Welcome! Log In Create A New Profile

Advanced
Re: T-Junctions re-visited
March 20, 2013 11:18AM
Quote
Travis Cobbs
The expectation here is that LDraw files start out with fixed point coordinates, and very often, the transformed coordinate will also be very close to fixed point values (due to transformation matrices often being simple translations, or 90-degree increment rotations). So I wanted to prevent floating point innacuracies from separating two points from each other that were expected to be together.

Ah - I think that the expectation is correct for untransformed locations but likely to be incorrect for transformed ones.

For the untransformed point what you've basically said is: users shouldn't use more than 0.001 LDU, so I'll set up a grid of that spacing, with the gridlines at the half-way points between the canonical values, then bucket. And that makes sense.

But once the transform _stack_ is applied, how do you know where the 'grid lines' in the theoretical 1/1000th LDU grid are? Ignoring scaling, I think that just rotations will hose you. The result of the rotations may be totally misaligned with the grid, and thus two points that were near an even mili-LDU (mLDU?? :-) and would round together now span a 'split point (the points half-way between the canonical values where rounding has to go one way or another).

In other words, I think for untransformed parts your code works but for transformed ones some small sub-set of points that should have been locked together will be pulled apart.

cheers
Ben
SubjectAuthorViewsPosted
T-Junctions re-visited Travis Cobbs543March 11, 2013 10:38PM
Re: T-Junctions re-visited Tim Gould235March 11, 2013 11:31PM
Re: T-Junctions re-visited Roland Melkert203March 12, 2013 11:17AM
Re: T-Junctions re-visited Ben Supnik207March 12, 2013 11:17AM
Re: T-Junctions re-visited Roland Melkert204March 12, 2013 11:22AM
Re: T-Junctions re-visited Ben Supnik197March 12, 2013 11:32AM
Re: T-Junctions re-visited Roland Melkert187March 12, 2013 11:41AM
Re: T-Junctions re-visited Ben Supnik204March 12, 2013 11:55AM
Re: T-Junctions re-visited Roland Melkert197March 13, 2013 10:08AM
Re: T-Junctions re-visited Travis Cobbs232March 13, 2013 11:27AM
Re: T-Junctions re-visited Allen Smith236March 12, 2013 02:01PM
Re: T-Junctions re-visited Michael Heidemann212March 13, 2013 09:27AM
Re: T-Junctions re-visited Ben Supnik206March 13, 2013 10:37AM
Re: T-Junctions re-visited Tim Gould201March 13, 2013 02:31PM
Re: T-Junctions re-visited Michael Heidemann201March 13, 2013 03:42PM
Re: T-Junctions re-visited Michael Heidemann177March 17, 2013 04:35AM
Re: T-Junctions re-visited Ben Supnik173March 17, 2013 08:43AM
Re: T-Junctions re-visited Michael Heidemann178March 17, 2013 08:59AM
Re: T-Junctions re-visited Ben Supnik180March 17, 2013 09:02AM
Re: T-Junctions re-visited Magnus Forsberg181March 17, 2013 09:15AM
Re: T-Junctions re-visited Travis Cobbs199March 17, 2013 10:09PM
Re: T-Junctions re-visited Ben Supnik202March 18, 2013 07:30AM
Re: T-Junctions re-visited Travis Cobbs203March 18, 2013 10:57AM
Re: T-Junctions re-visited Ben Supnik204March 18, 2013 11:27AM
Re: T-Junctions re-visited Travis Cobbs200March 18, 2013 12:23PM
Re: T-Junctions re-visited Ben Supnik215March 18, 2013 01:41PM
Re: T-Junctions re-visited Roland Melkert207March 18, 2013 02:51PM
Re: T-Junctions re-visited Travis Cobbs196March 18, 2013 02:59PM
Re: T-Junctions re-visited Roland Melkert193March 18, 2013 03:41PM
Re: T-Junctions re-visited Ben Supnik208March 18, 2013 06:09PM
Re: T-Junctions re-visited Roland Melkert204March 19, 2013 11:38AM
Re: T-Junctions re-visited Ben Supnik214March 19, 2013 11:43AM
Re: T-Junctions re-visited Roland Melkert226March 19, 2013 07:07PM
Re: T-Junctions re-visited Travis Cobbs204March 19, 2013 10:13PM
Re: T-Junctions re-visited Tim Gould208March 20, 2013 03:56AM
Re: T-Junctions re-visited Travis Cobbs200March 20, 2013 10:13AM
Re: T-Junctions re-visited Ben Supnik184March 20, 2013 10:23AM
Re: T-Junctions re-visited Travis Cobbs199March 20, 2013 10:29AM
Re: T-Junctions re-visited Travis Cobbs193March 20, 2013 10:26AM
Re: T-Junctions re-visited Ben Supnik172March 20, 2013 11:18AM
Re: T-Junctions re-visited Ben Supnik190March 20, 2013 06:42AM
Re: T-Junctions re-visited Roland Melkert195March 20, 2013 11:36AM
Re: T-Junctions re-visited Philippe Hurbain191March 20, 2013 06:36AM
Re: T-Junctions re-visited Ben Supnik201March 20, 2013 06:58AM
Re: T-Junctions re-visited Allen Smith189March 20, 2013 09:08AM
Re: T-Junctions re-visited Roland Melkert209March 20, 2013 11:35AM
Re: T-Junctions re-visited Ben Supnik524March 20, 2013 11:50AM
Re: T-Junctions re-visited Michael Heidemann211March 18, 2013 03:54PM
Re: T-Junctions re-visited Roland Melkert203March 13, 2013 10:03AM
Re: T-Junctions re-visited Tim Gould191March 13, 2013 03:56PM
Re: T-Junctions re-visited Sergio Reano183March 13, 2013 03:51PM
Re: T-Junctions re-visited Roland Melkert237March 13, 2013 04:36PM
Re: T-Junctions re-visited Tim Gould198March 13, 2013 05:10PM
Re: T-Junctions re-visited Ben Supnik187March 14, 2013 08:17PM
Re: T-Junctions re-visited Tim Gould255March 14, 2013 08:41PM
Re: T-Junctions re-visited Ben Supnik232March 15, 2013 10:56AM
Re: T-Junctions re-visited Roland Melkert203March 15, 2013 11:36AM
Re: T-Junctions re-visited Ben Supnik192March 13, 2013 06:58PM
Re: T-Junctions re-visited Roland Melkert184March 13, 2013 07:27PM
Re: T-Junctions re-visited Ben Supnik174March 13, 2013 07:37PM
Re: T-Junctions re-visited Roland Melkert186March 13, 2013 07:59PM
Re: T-Junctions re-visited Ben Supnik210March 13, 2013 08:18PM
Re: T-Junctions re-visited Travis Cobbs226March 14, 2013 03:23PM
Re: T-Junctions re-visited Roland Melkert230March 14, 2013 03:34PM
Re: T-Junctions re-visited Tim Gould236March 14, 2013 03:41PM
Re: T-Junctions re-visited Roland Melkert209March 15, 2013 11:33AM
Re: T-Junctions re-visited Tim Gould173March 13, 2013 07:43PM
Re: T-Junctions re-visited Roland Melkert187March 13, 2013 08:08PM
Re: T-Junctions re-visited Tim Gould189March 13, 2013 08:18PM
Re: T-Junctions re-visited Ben Supnik234March 14, 2013 08:15PM
Re: T-Junctions re-visited Roland Melkert235March 15, 2013 11:29AM
Re: T-Junctions re-visited Travis Cobbs201March 15, 2013 12:27PM
Re: T-Junctions re-visited Ben Supnik208March 15, 2013 05:08PM
Re: T-Junctions re-visited Travis Cobbs201March 16, 2013 11:29PM
Re: T-Junctions re-visited Ben Supnik175March 17, 2013 08:58AM
Re: T-Junctions re-visited Roland Melkert177March 17, 2013 12:35PM
Re: T-Junctions re-visited Travis Cobbs196March 18, 2013 12:28PM
Re: T-Junctions re-visited Travis Cobbs209March 18, 2013 12:32PM
Re: T-Junctions re-visited Roland Melkert198March 18, 2013 05:00PM
Re: T-Junctions re-visited Travis Cobbs230March 18, 2013 11:05PM
Re: T-Junctions re-visited Roland Melkert240March 19, 2013 11:38AM
Re: T-Junctions re-visited Sergio Reano226March 26, 2013 02:46PM
Re: T-Junctions re-visited Roland Melkert191March 27, 2013 11:19AM
Re: T-Junctions re-visited Sergio Reano232March 27, 2013 01:48PM



Sorry, only registered users may post in this forum.

Click here to login