How about rhino calls circles, arcs and other geometric entities by their name, instead of calling them all curves?
Because rhino itself is fussy about the way it treats them.
So, if I have an isocurve extracted from a 3D wheel for example, it looks like a circle, but rhino wont accept any snaps to its center and so on.
So it has to be changed to a circle either by creating a circle over it, or calling curve-to-arcs.
If this curve-but-not-a-circle is selected, along with another curve-that-is-a-circle, that I have created alongside it with the circle command, the command line says: “2 curves added to selection”
Now this is actually true in that they are both curves, but its not useful since, well, one is a circle and one isn’t….
Its like both tigers and squirrels are animals, but, although true, its not helpful to say there’s a couple of animals in the garage; rather you’d like to know one was a tiger before going in there to do the laundry or whatever…
Further, when dimensioning a 2D set of curves (derived in this example from the centerlines of pipes) rhino will allow the radius dimension command to dimension curves-that-are-not-arcs, so it knows where the center is, but it wont accept angular dimensions, returning “curve is not an arc” to the command line.
So a curve can be an arc, but not be an arc at the same time.
Further, if the curve-that-is-not-really-an-arc-even-though-rhino-knows-the-radius is converted to an arc via the command mentioned above, it can still be incorrect, as evidenced by the angular dimension looking at only part of the curve-that-is-now-supposedly-an-arc.
So you have to delete the not-really-an-arc and redraw the arc, using the arc command, which you can do with accuracy, since you can use the radius dimension center as reference, left over from dimensioning the not-really-an-arc-at-all….
So I vote for always calling anything that rhino thinks is truly an arc, circle etc by their proper names, to distinguish from the ordinary curves masquerading as phantom arcs.