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Subject:	Re: Hidden surface removal, and vertex order in part/primitive DAT files
Newsgroups:	lugnet.cad.dev
Date:	Sat, 2 Oct 1999 19:46:03 GMT
Viewed:	687 times

Gary Williams wrote: > > Jean-Pierre PARIS wrote in message <37F3B871.74AE196F@wanadoo.fr>... > [snip] > > My algorithm doesn't require the vertices to exactly match; I was intending > to pass one ray per polygon through the dat object, not an arbitrarily large > number. And only if a ray penetrated an even number of polygons would those > polygons be automatically processed. Sorry, but I think that the even/odd algorithm only work on 'correct' solids. For example, if you take a 'bad' box made of 6 faces that have holes beween them, your algorithm can lit an inside face. And in some parts, such a situation exists. Thus my first too that tries to suppres these holes, which came after rounding coordinates numbers > [snip] > That's a clever algorithm. Thanks! But I would be really happy if my code could be used to start the orientation process for all Ldraw bricks! > Assuming (after all close vertices are matched up) that no polygons have > zero neighbors, after determining the orientation of one polygon, you could > visit each neighboring polygon (somewhat like a flood fill algorithm) and > determine its orientation easily. Only one ray would be needed in the > entire process. I have coded this flood fill algo. The main problem has be mentioned above: for some reason, all parts are not made with matching edges. For example, the studs primitive simply sits on the box5. In other parts, one can encouter rounding pbs... So you have to launch more than one ray OR to build a real solid. Another tool I coded tried to do this buiding but it has not been really successful... > -Gary bye jp

Message has 2 Replies:

		Re: Hidden surface removal, and vertex order in part/primitive DAT files
(...) This isn't automatic, but what if the program interrogates the user to pick a side which is facing outward? From that information, the program could then mark-up all adjacent sides. If the program ran out of sides, it could re-interrogate for (...) (25 years ago, 3-Oct-99, to lugnet.cad.dev)

		Re: Hidden surface removal, and vertex order in part/primitive DAT files
Jean-Pierre PARIS wrote in message <37F660FB.1EC77AC9@w...doo.fr>... (...) I see where you're coming from now. You're right. (...) could (...) It's starting to sound like user intervention would be needed in most, if not all, cases. Maybe it would (...) (25 years ago, 3-Oct-99, to lugnet.cad.dev)

Message is in Reply To:

		Re: Hidden surface removal, and vertex order in part/primitive DAT files
Jean-Pierre PARIS wrote in message <37F3B871.74AE196F@w...doo.fr>... (...) My algorithm doesn't require the vertices to exactly match; I was intending to pass one ray per polygon through the dat object, not an arbitrarily large number. And only if (...) (25 years ago, 30-Sep-99, to lugnet.cad.dev)

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