On Wed, Oct 15, 2014 at 7:09 AM, Christopher Sean Morrison <brl...@mac.com> wrote: > > After validation and comparisons were completed (several years ago) the > options remained because there is a limitation. Sometimes TIE prep is *much* > slower than our traditional method. So slow that "old_prep+old_shot < > tie_pre+tie_shot” … It turns out that tie_shot is very much superior to > old_shot for most geometry, but tie_prep is nearly always even more slow than > old_prep and that differential often dominates. > > The downside is that it’s more work and we may have to follow our deprecation > policy to change user-visible options if they were documented somewhere.
Nevertheless, it looks like a better solution, so I will read the CHANGES file and implement it in the next days. > Those applications are really just using the rt_bot_prep() interface and — in > that function — a heuristic is calculated to estimate which one is better to > use, TIE or traditional. An initial heuristic could be as simple as if > #triangles >= MIN_TRIANGLES_FOR_TIE, run bottie_prep_double(), else > rt_bot_prep_*(). A more involved one might entail creating a single > triangle, running prep and running shot for TIE and traditional, and > calculating an estimate for when one outperforms the other. Lots of > possibilities. I made a little research to find the best value for MIN_TRIANGLES_FOR_TIE[1]. I made a C++ program that generates a BoT with a specified number of triangles, whose vertices are organized like the nodes of the latitude-longitude grid of a sphere. The output is in the form of a Tcl script which is then converted to a .g database using asc2g. I ran rt for a huge number of files generated in this way both with LIBRT_BOT_MINTIE unset and set to 1 and I logged the execution times. Then I plotted the results in Octave and I got these functions[2], which are a bit curious as I expected some polynomial-like graphs which I could have approximated to find their intersection. Anyway, it comes out that the best value is around 32 triangles. > More clear? Clear as mud? It is more clear now. Thank you. Cheers! Stefan [1] https://drive.google.com/file/d/0BzUvtJl1x3QBdnhpWXFueV9Qajg/view?usp=sharing [2] http://s1.postimg.org/wsclre4rz/imag.png ------------------------------------------------------------------------------ Comprehensive Server Monitoring with Site24x7. Monitor 10 servers for $9/Month. Get alerted through email, SMS, voice calls or mobile push notifications. Take corrective actions from your mobile device. http://p.sf.net/sfu/Zoho _______________________________________________ BRL-CAD Developer mailing list brlcad-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-devel
