Offset irregular curve

Hi guys. I need help with the following situation. I have an irregular curve that come from a terrain elevation. As i need to process this in 3DP and CNC i need to be able to scale the curve accordingly, ive tried offseting the curve which seem to work up to some point but i get some missing sections etc. Is this the best way to achieve this or do anybody have other recommendation.

Greatly appreciated
offset curve.3dm (3.2 MB)

Offsetting is essentially a 2D operation based on either the curve plane or the active CPlane. Rhino has trouble offsetting non-planar curves that have kinks - like your polylines in this case - as it doesn’t know how to connect adjoining segments whose endpoints are not at the same height.

If you have the original terrain that these curves came from, one possibility is to project a copy of the curve to offset to the CPlane, offset the flat polyline - which is generally pretty reliable - then re-project the result to the 3D terrain…


this will not lead to an accurate 3d offset, if my brains works properly.
the 3d offset has a different relative plane distance, greetings from Pythagoras.

if its just for a model you can use CurveThroughPolyline with anything else than uniform which will also smooth your terrain polycurve into one curve which you then can offset as you did. if you need it accurate you can still project that back to the original surface. or if the terrain would be one surface only not a polysurface you could use OffsetCrvOnSrf.

No, only something like OffsetCurveOnSrf would do that and only if the curve is reasonably smooth and you have one single surface. Terrain models are generally chaotic meshes and his curve looks like it’s derived from that. Depending on what type of CNC operation you’re doing, a 2D offset may be all you need - it may not even need to lie on the surface if you are using it to limit a toolpath’s extents or are doing a projection machining operation.


Thanks guys. Let me explain a little further. I start with a terrain and a flat curve which i offest to the desired width based on the scale for the machine i will be using ( 3dp or cnc router ) then that is projected to the terrain.

From there i extrude that surface and flatten the bottom and i get the shape of the street. Lets say i scaled this for 3DP but then i want to route this in wood, i would need to do this all over again for each type os scale / fabrication. Im looking for a way to control the thickness based on the scale

Again i appreciate the help

Well, I’m still not really understanding what you want, sorry… If you scale the terrain and the curves at the same scale factor they will have the same relationship, just larger or smaller. That is to say if you offset the original curve one unit for example, and then you scale both the terrain and the original + offset curve by a factor of 10, the scaled offset will also end up as 10 units.


I’m sorry for the poor explanation.

You are correct if I scale them together they will retain the proportion, but since I’m doing different fabrication methods the thickness ( once it’s a solid I) need be modified independently.

Lets say this is a street and I scale it so the width of it would be 25mm and I cut this in wood. Then I want to 3DP this and scale it by a factor of 10. The thinkness now is 2.5mm which could be to thin, thus I need to thicken it.