Hi MO, the uv can be any object that has .x and .y properties on it. You can use a 3D point for it where you've just stored the x and y values, the z value will just be ignored.

The actual x and y (usually referred to as u and v when being used in parameter space) values you use should be in the uv rectangle for the surface's parameter range.

The lower left corner of the surface's parameter range is on a .domainMin property on the face, and the upper right corner of the surface's parameter range is on a .domainMax property on the face. Each of those face.domainMin and face.domainMax properties will give back a 2d point object with x and y values.

If you want something in the center of the parameter range you could do x = (face.domainMin.x + face.domainMax.x)/2 and y = (face.domainMin.y + face.domainMax.y)/2 .

- Michael