Rhino 3D Tip: Single-Seam Unwrap for Low-Distortion UVs on Developable Surfaces

Use Unwrap to place clean seams on developable surfaces and get low-distortion UVs fast.

When your part is developable (cylinders, cones, ruled lofts), a single, well-placed seam typically yields near-perfect texture flow and predictable decals. Here’s a concise workflow that balances speed with control.

• Preparation
  • Confirm the surface is developable. Cylinders, cones, and ruled lofts are safe bets; complex double-curved forms are not.
  • Assign a simple checker material to visualize distortion. Aim for evenly sized, square checkers across the surface.
  • If you have a polysurface, ensure edges are clean and joined; avoid tiny sliver faces that complicate UV layout.
• Core workflow (Rhino Unwrap)
  • Select your object (surface, polysurface, SubD, or mesh) and run Unwrap.
  • In seam selection mode, pick one unrolling cut that opens the surface:
    • Cylinder: one longitudinal seam from end to end.
    • Cone: one seam from apex to the base edge (ideally at the least visible side).
    • Ruled/developable loft: a single generator seam that runs cleanly across.
  • Press Enter to unwrap. Enable packing with a small margin (e.g., 0.02–0.04) to prevent bleed in renders.
  • Open UVEditor to nudge islands if needed. Use Align, Straighten, and Pack to optimize space and orientation.
• Quality checks
  • Checker pattern should appear uniform with minimal stretch, especially near the cone apex and along seam lines.
  • If you see elongation, add a secondary seam in the least visible zone and unwrap again.
  • Keep islands orthogonal to help decals and labels align with model axes.
• Best-practice seam placement
  • Hide seams along edges, back faces, or in shadowed regions for render cleanliness.
  • Avoid branching seams on developable shapes—one continuous cut is usually best.
  • On cones, radial alignment around the apex minimizes checker pinching.
• When to use alternatives
  • UnrollSrf (or Squish for mildly non-developable surfaces) for pattern making and 2D fabrication.
  • ApplyCylindricalMapping or ApplyPlanarMapping for quick, procedural mapping on simple forms.
• Workflow accelerators
  • Keep a “UV test” material in your template for instant distortion checks.
  • Use MatchMapping to copy a proven UV mapping channel from a reference object to a new one.
  • For DCC handoff, ExtractRenderMesh and export OBJ/FBX, ensuring your mapping channel is included.
• Troubleshooting
  • Overlapping UVs after pack: add or adjust a seam and repack.
  • Uneven texel density: scale islands in UVEditor until checker sizes match across parts.
  • Small, sliver faces: consider MergeAllFaces (where appropriate) or remodel the surface to reduce fragmentation.

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