Tips for unwrapping curved shapes?

[Ryno917]

Apologies if this isn't the right section for it since it's not strictly minifig related, but as this is the customization section with some resources for decals, I thought this was the most appropriate area for it.

I'm working on some custom decals for a MOC. Most of it is pretty simple, flat shapes and the like. I do want to do a full cover decal for one of the newer windscreen parts, and I'm trying to figure out the best method for unwrapping the curves of it to get an accurate flat pattern. A less-than-exact method could be to cover the physical part in tape, trace out the edges, then remove the tape and scan that to get a somewhat accurate unwrap of the part. Not convinced it'd be accurate enough for a cut sticker to properly meet up at the edges, though. I'm currently modeling the part in CAD to derive accurate dimensions from, but it won't really help when it comes to flattening the curves themselves as I don't think there's a method to flatten the surface. As far as I can tell it's not a compound curve so there should be a geometric method to flatten it.

From what I can tell, the curves are all constant radius in 2 axis, which is simple enough, but when the other dimension is at an angle to that flat face, is there a good method to derive the final curvature and angles from it? I was thinking of taking the CAD model into Blender and doing a UV Unwrap of the curved face in there, but there's no guarantee that it's not warped and it's very difficult to verify. I could try to figure out the resulting elliptical shape from the intersection, but my geometry skill isn't quiiiite there to figure out the exact angle of the flat sides at the tangent point.

Do you guys have any tried and true methods for getting a good dieline for edge-edge decals on curved parts?

[MAB]

I'd use multiple small decals if that is possible depending on the pattern.

[Ryno917]

I'm mostly just trying to figure out how to get an accurate template to draw the decals on; and I want it all one piece for continuity and general polish. I wound up just putting tape over the windscreen piece, getting it stuck down well along all the edges, and using the side of a pencil's lead tip along the edge to mark out the shape, then remove the tape, stick it flat on paper, and scan it in at full scale in high resolution. It's not perfect, but it's close. When I get a chance I'll print out the templates and verify that it's accurate enough. Wish there was an easier/more accurate method, but I can't find it yet.

Edited August 15, 2024 by Ryno917