On Tue, Jun 28, 2016 at 11:19 PM, Bojian Wu <ustcb...@gmail.com> wrote: > Hi everyone, > > Because I have already drafted a rough implementation of plate mode > NURBS ray tracing, and it works well for me now, I also put all the tests on > my blog, please check it, if you have any issues, please let me know and I > will make proper refinement, it will be much grateful. :-)
So the first test of accuracy to make on a plate mode nurbs raytrace is to take the portion of the sphere that you are raytracing plate mode, calculate mathematically what the volume should be for a "slice" of a spherical shell with your assigned thickness, and use a tool such as gqa to verify that the volume defined by the solid according to raytracing is a close match for the the mathematically expected volume. > So, recently, I want to shift my attention to the tessellation of NURBS, > it is much more challenging. Because after my research, I find that there > are several related methods that can be used for the purpose. There also > exists an old implementation in BRL-CAD(nurb_tess.c), it is a kind of > mapping from triangulation of 2D parameter space to 3D surface space within > given approximation errors bound(I have summerized this method on my > blog.:-) ), it is a simple and effective method. Before you do, make sure you and your mentor agree that the plate mode NURBS work is actually done. That said, there is indeed quite a lot of useful work that can be done with our tessellation routines. There is actually quite a bit more work that has been done with NURBS tessellation - our "modern" tessellation code for NURBS uses the poly2tri code for generating triangles (see src/other/poly2tri and the places in librt where that library is used.) The most significant lack for our current poly2tri tessellation is the inability to generate "watertight" tessellations - each surface is separately tessellated, but those tessellations are not properly joined at the edges to form closed solids. We would also like to explore the work done by the bitfighter devs to use clipper's logic as a "clean-up" pre-processing step before generating triangles with poly2tri: https://github.com/raptor/clip2tri - this has the possibility to increase the robustness of our tessellations. A "warm-up" to those more difficult tasks might be to translate the poly2tri logic from its current src/other code into our data structures and data types in libbg. Cheers, CY ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ BRL-CAD Developer mailing list brlcad-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-devel
