Hi Peer, the problem you're running into here is that the curves that look like a circle and arc are not precise circle or arc analytic curves, they are general spline curves that closely resemble a circle and arc but not quite to the (rather tight) precision level that MoI currently uses to detect if a curve is the shape of a circle or arc.

To solve this currently I think you would need to replace D with a 3 point circle and R with a 3 point arc.

You can do this by selecting the circle, then run Draw curve > Circles > 3 pts, place 3 roughly equidistant points and then hit delete to remove the original curve. Same thing with the arc except using the 3 pts Arc tool.

I guess there are a couple of possible ways to improve this so you wouldn't need to do that. One possibility would be to loosen the tolerance used to detect if any curve is a line, circle or arc.

Another possibility could be to allow a radius dimension to be put on any curve with the value using the curvature at the picked point. Rhino does this but it seems kind of dangerous.

Or another could be to do some shape analysis on the result of the projected curves in the 2D drawing generation and replace with exact circles and arcs at this spot. This seems like it may be the best way because the other methods could lead to a false sense of accuracy.

- Michael