Hi Sean - the best way I know of to get the arcs is to use
Arc > 3Point snapping to the polyline vertices, but there is no ‘convert’.
Circle > FitPoints can also help, but you need to turn on control points on the polyline and select the ones you want.
@seanprokopec - in case it helps, I had a few Python scripts that attempt to reverse engineer arcs from points and polylines - I bundled them into a plugin fo convenience, you may be able to save a bit of time. If you download and unblock:
the plug-in and then drag it onto Rhino, you’ll get these commands:
Arc3Pt -the same as the Rhino command Arc > Start, End, PointOnArc only it reads out the radius and copies the radius to the clipboard - this is handy for checking the radius on an arc like polyline and then adding a fillet between two lines that has that same radius - this way the arc is sure to be tangent to the lines.
Arc3PointFromPoints - you give the tool points or control points (e.g. selected control points in an arc-like area of a polyline) and it makes a 3 point arc there. (the start and end of the arc should be the first and last points selected)
ArcFitToPoints - as above for the input, but makes a best-fit arc, that is the start and and points may not actually be - probably won’t - the ends of the point sequence, but it may be a better approximation of the arc, I’d use the 3point version if you are pretty sure that the points selected fall on an arc.
Arc3PointFromPolyline as above for points but asks for a polyline as input - if you already have the arc-like polyline as its own joined polyline.
ArcFitToPolyline - as above for points only uses a polyline as input.
Arc3Pt.rhp (19.5 KB)
Not heavily tested but I think it works OK.