On Tue, 11 Mar 2003 08:36:24 +0200, Pasi Paasiala <[EMAIL PROTECTED]> wrote:
>Thanks for taking the bug seriously. I also drew the case again in XZ plane
>and by twisting my right hand seriously I found out that actually the outer
>bound is CW and inner bound is CCW,
You are right, so if you change the outer loop order to CCW, like this one:
new Point3d(2., 0.0, 0.0),
new Point3d(0.0, 0.0, 0.0),
new Point3d(0.0, 0.0, 1.3),
new Point3d(2., 0.0, 1.3),
The triangulation works correctly.
The paper for FIST says it will orient outer loop to CCW, inner loop to CW, but if you
really order the inner bound as CW like the following one:
new Point3d(1.93, 0.0, 0.07),
new Point3d(1.93, 0.0, 1.13),
new Point3d(0.07, 0.0, 1.13),
new Point3d(0.07, 0.0, 0.07),
the triangulation fails again. I don't know why?
------white
>-----Original Message-----
>From: Discussion list for Java 3D API
>[mailto:[EMAIL PROTECTED] Behalf Of Mark Hood
>Sent: 11. maaliskuuta 2003 6:40
>To: [EMAIL PROTECTED]
>Subject: Re: [JAVA3D] Please have a look at the triangulation problem
>
>
>> Date: Mon, 10 Mar 2003 09:17:09 +0200
>> From: Pasi Paasiala <[EMAIL PROTECTED]>
>>
>> Could you finally have a look in the triangulation problem that we are
>> constantly having? There is a simple test case that you can use to verify
>> (and possibly fix) the problem.
>>
>> The problem is that the following data should create a rectangle with a
>hole
>> inside:
>>
>> Point3d[] coordinates = {
>> //outer bounds of the polygon
>> new Point3d(2., 0.0, 0.0),
>> new Point3d(2., 0.0, 1.3),
>> new Point3d(0.0, 0.0, 1.3),
>> new Point3d(0.0, 0.0, 0.0),
>>
>> //the hole
>> new Point3d(1.93, 0.0, 0.07),
>> new Point3d(0.07, 0.0, 0.07),
>> new Point3d(0.07, 0.0, 1.13),
>> new Point3d(1.93, 0.0, 1.13)
>> };
>>
>
>OK, found the problem here.
>
>The FIST algorithm works by first projecting the polygon onto a plane
>and then working from the 2D projected points. It does this by
>computing an "average" normal from every 3 points along each contour.
>
>This works fine for polygons without holes. It also works fine for
>polygons with holes as long as the vertex windings are the same for the
>holes and the outer boundary. But in the above case, the normals for
>the outer boundary and whole are flipped because of the opposite
>windings, so the "average" normal is zero-length [0 0 0].
>
>Instead of throwing an exception, the triangulator substitutes [0 0 1]
>for the normal. This causes all the projected points to have a Y
>coordinate of 0 in the above case, so the triangulation fails.
>
>Workarounds: the algorithm always works if the original points are in
>the XY plane. It also always works if the outer boundary and the holes
>have the same winding order. It would also work even in the XZ and YZ
>planes with inconsistent winding if the number of contours is odd.
>
>The code looks like it's supposed to handle all cases -- it tries to
>reverse the windings to a canonical form, with the outer boundary
>ordered CCW and the inner holes ordered CW. So I think this is a
>probably a legitimate bug, but I need to find out what the real
>capabilities of the code are before determining its status and
>evaluating whether we can supply a fix.
>
>-- Mark Hood
>
> ==========================================================================
>To unsubscribe, send email to [EMAIL PROTECTED] and include in the body
>of the message "signoff JAVA3D-INTEREST". For general help, send email to
>[EMAIL PROTECTED] and include in the body of the message "help".
>
===========================================================================
To unsubscribe, send email to [EMAIL PROTECTED] and include in the body
of the message "signoff JAVA3D-INTEREST". For general help, send email to
[EMAIL PROTECTED] and include in the body of the message "help".
