As a consequence of the widespread urban growth there is considerable demand for tools that provide support for planning and monitoring urban conglomerates and their infrastructure. The intensive use of Computer Graphics techniques has made it possible to develop tools capable of operating in low cost platforms with high degree of interactivity and precision.

This dissertation presents SYS_TER - a visual tool for positioning buildings on terrain surfaces. SYS_TER uses appropriate models for the terrain and the objects to be positioned and provides graphical tools for positioning these objects. The current version supports positioning buildings and roads.

Distinct representations are adopted for each type of object. Buildings are solids which are represented, for simplicity, by prisms; roads are seen as thick polygonal lines; terrain surfaces are represented by poliedrical surfaces stored in a topological data structure. An algorithm for combining the different models is provided. Numerical data resulting from this combination - such as the area taken by the buildings and the buried volume of each building - is produced.

As auxiliary tools, we have provided an object editor and a 3-dimensional viewer. The editor allows defining and editing, within the system, the objects to be positioned. The viewer is necessary for better scene exploration.