drb@eecg.toronto.edu (David R. Blythe) (06/17/91)
I have been working on modifications to the NCSA isosurface visualizer to make it run faster and do more things on the SGI workstation over the past year to the point where it has become a useful part of our visualization & movie making arsenal at OCLSC. For anyone interested, the source code is available for anonymous ftp on bessel.clsc.utoronto.ca in the file pub/clsc/isovis.tar.Z Keep in mind that this is a tool with a very specific purpose, to generate isosurfaces from a regular 3D volume of scalar data. It can save the polygons in a file for fancier rendering using programs from Wavefront, etc. Or you can manipulate the surface interactively on an SGI workstation to get a better feel for its structure. The distribution is a bit short on example data sets (you can get them from NCSA) but there is one small dataset available in pub/clsc/elec.40x40x40.Z which you can test the program with, e.g. isovis -raw 40 40 40 -p -norm 2 -mc 0. 1. 1. elec.40x40x40 .01 have fun, david blythe A copy of the README file follows: ----------------------------------------------------------------------------- this is a heavily modified version of NCSA isovis which runs faster, generates smoother surfaces and supports some interactivity on the SGI platform. The basic isovis program extracts a constant-valued (iso) surface from a regular 3D volume of scalar data using Lorenson & Cline's marching cubes algorithm. The major speed improvements I made were to utilize coherency to reduce the number of redundant computations. Additionally the code has been restructured so it vectorizes on a CRAY (although it only gets about 15Mflops on an X/MP). A second major addition to the program is the ability to compute normals at each triangle vertex by computing an approximation to the gradient at each cube corner using a central difference. This results in far superior shading (i.e. considerably less faceting) at greater computational expense. The interactive features are somewhat primitive, but on a suitably endowed SGI machine (double buffered RGB, zbuffer) you can rotate and translate the isosurface. Isovis goes to great lengths to transform the original tesselation into long triangle and line strips for improved drawing performance on the SGI platform. I have regularly used it to display upto 50K triangles on a 4D/70GT with 16M of memory and upto 200K triangles with a 210GTX with 64M of memory. [In general memory is the limiting factor] It is missing many features, but with the arrival of APE and other programs I probably won't be adding too much more to this program. However, if you have an SGI workstation and regular 3D gridded data and want to see isosurfaces *fast* this is the program for you :-) david blythe formerly ontario centre for large scale computation drb@clsc.utoronto.ca direct coments and suggestions to blythe@sgi.com