[gts-general] Cutting a model up...

[Paul <pau...@st...>]

I want my program to be able to cut up a model using a very simple method
- by removing all triangles containing a point on one side of a plane.

I initially tried calling:

	gts_surface_foreach_face(s, (GtsFunc) cut_model, NULL);

with the function cut_model being:

	static void cut_model( GtsTriangle *t, NULL )
	{
		GtsPoint * p1, * p2, * p3;
	 
		gts_triangle_vertices (t,
					(GtsVertex **) &p1,
					(GtsVertex **) &p2,
					(GtsVertex **) &p3);
		if (p1->y < 0 || p2->y < 0 || p3->y < 0) {
			gts_object_destroy(GTS_OBJECT(t));		
		}
	}

I didn't know whether I should be receiving a GtsTriangle or a GtsFace, so
I tried both but the program fails on the assert - keep_faces ==
FALSE.  This is set in the GTS function gts_surface_foreach_face.  I have
also tried passing an array to store all the triangles in that I want to
delete and then deleteing them afterwards but this doesn't seem to work
either.

So any pointers as to what I should be doing would be very helpful, but
here are a few questions...

(1) can I just delete a GtsTriangle, and
(2) does it update the information associated with the surrounding
triangles?
(3) can I just delete a GtsFace, and
(4) does it update the information associated with the surrounding
triangles?
(5) which should I use - and what is the difference?
(6) is there something better to use than gts_surface_foreach_face to get
the information I need.

BTW I don't want to use boolean operations (not sure I can)  because I
don't want the structure changed.

Thanks,

Paul