i found some weird thing during learning UV-mapping: i created a plane object.
then i did the following sequence:
1.) go to edit mode
2.) subdivide 3 times. now i have a plane with 88 faces
3.) mesh -> UV-unwrap -> unwrap. Now i get an ideal uv map (88 squares, see pic 1)
4.) Now warp the mesh into a cylinder. i place 3D cursor below the plane, then
warp 360 degrees (W-360), so that the plane looks like a cylinder now.
5.) i locate the seem, where the left and the right side of the plane are wrapped together.
the seem is highlighted in pic.2 .
i remove double vertices now. and i end up with a perfect cylinder and a perfect UV-map.
everything is intact until here.
now trouble starts.
6.) I add one level of multires (either catmul-clark, or simple subdiv, it doesn’t matter for the effect). When i now look at the UV map, i see 16*16 squares as expected. But when i select the same vertex row in the cylinder, as before, i expect to select the vertices along the sides of the UV-map. But there is a sudden shift at the top 2 rows of the UV-map (see pic 3).
i tried everything to avoid this effect, but as soon as i add a level of multires, the effect apears (ok, in very rare cases the effect does NOT occur, but i was not able to tell, when that happens, and whn it does not happen). The effect only appears when i add multires, AFTER i have applied the Warp-tool.
If i apply multires to the simple plaine, the UV-map looks like expected,
but now i can’t remove the double vertices from point 5 (multires does not allow to remove vertices)
Anyone got an idea, what could cause this effect and how i could avoid it ? Yes, i know, there are simpler ways to get a perfectly unwrapped cylinder, but id like to understand my error.
thank you in advance.