CGAL users discussion list

[paulo <>]

Hi,

after debugging CGAL's code, there's something I don't understand, and 
looks like a bug.

In the square border parameterizer it computes the offsets 0, 1, 2 and 3 
using the border iterator, which iterates through the vertices 
apparently in a clockwise way, which in my case yields the sequence 
((-1, -1, 0) , (-1,  1, 0) , ( 1,  1, 0) ,( 1, -1, 0)).
But afterwards it parameterizes the mesh in a counterclockwise way (?!) 
which yields ((-1, -1, 0), ( 1, -1, 0), ( 1,  1, 0), (-1,  1, 0)).
This does not make sense to me.

But if it is a bug how come no one found it before? No one uses this code?

Can any one related to this implementation say something please?
I feal tempted to change the code, but I would like to hear what other 
people have to say.

Thank you.
Paulo


paulo wrote:
> Hi Laurent,
>
> thank you so much for your help.
> I could only test it today, and it helped allot.
>
> I'm still debugging, but I'm getting a strange (in my opinion) result.
> I'm inputing (in this sequence):
> vertices:
> (-1, -1, 0)
> ( 1, -1, 0)
> ( 1,  1, 0)
> (-1,  1, 0)
> Faces:
> (0,1,2)
> (0,2,3)
>
> I get a parameterization:
> (0,0)
> (0,1) !?
> (1,1)
> (1,0) !?
>
> This flips two of the vertices.
>
> Shouldn't it be:
> (0,0)
> (1,0)
> (1,1)
> (0,1)
>
> Am I understanding something wrong?
>
> Thank you.
>
> Best regards,
> Paulo