question about convexity

Does the convexity argument need to be exact (i.e. exact maximum number
of
front/back faces a ray might intersect) or just large enough?  I've
attached
a file that I can't get to display right in preview mode (it comes out
sort
of inside-out), that looks fine when rendered.  I'm guess I have the
wrong
convexity argument or have supplied it in the wrong place.

The file it kind of long but it is mostly just a profile that gets
substituted
in for a rotational extrusion, in form it is like this:

difference (convexity = 1) {
  rotate_extrude (convexity = 10, $fn = 30)
    polygon (@@openscad_poly@@);
  translate ([0, 0, 0.430])
      rotate (0 * 360.0 / 6, [0, 0, 1])
        translate ([0, 2.85, 0])
          cylinder (h = 0.476, r = 0.338 / 2.0, $fn = 10);
}

It also works fine if 'difference' is replaced with 'union'.

Britton

try it like this. convexity must be just large enough.

 polygon (@@openscad_poly@@, convexity=10);

On Wed, 27 Jan 2010 04:26 +0100, "Philipp Tiefenbacher"
<[hidden email]> wrote:
> try it like this. convexity must be just large enough.
>
>  polygon (@@openscad_poly@@, convexity=10);

No luck.  Even with convexity=10 arguments for every function
(including the for loop, where it seems to do no harm), the same inside-
out effect occurs.

Britton