Hi nos, the size of the target surface is... well, it's size.

Every NURBS surface has a 4-sided layout to it the same as your plane there, with a closed surface it's just like you have a sheet of paper that is rolled up so that 2 of its edges are touching one another.

If you can imagine that sheet of paper being rolled up into the shape of your closed target surface there, the size is the size of that sheet.

So also the "seam edge" of the surface (where 2 of the edges of the rolled up surface touch each other) is significant - that will map to 2 of the edges of the flat plane. You may want to use the SrfSeam command in Rhino to move the seam to some other spot if you want your placed surface to start in some other spot than the current seam.


re: keep the size the same - that's generally not possible to do with these kinds of morphing transformations. A surface is not restricted to only have one fixed size in a direction, it can easily have things pinched together in some areas and be wider in other areas, and with your bendy surface it looks like you have that kind of a thing since it isn't just one single rigid shape in one direction of it.

If you wanted to preserve the size, that would require some kind of evenly shaped target and not one that was stretching and deformed in different areas of it.

- Michael