BRL-CAD tutorial series

Original publisher: Aberdeen Proving Ground, MD : Army Research Laboratory, [2001- OCLC Number: (OCoLC)58393464 Subject: Armored vehicles, Military -- Models -- Computer simulation. Excerpt: ... Rendered image of an extrusion die. CSG approach in which a cone is BREP approach in which four subtracted from a cylinder. surfaces are stitched together. Figure 1. CSG and BREP approaches to representing an extrusion die ( Tanenbaum, 2001 ). For BRL-CAD, a simple type of BREP is available in the form of triangles; it is called the Bag of Triangles ( BOT ) primitive. If the BREP object consists of all triangles, the BRL-CAD representation can be an exact duplicate. But more often, a BREP object consists of smooth, curved surfaces, meaning the BRL-CAD triangle representation will be an approximation of the object. Note that this approximation may be made as close to the true surface as desired, but at the cost of more, smaller triangles ( see figure 2 ) ( Tanenbaum, 2001 ). Thus, the higher degree of smoothness means the greater the impact on file size and performance of any application trying to employ all the triangles. Because most commercial CAD systems have the capability to produce tessellated approximations of their BREP objects, some converters to BRL-CAD ( e.g., those with Pro / E and Unigraphics ) take advantage of these capabilities. In addition, the previously mentioned STL format, which represents solid objects entirely with triangles, offers the community a universal ( albeit crude ) way to convert BRL-CAD geometry ( via the g-stl converter ) to nearly any commercial CAD system. 5