Is useful in topography for "Digital Terrain Modeling" (DTM) by "Triangulated Irregular Network" (TIN), representation (by 3DPOLY, SPLINE or BLOCK entities) and editing (modify, delete or add) of 3D points, and for triangulation, isolines, color-filled contour map, cross sections, longitudinal profile, 2D entities (Line or PLine) projection over a DTM, conversion of a TIN to a regular grid of points and for conversion of existing isolines resulting from maps in points and then in TIN. It exists a modifiable library for codes and BLOCKs. The coordinates, the code and the position (in 3DPOLY or SPLINE) of the points can be modified interactively. You can represent the geological stratification resulting from drilling. You can calculate the volume, 3D area and center of gravity of some bodies limited by 3DFACE entities. DXF files can be loaded or saved. RCAD graphic core, distributed together with RTOPO, provides OpenGL real-time orbit, pan, zoom, shading and lighting.