No problem Jeff, I'm glad to contribute to the mix! :)

Just to add one more wrinkle, there are also situations where it is not possible to extend an arc as a longer same radius arc and have it intersect the other object. That happens in cases like this:




The natural offset segments of these pieces look like this:




You can see there how the offset arc's radius is shrinking in such a way that the offset line does not intersect the arc's full circle anymore:





For trying to make a sharp corner in a case like this there is not much other choice than to extend both pieces by straight lines.

Anyway I believe once you start talking about extensions you are not really talking about a true offset anymore because the extension area does not have a constant distance to the closest point on the generator curve anymore.


> that said, I definitely don't think he'd find sketchup's solution acceptable as it doesn't
> return consistent distance even in the obvious (non corner) areas.

Well sketchup doesn't even have the concept of an actual curve in it right, only a bunch of line segments.

So when you try to offset an "arc" in sketchup you're not really in the realm of working with an arc, you're actually working with a polyline. A polyline has a tangent discontinuity in it at every single vertex, so it has this "what to do in the connecting area" issue all over the place.

If you want to do stuff with accurate arcs I don't see how that's going to happen in sketchup since it doesn't have any arcs there, only polylines...

- Michael