OffsetCrvOnSrf - Issues with tight corners on sphere surface


what I want to do is model a curve in 2D, then wrap it around a sphere using _FlowAlongSrf and then offset that wrapped curve by a specified amount on the sphere. For that I use the command _OffsetCrvOnSrf. However I get some weird artefacts when my original curve contains tight corners. I put together a small example:

offsetcrvon srf_issue.3dm (233.6 KB)

As you see in the picture, the green curve which I generated with _OffsetCrvOnSrf is distorted at the corner. It seems like the curve is not trimmed correctly or something… I would expect it to look more like the blue curve. The blue one I generated just with _Offset on the flat surface, and then wrapped it around the sphere. The problem is that I have to have the same distance between the curves everywhere on the sphere.

In this example I could of course manually trim the green curve, but this is not possible in my real project since the curves are too complicated for that.

I’m looking for a solution or a workaround to offset my curve on the surface, so that it looks like the blue curve, but with all the points having the same distance on the sphere to the original curve.
I would also be happy with suggestions for a different commands, a different way to achieve this, or a way to automatically trim the excess curve-pieces on the green curve.


Hi Chritzel - Explode the green, trim the bits at the inside corner, delete the extras - I don’t think there is a better way at the moment for a case like this. You might try offsetting before flowing too.


Thanks for your answer - unfortunately it doesn’t help me much :confused:
As mentioned, my actual curves are far more complex than this example, and there are hundred of occurences of this happening. This goes to a point where the whole sphere is just covered by lines…

I guess what I could try is use a different shape for the surface I model the curves on - not a rectangle, but something a little more curved. Then I guess the differences in the offset distances would be less when I do the flat offset and flow after that.

Hi Chritzel - offsetting before you map the curves to the target surface does not help?


Hey Pascal,

yes it works - but then I have the issue that on the curved surface the
offset-curve does not have an uniform distance to the original curve due
to the mapping from the rectangular surface. So at the “equator” the
offset is larger than on the “poles”.

However I want to have an offset on the curved surface, which has always
the same distance to the original wrapped curve.

This obviously has a larger effect the nearer you get to the “poles” with the original curve. In this example this may not seem so bad, but some of my other curves go right by the poles.