shortcut to equirectangular image on sphere

Support Modeling
1

I recently stumbled across a shortcut to map an equirectangular image onto a sphere. It is exactly the reverse of the “traditional” way I have usually seen.

  1. Create a UV sphere as a model if you wish.
  2. Create a cylinder with the same number of segments and rings that you want. Leave top and bottom open.
  3. Make a vertical seam, probably in the back.
  4. Select all faces and simply “unwrap” onto equirectangular image. Scale/move to fill it.
  5. Scale and move cylinder vertices into sphere positions (model is helpful). You can discard the model.
    Takes only a few minutes and is very accurate. Unwrapping a UV sphere and editing takes forever.
2

What exactly takes forever?

  1. Add UV Sphere
  2. Delete bottom half
  3. Select top vertex, snap cursor to it, delete vertex
  4. Set pivot point to ‘3D Cursor’, extrude top loop, scale 0
  5. Mirror the mesh using whatever method you prefer
  6. Front orthographic view, Unwrap -> Sphere Projection
  7. In UV editor, switch to face selection mode and select one rectangular face
  8. In 3D view, Unwrap -> Follow Active Quads, OK
3

Thanks, I will dig deeper.
The tutorial(s) I saw moved all the vertices around by hand. Obviously there are better ways. There are lots of important tricks to UV mapping, not always obvious.

4

Import image as a plane (image should be 2:1, 1024x512 e.g. ); i assume you’d want shadeless material - set it in import parameters before import.
Loopcut so that there are two square faces. Subdivide all 10 or more.

Ortho view on shortest edge, place 3d cursor approx 2 BU under the middle of plane (Shift-S snap cursor to grid);
Warp 180 deg;
Ortho view on longest edge - Warp 360 deg. Remove doubles, invert face normals if this will be a new World.

Warp tool can be found on Space bar search.

5

Tried “Stan Pancakes” first, works quite easily and well. In step #7, it seems to matter which rectangular face I select. If on the bottom row, everything is fine; if I use another random one, top and bottom halves are shifted by one face for some reason.
I never would have figured this one out on my own.

Tried “eppo” second. Almost worked for me. When I select all vertices and remove doubles, the UV map gets triangular faces on a couple edges.

6

Ultimately, it doesn’t matter. After the unwrap is done you can just select everything and go UVs -> Pack Islands. Check the options (F6) afterwards, might need to untick “Rotate”.

When I select all vertices and remove doubles, the UV map gets triangular faces on a couple edges.

Well, don’t select all :slight_smile: Or deselect all the pole vertices before removing doubles.

7

Just to satisfy my curiosity - Stan Panakes, this method works beautifully, but why? When recreating top pole mesh by extruding and scaling 0, it gives back tri’s, but the UV map is quads? Strange. When I replaced the pole tri’s with quad fill, it worked, but not as elegantly as your method.

@techworker1 - how on earth does one manually move verts from a cylinder to form a sphere - lot of work involved there, I would think:)

8

edit: nvm.

9

They’re not triangles, they’re quads with one edge reduced to zero length.

10

Both methods seemed to sometimes give me tris at the pole holes (inconsistently). It confused me too. Basically things work OK, with a little extra noise at the poles.

This effort is trivial. :slight_smile:

  • Front ortho view, transparent, vertex mode
  • Box-select a ring of vertices, scale, slide vertically, repeat a few times
    Basically you should be looking at a model as your background.
11

They’re not triangles, they’re quads with one edge reduced to zero length.

Cunning!

This effort is trivial. :slight_smile:

  • Front ortho view, transparent, vertex mode
  • Box-select a ring of vertices, scale, slide vertically, repeat a few times
    Basically you should be looking at a model as your background.

Or shrinkwrap it?