When a closed curve which goes around a “cylindrical” surface is offset or extended, the results are not as expected unless the curve seam on the surface seam. (Case 1 below)
Also when a closed curve on a “cylindrical” surface which crosses the seam but does not go around the surface is offset the results are not as expected. (Case 2 below)
Version 8 SR31
(8.31.26104.8181, 2026-04-14)
Case 1 Closed curve goes around a “cylindrical” surface with a seam. The curve seam is not aligned with the surface seam. Note that the surface and curve are non-rational.
Circumferential Curve On Surface Fail DC01.3dm (2.0 MB)
OffsetCrvOnSrf and the result is:
This result has the correct offset curve embedded in the results, but not a a single curve.
Move the curve seam to align with the surface seam, OffsetCrvOnSrf and the result is as expected:
Same surface and curve. ExtendCrvOnSrf and the result is:
The result is not as expected with the original curve is embedded as parts in two longer curves.
Move the curve seam to align with the surface seam, ExtendCrvOnSrf and the result is:
The result is essentially duplicate of the orignal curve d but the structure is different so it is not an exact duplicate.
Case 2 A closed curve is on a “circumferential” curve with a seam. The closed curve crosses the surface seam and curve seam is not on the surface seam.
Closed Curve On Surface Fail DC01.3dm (2.0 MB)
OffsetCrvOnSrf and the result is not as expected.
Move the surface seam is moved so that the closed curve does not cross the surface seam, and OffsetCrvOnSrf the closed curve. The results are as expected, including when the offset curve crosses the surface seam.
