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# How create a Geodesic line on the surface of a cylinder?

Member Posts: 22 ✭✭
ⵊ am making a decorative bead and am using a Onshape document to give a clear picture of what the disign should be. It will be a jade bead with a silver inlay.

A GEODESIC is a term that ⵊ know from physics. It is the shortest path between 2 points on a curved surface. Think of the line that an airplanes path taces on the surface of the earth as it flies long distance.

I'm sure that im missing a super easy way to do this, but this is new ground for me.

Thanks for the help in advance ::D

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This is the pattern that will be engraved and inlayed

And it looks great from the front

But when viewed off axis the fact that is a (Euclidean) projection becomes clear

The warping of the lines is what ⵊ would like to normalize and "average" out.

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Member Posts: 2,365 PRO
I don't know of a super simple universal way to solve this, but in the case of a cylinder, I think you could just use the Wrap feature. The unwrapped curve would be a diagonal line for most of what you're sketching out. I'm not convinced that these would be true geodesic curves (they're actually helixes), but it might actually be what you want.

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Member Posts: 2,066 PRO
I'd also reach for the Wrap tool for this first.

I have another thought that isn't exactly what you're asking for, but is relevant enough that it could be helpful. Freeform Spline supports faces as references, so you can create a curve that's pretty close to following a surface, which you can follow up with a Projected Curve in "Curve-to-face" mode to pull the Freeform Spline to the face. The result is a pretty interactive way to draw a curve directly on any face. Here's an example part studio. In the gif below I check "Final" to edit the spline while still seeing the resulting projected curve. I think if you use this method with a 2-point spline (i.e. line) it should end up pretty close to a geodesic.

Evan Reese / Principal and Industrial Designer with Ovyl
Website: ovyl.io

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Member Posts: 2,365 PRO
I don't know of a super simple universal way to solve this, but in the case of a cylinder, I think you could just use the Wrap feature. The unwrapped curve would be a diagonal line for most of what you're sketching out. I'm not convinced that these would be true geodesic curves (they're actually helixes), but it might actually be what you want.

• Options
Member Posts: 2,066 PRO