On Jul 1, 2014, at 12:53 AM, Gurwinder Singh Bains wrote: > In "BRL-CAD documentation Volume IV – Converting Geometry Between > BRL-CAD and Other Formats" different formats are given in which we can > convert BRL-CAD model i.e. .g format to another .xyz format. I convert > my .g file model into STL, VRML formats. Conversion with the given > command in this documentation is completed successfully but on > comparing my converted model with my original BRL-CAD model it looks > less accurate.
Since formats like STL and VRML are polygonal formats, your model is converted from a set of smooth (mathematically perfect) into polygons. This conversion (called tessellation) is necessarily an approximation and controlled by a number of tolerance values. Note the converter usage statement if you run g-stl without any arguments: Usage: g-stl [-bviM8] [-xX lvl] [-a abs_tess_tol] [-r rel_tess_tol] [-n norm_tess_tol] [-D dist_calc_tol] [-o output_file_name.stl | -m directory_name] brlcad_db.g object(s) The tolerance parameters are -a, -r, -n, and -D. These tolerance settings control the "accuracy" and fidelity of the polygonal approximation but require some exploration to find suitable values. What makes for a good value entirely depends on how many polygons you want to result, the overall size of your model, and other factors. The two that will probably be most useful to you are the normal and absolute tolerance values... For example, setting g-stl -n 1.0 should create a polygon for every 1-degree difference in curvature. Since your model has a lot of circular edges, this should me a considerable visual improvement. Setting the absolute tolerance to some sub-zero value should have a similar effect, but be careful to not specify a number too small or you may inadvertently create many GB of polygons (or worse). When converting to any polygonal format, you want to specify the tolerance values specific to your model. Do that, and you'll get something that looks much better. Cheers! Sean ------------------------------------------------------------------------------ Open source business process management suite built on Java and Eclipse Turn processes into business applications with Bonita BPM Community Edition Quickly connect people, data, and systems into organized workflows Winner of BOSSIE, CODIE, OW2 and Gartner awards http://p.sf.net/sfu/Bonitasoft _______________________________________________ BRL-CAD Developer mailing list brlcad-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-devel
