Edge Lines

 The algorithms for the Srf-Node Method, the Mesh Method, and the Tessellated-Mesh Method were all integrated into the Alpha_1 system, using the existing NURBS surface evaluators and functions when possible. Alpha_1 is a B-spline research system which integrates computer graphics, modeling (geometric, simulation, and physically based), rendering (realistic and non-realistic), virtual prototyping, mechanical design, visualization, animation, teleconferencing, and human-computer interaction. In the viewer called ``motif3d,'' one can load a NURBS model and toggle display options such as isolines, the control mesh, and Phong shading. I added the option to display silhouettes as well as the new shading, as explained in the next section.

Using the JOT program, a Utah-Brown collaboration, I was able to use the OpenGL shading model approximation presented in the next section along with the silhouette finding technique of Markosian et al. to produce interactive illustrations for polygonal models, as shown in Figure 5.1. The original Sketch [42] system was deeply intertwined with the Brown UGA  [41] system, which prevented easy distribution of Sketch. To overcome this problem, Sketch was rewritten as part of the JOT framework. JOT allows Sketch to work with different underlying graphics kernels that provide basic services such as CSGs, intersection, creation of geometric primitives, etc. Currently JOT works with various graphics kernels including Alpha_1, the Amodeler package from Autodesk, ARCADE (from Fraunhofer IGD), and a partial implementation on top of Open Inventor. In addition, JOT can be used on various different UNIX platforms and Windows NT.

  

Image of with edge lines only.	Image with new shading and edge lines.
Figure 5.1: An Alpha_1 model that was tessellated and imported into the JOT NPR Program.