期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2004
卷号：XXXV Part B3
页码：243-248
出版社：Copernicus Publications
摘要：The data provided by LIDAR systems are presented in a dense, accurate three-dimensional form without point classification, such as buildings, trees roads, terrain, etc. The principal objective of this research is automatic terrain extraction, without prior knowledge of the DTM. The key issue is first extracting the road network, and then use it as input information to the reconstruction process of the DTM. This approach is naturally applicable to urban areas. Various methods have been developed for terrain extraction. Most frequently used is the robust method. The essence of the robust method is computing the height of measured points by means of an interpolation function based on neighbouring points, and comparing the resulting height to the measured height. P oints describing buildings will be characterized by a large positive difference versus surface points characterized either by a large negative difference or a small positive difference. To compute the new height for a certain point, a bi-dimensional interpolation function is used, whose coefficients are extracted by adjustment process in which all points within a certain computed radios around the point take part. For a function of higher order, a singularity in the coefficient matrix is possible with the resulting solution (if any) is unstable and influenced by measurement errors. Moreover, the robust method has been developed specifically for forested areas; its application to urban areas leads to erroneous classification of buildings as land and vice verse, due to the large area of buildings, particularly with complex shapes. The objective of the present research is to improve the current method, in order to obtain better results. To achieve it, we are using orthogonal polynomials, which permit the usage of interpolation functions of a polynomial kind, without restricting the polynomial degree. An attempt was made to develop a new method base on the roads net, for computing an approximate model of the terrain. For improving the extraction process, the Roads method, and the Robust method have been merged. The algorithm for terrain extraction has been applied to four urban areas which include various kinds of problematic objects such as bridges and large buildings containing open roofs etc. Based on the qualitative aspect, the results are promising.
