There have been a few recent requests on the 12d Model Forum for ways of fitting a circle/arc through 3 points. Previously, I’ve had the Fit 3pt Arcs (12d App), but that’s designed to fit plan circles to objects. Things like columns, piles, tanks and the like where the surveyor- this was created for surveyors- can only survey points around the outside, but needs a nice clean circular representation for plans. That macro works well for plan circles with varying heights, but these recent requests have been for a true 3d circle.
Mick G posted one of his macros that calculated the centre point and radius for a 3d circle, but didn’t go as far as to actually create the 3d circle element. So, I figured it would be easy enough to create one, based on Mick’s macro. Sure enough, the maths isn’t terribly hard once you’ve brushed up on your vectors and matrices (and vectors and matrices makes this a lot easier). I will mention that there isn’t a 3d circle object type, so this macro actually creates an approximated 3d circle via line segments. There is, however, a field on the panel to let you choose how closely you want to approximate a circle (smaller chord-to-arc tolerance = more points = better approximation).
Anyway, download the macro from the link below and have a play and let me know what you think. The source code is also available on GitLab from the link below. If you find any problems or have any questions, feel free to leave a comment.
Fit 3d Circle GitLab repository- https://gitlab.com/mattmonk/fit_3d_circle_panel