11 building extraction

1INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATIONExtraction of 3D building models from airborne laser scanning dataGeorge VosselmanINTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATIONBuilding model reconstructionModel, data and mapdriven approaches

3D city modellingModelling required for󰂃accuracy improvement󰂃data reduction

Christo’swrapped Reichstag

Building reconstruction from laser data󰂃Reliable 3D coordinates󰂃High point density required󰂃Assumptions on building shapes needed󰂃Usage of building ground plans

Case studies󰂃Model based approach using moments󰂃Data driven approach󰂃Map guided reconstruction󰂃Data driven󰂃Model driven

Model based approach using invariant momentsInvariance of󰂃shift󰂃scale󰂃rotation

Irregularly distributed point data∑

=⋅⋅=nPPPPPHjPiXijYM

1

󰂃7 building parameters for gable roof

󰂃1stand 2ndorder invariant moments as a function of building parameters

󰂃solve equation system (express building parameters as function of moments)

LX

LY

αΘ(X0,Y0)

H

Building reconstruction using moments2

Building reconstruction using moments󰂃segmented point cloud (X,Y,H)I

󰂃binarized moments mij

(with H = 1) for ground

plan, position and orientation

󰂃height-weighted moments Mijfor roof model model

Data-driven model refinement󰂃Detection of regions with outliers󰂃Generation of refining hypotheses

Modelling of dorms -examplePotential:󰂃minimum of 8-10 points per dorm needed

󰂃dorms must be smaller than ~40% of roof surface

Point densitySimulations with reduced point densitiesRMS derivations to parameters from high density

pts/m2centroid Θlengthwidthheightslope2.60.030.010.20.090.030.030.31.30.100.060.40.190.080.040.50.650.230.141.00.280.160.071.50.330.400.201.90.570.200.193.20.170.950.392.90.850.500.416.90.081.320.616.01.130.680.7312.1

Data driven approachAssumptions:󰂃Roof described by planar faces󰂃Height jump edges parallel or perpendicular to main building orientation

Steps:󰂃Plane detection󰂃Initial face outlining in TIN󰂃Reconstruction of building outline󰂃Reconstruction of roof face edges

Initial roof facesHeight data

Rough face outlinesConnectedcomponents3

Reconstruction of roof outlineUnion of facesApproximation by straight lines󰂃main building direction󰂃minimum edge size󰂃most pointsinsidebuildingReconstruction of face edges󰂃Ridges and valleysIntersection of planes of adjacent roof faces󰂃Roof outlineIntersection of planes with adjacent walls󰂃Height jumps inside roof surfaceStraight lines aligned to main building directions

Reconstruction of 3D building󰂃Merging edges to faces󰂃Joining parallel edges󰂃Intersection of other edges󰂃Extraction of terrain height

Using ground plansBenefits:󰂃Easy building location problem

󰂃Map and data inaccuracy󰂃Roof extensions

󰂃Constraints on roof plane orientations

󰂃Indication of building composition

Decomposition of ground plansGround planDecompositionsBuildingprimitives on partitionsDecompositions of ground plans (II)Extending edge segments at concave corners4

Combining maps with laser dataProcessing steps:󰂃Ground plan refinement 󰂃Roof face reconstruction󰂃Initial 3D model 󰂃Model refinement󰂃Detection of planar facesDetection of planar faces (II)󰂃3D Hough transform in each ground plan segment

󰂃Growing and merging of initial planar faces

Refinement of ground plan segmentation󰂃One plane per segment󰂃Detection of intersection lines󰂃Detection of height jump lines󰂃Constrained to segment orientation󰂃Not near segment edgeReconstruction of roof face outlines󰂃Best fitting plane per segment󰂃Merging of segments of same plane

Difference to TINPoint cloud viewSteep roof parts near edge with few points5

Model libraryBest model per segment (flat, slanted, gable)Initial 3D modelMerge similar models in adjacent segments

Reduction of Hough transform to 2DPoint clouds projected onto wallsRefinement of 3D modelOutlier detection

Comparison to photographs