I have three arcs with different radii. When I loft them together I get a Polysurface instead of a Surface.
When I extract the control points of the arcs, one has 5 and the other has 3. I believe this is the problem, but is there a way to tell Grasshopper how many control points the arc should have?
I would like to solve this problem without rebuilding the curves, if possible.
Try fitCrv then loft, or use loft set to refit option.
Always the same time 
Thanks for the suggestions, but is there a way to do it without changing the curves? I don’t want to rebuild or refit the surfaces or the curves, because it is important to the geometry that the arcs are parts of perfect circles.
Fitting will only change the curve to a very very small tolerance. It is the fit Curves ft input. use degree 3 for the D input.
Perhaps you could just help me understand why lofting two arcs sometimes generates a polysurface? Or why some arcs are drawn with 5 control points instead of 3?
Arcs are degree 2 curves, the shape is usually made with low control point count but with varied weights on the points. Control points interpolate well for lofting. Weights do not interpolate well especially if each curve has different weights, so you get instead polysurface or ruled surface. That’s why I suggest to fit to degree 3. You will have more control points but better interpolation. As for why 3 points vs 5, because sometimes the shape you are making requires 3 points to make it, others it requires 5, depends on the shape.
