[help-3dldf] Re: [metapost] Re: [metafont] Re: Intersections of NURBs

Laurence Finston lfinsto1 at gwdg.de
Mon Jan 31 11:15:50 CET 2005

On Sun, 30 Jan 2005, L. Nobre G. wrote:

> I think the following "visualization" agrees with both Laurence and Larry
> views:

> Accordingly to Laurence you don't see the control points B and C
> (they are on the southern hemisphere, z-coordinates are less than or
> equal to that of `Focus.position') but you should see the bezier curve on
> your left. If control points B and C were projected as Larry explained they
> would show up on your right. Right?

Thanks.  I'll have to leave it to Larry (or someone else)
to answer, since I don't know.

In case anyone's wondering, the reason why points with the same
z-coordinate as Focus::position can't be projected is because this
would involve division by 0.  Objects consisting of points whose
z-coordinates are greater than 0 could be projected, but are generally
culled, because people don't see that way.

Incidentally, I'd be quite interested to know how you do surface hiding in
FEATPOST, if you'd care to explain.


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