测绘英语课文翻译

Unit 1 The Reliability of a Survey and Errors测量误差的可靠性Since every technique of measurement is subject to unavoidable error, surveyors must be aware of all sources and types of error and how they combine. If the accuracy of a measurement is defined as the nearness of that value to its true value (a quantity we can never know) then a surveyor must ensure that the techniques he chooses will produce a result that is sufficiently accurate. He must know, therefore, how accurate he needs to be, how to achieve this accuracy and how to check that the required accuracy has been achieved.由于每个测量技术是不可避免的误差，测量员必须知道的所有误差的来源和类型，以及它们是如何结合。

如果测量的准确性，其真正的值（我们可以永远不知道的数量）的接近程度，该值被定义为，然后测量员必须确保他选择的技术将产生一个结果，是足够精确的。

因此，他必须知道他需要的精度如何，如何实现这一目标的准确性和如何检查所要求的精度已经达到。

Accuracy requiredWhen surveying to produce a plan, the accuracy required is defined by the scale of the plot, since there should be no plottable error in the survey data. A good draughtsman can plot a length to within 0.25 mm and so, if a plan of an area is required at a scale of 1/1000, i.e., 1 mm on the plan represents 1 m on the ground, the smallest plottable distance is 0.25 m. Thus, for a survey at 1/1000 scale, all the measurements must be taken such that the relative positions of any point with respect to any other must be determined to 0.25 m or better.当测量一个平面时,精度通常是根据展图比例决定的，因为在绘图中不能有测量误差。

一个好的绘图员可以在大约0.25毫米的范围内画图，假如一个地区的图纸比例尺要求是1/1000，即1毫米图上距离代表1米实地距离，那么最小的测距应该是0.25米。

因此，对于1/1000比例尺的测量，所有测量必须保证任意一点与其他任一点的相对位置不得大于0.25米。

The specifications of surveys for other purposes such as engineering works or property boundary definition might well be determined by engineering tolerances or legal standards.基于测量规范可能被用于其他目的，如工程测量或财产边界的测量将由工程限差和合法的基准决定。

Achieving the specificationTo ensure that the specification is achieved the equipment and methods must be chosen such that, not only will they collect the right sort of data, i.e., the correct combination of angles and distances, but that the data will be to the required accuracy. There are several types of error that occur and a knowledge of their importance and characteristics is essential in the understanding of the limitations of the techniques of measurement. The salient features will be stated now but further information is given in later chapters.为了确保测量符合规范，仪器和数据应按照以下要求进行，并不是只是得到正确的数据，即更正角和边的关系，从而得到的数据满足精度的要求。

在测量中有几种类型的误差，掌握它们的重要性和特性对于理解测量技术的限差是必不可少的。

本章主要讲解这些误差的主要特征，后面的章节将提供进一步的阐述。

Mistakes 粗差Blunders or mistakes are often inaccurately referred to as gross errors. Miscounting the number of tape lengths when measuring a long distance or transposing numbers when booking are two very simple, but all too common, examples of mistakes. These types of mistakes can occur at anystage of a survey, when observing, booking, computing or plotting, and they would obviously have a very damaging effect on the results if left uncorrected. However, by following strictly a well-planned observing procedure it is possible to reduce the number that occur and then independent checks at each stage should show up those that have been made. In practice, none should ever go undetected and uncorrected.错误经常不准确的理解为粗差。

当测量很长一段距离时，读错尺的读数或记录两个简单的数时颠倒它们的位置，这些都是很常见的错误例子。

这些类型的误差可以发生在测量任何阶段，当观测，记录，计算和绘图，如果不纠正这些错误，他们在结果上显然有一个非常有害的影响。

但是，通过严格周详的观测过程，可能杜绝这些错误的产生，然后在每个阶段应独立检测可以是这些错误显现出来。

在实践中，没有不可发现和不可纠正的粗差。

Systematic errors系统误差Systematic errors arise from sources which act in a similar manner on observations. The method of measurement, the instruments used and the physical conditions at the time of measurement must all be considered in this respect. Expansion of steel tapes, frequency changes in electromagnetic distance measuring (EDM) instruments and collimation in a level are just a few examples of possible sources of systematic errors.系统误差的来源于以相同的观测方式。

测量时要考虑这些方面，测量的方法、测量仪器和外界环境。

钢尺的膨胀，电磁测距仪的频率变化和水准仪的照准情况都是系统误差的可能来源。

These errors are of vital importance in activities which consist of adding together a succession of individual observations (see sections on leveling and traversing). If all the individual measurements contain the same type of systematic error, which by their nature always act in the same direction, then the total effect is the sum of them all.这些误差在由一系列独立观测（参见水准测量和导线测量部分）累加在一起组成的测量值中极为重要，如果所有的独立测量包含相同类型的系统误差，且这些系统误差总是表现出相同的性质，那么总影响是所有这些的总和。

It must be ensured that measurements are as accurate as required by removing the effects of all factors that, if neglected, would result in a significant error. The errors caused by some factors can be eliminated with the correct observing procedure and others countered by applying corrections. Systematic errors are not revealed by taking the same measurement again with the same instruments. The only way to check adequately for systematic error is to remeasure the quantity by an entirely different method using different instruments.通过消除所有因素的影响确保精度满足要求。