更强灯光）Solar photovoltaic thermal energy systems, or PVTs, generate both heat and electricity, but until now they haven’t been very good at the heat-generating part compared to a stand-alone solar thermal collector. That’s because they operate at low temperatures to cool crystalline silicon solar cells, which lets the silicon generate more electricity but isn’t a very efficient way to gather heat.That’s a problem of economics. Good solar hot-water systems can harvest much more energy than a solar-electric system at a substantially lower cost. And it’s also a space problem: photovoltaic cells can take up all the space on the roof, leaving little room for thermal applications.In a pair of studies, Joshua Pearce, an associate professor of materials science and engineering, has devised a solution in the form of a better PVT made with a different kind of silicon. His research collaborators are Kunal Girotra from Thin Silicon in California and Michael Pathak and Stephen Harrison from Queen’s University, Canada.Most solar panels are made with crystalline silicon, but you can also make solar cells out of amorphous silicon, commonly known as thin-film silicon. They don’t create as much electricity, but they are lighter, flexible, and cheaper. And, because they require much less silicon, they have a greener footprint. Unfortunately, thin-film silicon solar cells are vulnerable to some bad-news physics in the form of the Staebler-Wronski effect.―That means that their efficiency drops when you expose them to light—pretty much the worst possible effect for a solar cell,‖ Pearce explains, which is one of the reasons thin-film solar panels make up only a small fraction of the market.However, Pearce and his team found a way to engineer around the Staebler-Wronski effect by incorporating thin-film silicon in anew type of PVT. You don’t h ave to cool down thin-film silicon to make it work. In fact, Pearce’s group discovered that by heating it to solar-thermal operating temperatures, near the boiling point of water, they could make thicker cells that largely overcame the Staebler-Wronski effect. When they applied the thin-film silicon directly to a solar thermal energy collector, they also found that by baking the cell once a day, they boosted the solar cell’s electrical efficiency by over 10 percent.Sharks Perform a Service for Earth's Waters（鲨鱼有益于地球水系）It is hard to get people to think of sharks as anything but a deadly enemy1. They are thought to attack people frequently. But these fish2 perform a valuable service for earth's waters and for human beings. Yet business and sport fishing3 are threatening their existence Some sharks are at risk of disappearing from EarthWarm weather may influence both fish and shark activity. Many fish swim near coastal areas because of their warm waters. Experts say sharks may follow the fish into the same areas, where people also swim. In fact, most sharks do not purposely charge at or bite humans. They are thought to mistake a person for a sea animal, such as a seal or sea lion. That is why people should not swim in the ocean when the sun goes down or comes up. Those are the times when sharks are looking for food. Experts also say that bright colors and shiny jewelry may cause sharks to attack.A shark has an extremely good sense of smell4' It can find small amounts of substances in water, such as blood, body liquids and chemicals produced by animals. These powerful senses help sharks fred their food. Sharks eat fish, any other sharks, and plants that live in the ocean.Medical researchers want to learn more about the shark's body defense, and immune systems against disease. Researchers know that sharks recover quickly from injuries. They study the shark in hopes of finding a way to fight human disease.Sharks are important for the world's oceans They eat injured and diseased fish. Their hunting activities mean that the numbers of other fish in ocean waters do not become too great This protects the plants and other forms of life that exist in the oceans. “Liquefaction” Key to Much of Japanese Earthquake Damage （“液化”是日本地震破坏的关键）The massive subduction zone1 earthquake in Japan caused a significant level of soil "liquefaction" that has surprised researchers with its widespread severity, a new analysis shows."We've seen localized3 examples of soil。

相机标定误差因素分析

２８2012年第1期（总第117期）2012（Sum.No117）信息通信INFORMATION&COMMUNICATIONS相机标定误差因素分析尹洪涛1，刘成1，李一兵2，鲁光泉3，刘文超2(1.装甲兵工程学院，北京100072；2.清华大学汽车安全与节能国家重点实验室，北京10084；3.北京航空航天大学汽车工程系，北京10083)摘要：分析了影响相机标定精度的一些主要因素，并给出了在这些因素影响下世界坐标重投影误差的分布曲线。

仿真及实验表明在非线性相机模型的线性标定方法中，世界坐标的测量精度对相机标定精度有较大影响，标定图片数量15-20幅较合适。

对相机标定中合理制作标定板、选择标定图片数量、快速高精度标定相机提供了有益帮助。

关键词：相机标定；误差；因素分析中图分类号：O242.2文献标识码：A文章编号：1673-1131（2012）01-0028-03Analysis of Factors on the Error of the Camera Calibration Abstract：In order to improve the accuracy of camera calibration,the factors that influence it must be considered.Some main factors are analysed comprehensively.The curves of the distribution of the error of the feature points'restructure of these factors are puter simulation and real data experiments demonstrate that in the linear calibration method of nonlinear cam-era model,the precision of the feature points'coordinates influence the calibration accuracy to a great extent;The appropriate calibrated image number is between15and20.The research may provide reference for model planes making,calibrated image number determination and efficient camera calibrating.Key words：Camera Calibration;Errors;Factor Analysis0引言标定是计算机视觉中最关键、最基本的一步，标定精度及其稳定性对机器精度影响较大。

手机作用的英语作文

The smartphone has become an indispensable part of modern life,revolutionizing the way we communicate,work,and entertain ourselves.Heres a detailed look at the various roles smartphones play in our daily lives.Communication Hub:Smartphones have transformed the way we communicate.With instant messaging apps, social media platforms,and video calling features,staying in touch with friends and family across the globe has never been easier.The integration of email and various messaging services allows for quick and efficient communication in both personal and professional contexts.Information Access:Smartphones provide instant access to a wealth of information.With search engines, news apps,and educational platforms,users can learn about current events,explore new topics,and even take online courses.The internet in the palm of your hand has made knowledge more accessible than ever before.Entertainment Device:For entertainment,smartphones offer a variety of options.From streaming music and movies to playing games,smartphones keep users engaged and entertained.They also support various forms of multimedia consumption,such as podcasts,eBooks,and audiobooks,catering to diverse tastes and preferences.Photography and Video Recording:The camera quality on smartphones has improved dramatically,making them a goto device for capturing memories.Highresolution images and advanced camera features allow users to take professionallooking photos and record videos,which can be easily edited and shared on social media.Navigation and Travel Companion:With GPS and mapping services,smartphones have become essential travel tools.They provide realtime traffic updates,public transportation schedules,and walking or driving directions.This makes it easier to navigate unfamiliar places and plan trips efficiently.Health and Fitness Tracker:Many smartphones come with builtin health and fitness tracking features.They can monitor physical activity,sleep patterns,and even heart rate,helping users maintain a healthy lifestyle.Integration with various health apps allows for more detailed tracking and goal setting.Mobile Wallet and Financial Management:Smartphones have also become a secure way to handle financial transactions.Mobile wallets and banking apps enable users to make payments,transfer money,and manage their finances on the go.This has streamlined the process of handling money and made transactions more convenient.Productivity Tool:For productivity,smartphones offer a range of applications that can help with task management,notetaking,and scheduling.They can sync with other devices,allowing users to access their work and personal files from anywhere,ensuring that they stay organized and on top of their responsibilities.Emergency and Safety:In times of need,smartphones can be a lifeline.They can call for help,provide information during emergencies,and even have features like location sharing to ensure safety.Some smartphones also have builtin emergency alerts and SOS features.Customization and Personalization:One of the appealing aspects of smartphones is their ability to be ers can personalize their devices with different apps,themes,and settings,making the smartphone experience unique to each individual.In conclusion,the smartphone is a multifaceted tool that has permeated nearly every aspect of our lives.Its versatility and convenience make it an essential companion for navigating the complexities of the modern world.。

镜头说明书

If your camera will not record video or shoot in still mode, make sure you are in either Manual or Aperture Priority exposure control mode, and that “release without lens” is enabled within your camera’s menus.• Aperture adjustment is done directly on the aperture ring of the lens, NOT from a control on your camera.• It is suggested that ISO be set manually, NOT on auto. Set it to a sensitivity appropriate for the subject, lighting conditions, and speed/aperture settings you want to utilize• Available in mounts to t all major camera brands, and o eringFull Frame coverage, it will provide high quality video and still images with Mirrorless and DSLR cameras of any sensor size.• It o ers full cine lens features including a de-clicked aperture control, industry standard 0.8 MOD focus and aperture ring gearing, a precise and smooth long focus throw, T-stop calibration, and tight color matching .• The fourteen elements in ten groups design utilizes seven specialized elements including one Aspherical, two Extra Low Dispersion, one Hybrid Aspherical, and three High Refractive Index types. UMC anti-re ective coatings are applied to all lens elements for clear and vibrant images.• Its compact size and light weight design makes it perfect for hand-held and gimbal shooting along with enhanced stability and comfortable use.• Do not look directly at the sun through the lens as it may seriously impair your vision.• Attach or detach the lens only while the camera is turned o .• Protect the lens from water, high humidity and excessive heat.• Avoid subjecting the lens to drastic temperature changes such as moving from a very cold outdoors location to a warm indoors location. This can cause moisture in the air to condense inside or on the outside of the lens and lead to failure or mold production.• Before taking the lens indoors from a cold outdoors location, put the lens in a plastic bag or sealed camera bag, and remove it only when the lens has warmed up to room temperature.135mm T2.2CINE DSXInstruction ManualThank you for purchasing the ROKINON Cine DSX 135mm T2.2Full Frame prime lens.Please read this instruction manual prior to use to familiarize yourself with functions of the lens, the operating method, and cautions.1 ) MOUNT2 ) DISTANCE SCALE INDEX3 ) DISTANCE SCALE4 ) FOCUSING RING5 ) HOOD MOUNT6 ) HOOD7 ) DEPTH OF FEILD SCALE 8 ) APERTURE INDEX 9 ) APERTURE RING• It is extremely important before cleaning to dust o the lens surface using a lens blower or a soft brush to remove any foreign particles or grit that could scratch the lens.• For stubborn spots, use only one or two small drops of a reputable lens cleaner on a micro ber cloth, and gently wipe the lens in a circular motion.DO NOT USE AN ORGANIC SOLVENT SUCH AS PAINT THINNER, ALCOHOL, OR BENZENE.• Align the index mark on the lens barrel with the index mark on the lens mount of the camera.• Do not press the lens release button on the camera when mounting the lens.• Insert the lens into the camera mount and rotate it clockwise (Counterclockwise for Nikon mounts) until it “clicks” and locks into place. Do not insert the lens at an angle.• Remove the front lens cap when you are ready to shoot.• Attach the front lens cap.• While holding down the lens release button on the camera body,rotate the lens counterclockwise (Clockwise for Nikon mounts) until it stops and separate the lens from the body.• Attach the rear lens cap.It can be di cult to achieve optimum focus using the unaided eye when focusing a telephoto lens such as a 135mm. Please checkyour camera’s instruction book for manual focusing aids. These aids can include Focus Peaking, Focus Magni cation, and Focus Con rmation. • Set the Focus Mode of your camera to Manual Focus.• Set the lens to its maximum aperture of T2.2. This enables you tocritically focus by eliminating the in uence that depth of eld provides at smaller apertures.• After achieving critical focus at T2.2, set your shooting aperture.• Precise In nity Focus NOT located at the focus stop at the in nity end of the focus scale. The exact point on the focusing scale for critical in nity focus will vary depending on camera and lens mount, wear,temperature, and normal design tolerances. Typically it will be in or near the “L” shaped area at the in nity end of the focusing scale.• Features include a 9 blade aperture for smoother bokeh, weather sealed mounts, and gears that are designed to be smoother to the touch for enhanced comfort when pulling focus by hand. The lens designation “135mm T-2.2” is marked on both sides of the lens, and the aperture and focusing scales have been improved for better visibility.FEATURES123784569- The minimum focus is the distance from the image sensor to the object.- The product speci cations and exterior are subject to change without notice.- The supported functions of this product may vary according to the camera brand and model.Notes• Front Lens Cap • Instruction Manual/ Warranty • Soft Lens Pouch• Rear Lens CapROKINON CINE DSX 135mm T2.2T2.2 ~ 222.62ft (0.8m)Ø77.09∞ to 2.62 ft11 Elements in 7 GroupsAperture RangeMount Angle of View (Full Frame / APS-C)Optical Construction Minimum Focusing DistanceFilter Size Number of Aperture Blades Focus RangeModel CANON EF18.8° / 12.6°NIKON18.8° / 12.6°SONY E18.8° / 12.6°Length Weight (121.1mm)4.76“(866.4g)1.91lb(119.6mm)4.70“(850.4g)1.87lb(148.1mm)5.23“(918.2g)2.02lb(148.4mm)5.84“(912.0g)2.01lb(146.9mm)5.78”(908.4g)2.00lbFUJI X12.6°MFT9.0°Thank you or Purchasing a Rokinon product. Rokinon lenses and accessories are renowned worldwide to deliver the performance required and exceptional value appreciated by both professional and beginner photographer/videographers.This certi cate assures that the Rokinon product model and serial number below were manufacrtured by Samyang Optics in South Korea and incorporates theirlatest technology, attention to quality and detail.Super 3513.6°。

高中英语阅读理解高频考点专项练习题(历年高频考点真题) (1694) output

一、阅读理解1. 请认真阅读下列短文，并根据所读内容在文章后表格中的空格里填入一个最恰当的单词。

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Anyone who’s ever made room for a big milestone of adult life----a job, a marriage, a move----has likely shoved a friendship to the side. After all, there is no contract locking us to the other person, as in marriage, and there are no blood bonds, as in family. We choose our friends, and our friends choose us. That’s a really distinctive attribute of friendships.But modern life can become so busy that people forget to keep choosing each other. That’s when friendships fade, and there’s reason to believe it’s happening more than ever. Loneliness is on the rise, and feeling lonely has been found to increase a person’s risk of dying early by 26%----and to be even worse for the body than obesity and air pollution. Loneliness damages health in many ways, particularly because it removes the safety net of social support. “When we perceive our world as threatening, that can be associated with an increase in heart rate and blood pressure.”The solution is simple: friendship. It helps protect the brain and body from stress, anxiety and depression. “Being around trusted others, in essence, signals safety and security,” says Holt-Lunstad. A study last year found that friendships are especially beneficial later in life. Having supportive friends in old age is a stronger predictor of well-being than family ties ----suggesting that the friends you pick may be at least as important as the family you’re born into.Easy as the fix may sound, it can be difficult to keep and make friends as an adult. But research suggests that you only need between four and five close pals. If you’ve ever had a good one, you know hat you’re looking for. “The expectations of friends, once you have a mature understanding of friendship, don’t really change across the life course,” Rawlins says. “People want their close friends to be someone they can talk to and someone they can depend upon.”If you’re trying to fill a dried-up friendship pool, start by looking inward. Think back to how you met some of your very favorite friends.V olunteering on a political campaign or in a favorite spin class? Playing in a band? “Friendships are always about something,” says Rawlins. Common passions help people bond at a personal level, and they bridge people of different ages and life experiences.Whatever you’re into, someone else is too. Let your passion guide you toward people. V olunteer, for example, take a new course or join a committee at your community centers. If you like yoga, start going to classes regularly. Fellow dog lovers tend to gather at dog runs. Using apps and social media----like Facebook to find a local book club----is also a good way to find easy-going folks.Once you meet a potential future friend, then comes the scary part: inviting them to do something. “Y ou do have to put yourself out there,” says Janice McCabe, associate professor of sociology at Dartmouth College and a friendship researcher. “There’s a chance that the person will say no. But there’s also the chance they’ll say yes, and something really great could happen.”The process takes time, and you may experience false starts. Not everyone will want to put in the effort necessary to be a good friend.It’s never too late to start being a better pal. The work you put into friendships----both new and old --- will be well worth it for your health and happiness.文章大意：本文是一篇说明文。

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k=1
k=O
Fig. 1 Setup of calibration chart and TV camera
Table 1. TV camera parameters to be calibrated
intrinsic parameters
Cu, C
extrinsic parameters
, , () lj)
A simple and accurate camera calibration method
Diii Zhang, Yoshihiko Nomura, Seizo Fujii
Faculty of Engineering Nagoya University Chikusa-ku, Nagoya, 464-01 JAPAN
R=
sin3 sine sinip + cos4 COS14) cos3 sin4
-sine
(2) Perspective relation
cos cos4
U;Jk-CU — XC
-zc
—
Vjjk-Cv
f
Z
(2.2)
(3) Radial lens distortion
+k5
where
(2.3)
r' =
L
to +ktsin8 tyo -ktsin4
tzo +
I
k tcV7os4)2 - (sin I
sine cosc cosip + sin4 sinw
sin1 cos4 sini,p - Sifl cosip
r
COS COS1
COS€ Slfl14
sine sin4 cosi.p - cos sinip
UjJk C1
By substituting Eq.2.2 into Eq.2.3, the following equations are deduced.
uji k Cu+f ÷k3f(-)2 r(X)2+ ( )21 + k5(f-)4[()2+ ()1C)2]2
Vjjk
+ +k3()3[()2+ ())21 k5()5f()2+ ())22
distortion. The point q' with the coordinates (Jk'ViJk )is the ideal image of the point Q, and is not
subjected to lens distortion. The camera parameters to be calibrated are shown in Table 1 . They are separated into the intrinsic parameters and the extrinsic parameters which depend on the relative position and orientation between the TV camera and 3-D world coordinates.
\V') =
where the unknown parameter vector X LCu,C'v,f ,k3,k5,d, , 4) , 14 ,tO,tyO,t0 J and :k(k)iS the k-th
condition.The effectiveness of the method and the optimal calibration condition are confirmed by
experiments.
2. CAMERA CALIBRATION
2.1 System Setup
The system setup is shown in Fig.1. The fiducial marks to be used in calibration are set by the following manner: (1) All the fiducial marks are drawn on a plane with uniform interval ic in the horizontal and vertical directions. We call it calibration chart . The lengths of fiducial marks from left to right and top to bottom directions are lx and 1y , respectively. Subscripts ij are defmed as the order of fiducial mark in x and y directions respectively. (2) The chart is translated in the direction of Z with a known distance of t, and subscript k is the order of the translation. The translation is necessary to get the unique solution.
txo ,Vo ,zo
2.2 Calibration Method
The transformation from 3-D world coordinates ( Xw,Yw,Zw ) to 2-D image plane coordinates
(Uij k, ViJ k ) is subdivided into the three transformations.
esti mation method, and examines the relation between calibration accuracy and calibration conditions by applying a law of error propagation. Furthermore, the optimal calibration condition is proposed and the variance of the estimated 3-D information is determined quantitatively in the case of optimal calibration
(1) Rigid body transformation
X=RX÷T
where Xc and X are the vectors of 3-D camera coordinates and 3-D world coordinates respectively.
(2.1)
140/SPIE Vol.
1822 (1992)
Downloaded from SPIE Digital Library on 11 Dec 2009 to 159.226.100.197. Terms of Use: /terms
r Xc = Yc
z
xHyw
J
rxw
=
il-1f2
LzJ L
jl-l
0
1
]
T=r
ABSTRACT
A simple and accurate camera calibration method is presented in this paper, and the relation between accuracy of calibrated TV camera parameters and calibration condition is examined by applying a law of error propagation. The optimal calibration condition is proposed where an iterative method is applied to calibrate the parameter values. Furthermore, the variance of the estimated 3-D information is determined
the arrangement of fiducial marks and so on, and what is the optimal calibration condition with the
miThis paper presents a simple and accurate camera calibration method, which uses an iterative
(2.4)
Furthermore, by substituting Eq.2. 1 into Eq.2.4, the transformation equations from the indices f' k into Ujjk and''iik are obtained for the fiducial marks, and they act as the regression equations in a least squares method. The non-linear regression equations are linearized by applying the Gauss-Newton method as follows.
quantitatively in the case of the optimal calibration condition. These results are confirmed through
experiments.
1. INTRODUCTION
Camera calibration takes very important part in 3-D measurement, recognition and robot control. It will be very useful to clarify the camera calibration accuracy since the accuracy of camera calibration will influence directly the performance of many vision and image processing tasks. Although several papers ij have reported about experimental results concerning calibration accuracy, there has not been clarified what is the relation between the calibration accuracy and its conditions such as the number of fiducial marks,