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Subject: 
Re: Collinear vertices warning on very small triangels
Newsgroups: 
lugnet.cad.dat.parts
Date: 
Tue, 1 Mar 2005 01:18:44 GMT
Viewed: 
3433 times
  
In lugnet.cad.dat.parts, Willy Tschager wrote:
In lugnet.cad.dat.parts, Ross Crawford wrote:
In lugnet.cad.dat.parts, Willy Tschager wrote:
hi lars,

I get L3P collinear vertices warning on these very small triangels:

Hi Willy, there was a thread about that recently, coincidentally someone else
named Will :) http://news.lugnet.com/cad/dev/?n=10023

hi rosco,

thx for pointing. interesting thread. even after so many years I still find out
something new (that's why I love LDraw :-) L3Lab and L3p share code ... hmmm ...

Yes, reading and parsing files is common code. You can read more here:
http://www.hassings.dk/l3/l3lab.html

The next version of L3P/L3Lab do accept your small triangles, see
http://news.lugnet.com/cad/dev/?n=10033

If you set the warning level to 2 (-w2) you will see L3P's warnings
(which should have been errors, since they are skipped...)

L3Lab does not draw concave quads like this:

4 4 0.603 19.885 1.569 0.902 19.803 1.569 0.294 19.935 1.569 1.348 23.306 1.569
4 4 1.962 19.146 1.569 2.19 18.899 1.569 1.718 19.357 1.569 4.658 22.467 1.569
4 4 3.365 15.157 1.569 3.413 14.491 1.569 3.302 15.76 1.569 8.689 15.058 1.569
4 4 3.46 10.85 1.569 8.857 11.827 1.569 8.844 11.056 1.569 8.806 10.292 1.569

I just copied the four quads into a file and opened it in L3Lab
and they showed up nicely. You may set the zoom to 4000.

but you won't get any warning when checking with L3P. you will have to use
LDView to find out what's wrong:

Concave quad split into two triangles.
File: C:\...\Concave.dat
Line #7
Line: 4 4 0.603 19.885 1.569 0.902 19.803 1.569 0.294 19.935 1.569 1.348 23.306 1.569
Original Quad: <0.603 19.9 1.57> <0.902 19.8 1.57> <0.294 19.9 1.57> <1.35 23.3
1.57>
Triangle 1: <0.603 19.9 1.57> <0.902 19.8 1.57> <1.35 23.3 1.57>
Triangle 2: <0.902 19.8 1.57> <0.294 19.9 1.57> <1.35 23.3 1.57>

lars, will "concave-checking" be part of the new L3P version?

But there's nothing wrong!
Most (if not all) programs only deal with triangles and thus split a quad into two triangles.
You can split a convex quad in two ways, but there's only one way to split a concave quad.
L3Lab (and L3P) correctly detects the concave quad and splits the quad the right way.
/Lars



Message has 1 Reply:
  Re: Collinear vertices warning on very small triangels
 
(...) I based the error check code in LDDP on the L3P -check code you published a while ago. Since you have significantly updated this code are you planning on doing sharing again? If you you don't want to release this publically, would you consider (...) (20 years ago, 1-Mar-05, to lugnet.cad.dat.parts)

Message is in Reply To:
  Re: Collinear vertices warning on very small triangels  [DAT]
 
(...) thx for pointing. interesting thread. even after so many years I still find out something new (that's why I love LDraw :-) L3Lab and L3p share code ... hmmm ... L3Lab does not draw concave quads like this: 4 4 0.603 19.885 1.569 0.902 19.803 (...) (20 years ago, 27-Feb-05, to lugnet.cad.dat.parts)

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