Urban building extraction is an important research topic in urban studies. We present a three-step method to detect the
outline of buildings, Firstly, DEM (Digital Elevation Model) is separate from DSM (Digital Surface Model), in our
algorithm, and surface based method is adopted. The second step is to classify buildings and other off-terrain objects.
Texture characters are selected to classify them. Four parameters (Contrast, Energy, Entropy, and Homogeneity) are
defined to describe textures. Rough set method is used to distinguish between buildings and non-buildings based on
knowledge gained from training data. Finally, we convert images which buildings are detected to polygons, building
outlines are obtained. The data set we use in this paper is located in Ada County of Idaho State, USA. Experiments show
building detection rate with our method is more than 85%. It shows the method adopted in this paper is feasible.