Surface Blending - Unexpected pinching

 From:  Michael Gibson
1546.8 In reply to 1546.6 
Hi Steve,

> I just looked at creating the blend in Rhino4, the results will
> help to show what I mean:-

Yup, that is actually the same problem, if you look at the ends of each of those isoparms, it is a slanted type arrangement.

Basically, you can kind of imagine that blending first creates a set of lines that are connected between the 2 edges.

That line is then converted into a smooth curve segment, and the length of the line determines a kind of "bulge factor" for the shape.

When the line is slanted, it has a bigger length than a non-slanted one, and that bigger length causes too much bulging of the smooth part.

The key to preventing this is getting better matching points between the curves.

- Michael