Abstract
Abstract. Recently, building outline extraction from point cloud has gained momentum in particular in the context of 3D building modelling based on a data-driven approach, which has also been our motivation. For an accurate building outline extraction from a point cloud, various factors affecting the quality should be considered. In this research, we analysed the influence of point cloud density on the quality of the extracted building outlines. The input data was a classified photogrammetric point cloud, obtained from the dense image matching of images acquired by an optical sensor mounted on the unmanned aerial vehicle (UAV). For outline extraction, we selected two procedures, namely the direct approach and the raster approach. In the direct approach, building outlines are extracted directly from the points that have been classified as buildings. First, a convex hull with the alpha algorithm is estimated, which is further generalised with the Douglas-Peucker algorithm. This is followed by the shape regularisation to ensure perpendicular angles of the outline. In the raster approach, we first rasterised the building points and then extracted the building outlines using the Hough transform. In both approaches, the result is a roof outline in a 2D plane representing the maximum extent of the building above the surface. The building outlines were extracted from point clouds with five different densities. For both approaches, the quality assessment has shown that point cloud density has an impact on the building outline extraction, especially on the completeness of the outlines.
Highlights
Georeferenced point clouds, generated from data acquired by optic or laser sensors mounted on aerial or terrestrial platforms, have become the essential source for geospatial data modelling
We have focused on the photogrammetric point cloud, which is obtained by dense image matching of highly overlapping images, acquired by the optical sensor mounted on the unmanned aerial vehicle (UAV)
The generalised processing workflow that has been used to analyse the impact of UAV photogrammetric point cloud density on the extracted building outlines is schematically presented in Figure 1, where operations are given in rectangles and data is denoted with grey shapes
Summary
Georeferenced point clouds, generated from data acquired by optic or laser sensors mounted on aerial or terrestrial platforms, have become the essential source for geospatial data modelling. We have been witnessing the advances in the development of algorithms for automatic or semi-automatic extraction of spatial entities from georeferenced point clouds with particular attention to building outline extraction (Gilani et al, 2016; Haala and Kada, 2010; Kaartinen et al, 2005; Pfeifer et al, 2007; Rottensteiner et al, 2014). For building outline extraction and 3D city modelling, a point cloud could be obtained either by airborne laser scanning (ALS) or by dense image matching using aerial images. We have focused on the photogrammetric point cloud, which is obtained by dense image matching of highly overlapping images, acquired by the optical sensor mounted on the unmanned aerial vehicle (UAV).
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