(u,v) parameters & PointOnFace

[J.Pelfrene]

Hi all,

I was wondering about the Face.PointOnFace and Evaluator.GetPointAtParam methods.

What are the conventions for the parameters in the (u,v)-space for faces? And linear parametric space for edges?
For instance is parameter (0,0) always somewhere at the centre of a face, or at a vertex? How can the (u,v) parameters be used to find a specific location on the face?

And with the PointOnFace method, does it return a random point on the face? If so, is it also a different point every time the method is called?

Thanks,

Joren

[WCrihfield]

Hi @J.Pelfrene.  Those are pretty good questions.  And most likely only the only ones that can properly answer them are the ones at Autodesk who designed those Inventor API methods.  In general the term parameter or parameters being used within the 'Evaluator' tools are representing a percentage (a Double between 0.0 and 1.0) that represents a location at that percentage of the way across the geometry.  With a line, there is often a start point and an end point, but with a face, since they can be nearly any shape, it is not that simple.  The online help page for the Face.PointOnFace property obviously doesn't offer much detail about where that point may be, other than "somewhere on the interior of the face".  That leads us to believe that it will not be on a vertex or edge of the Face, but we can't even be sure about that.  The online help page for the Face.Evaluator.GetPointAtParam method likewise doesn't offer much information about what the "u-v" parameters represent or where they may be based from.  You may need to contact someone at Autodesk with this inquiry.