Airborne LIDAR can collect the point cloud data and construct the surface model of the objects on the earth.But for the production of digital elevation model（DEM） from the point cloud

the classification（filtering）

feature extraction and quality control still pose great challenges.For extraction of DEM in urban area

the segmentation of the point cloud should be carried out.In this article

a method for deriving the DTM based on slope analysis is presented.Firstly

a TIN model is constructed from the original point cloud.The slopes are calculated in the TIN model.Then the segmentation is carried out based on the slopes in the TIN.The triangular region with large slope value is deleted.After the segmentation

the region-growing processing is used to merge the small regions according to the connectivity.The part which can cover the biggest area is considered to be the road.Finally

the terrain model is generated by kriging interpolation with these points.