UV mapping and spherical projection

[Stephen Tarheel]

Guys and gals,

I have a question that has been bugging me for awhile: I'm trying to use 3dcoat to prepare planet maps that'll be fed into GIS applications, so they need the equirectangular projection - aka a spherical projection.  However to paint in 3dcoat I need to UV it.  I can get close (but still distorted at the poles).  I can accept this with a large number of polys on the sphere and do some reprojection tricks to fix the poles later (baking to an offset map)...but I'd rather not if there's a way to do it right in 3dcoat the first time.

 

Thanks for any help!

[Carlosan]

Hi 

Spherical projection is always tricky, try this steps.

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I find the results are best when islands best match the actual shape of the geometry. The closer you get to this the less stretching you will have.

For a sphere, I find this works best for me. A cube with sub-D at level 2 which is applied then corrected in Edit mode with the To-Sphere tool.

Then 

Or even better for less stretching. (however, more seams mean more chance for the lighting to show artifacts with specular highlights on normal maps).

[Ascensi]

@Carlosan  Spherical Projection is just not the same as splitting the UVs into beach ball islands.. I've tried this... I am working with animations and spherical projection allows the textures to flow and tile smoothly as if looking through a lens whereas the beach ball slices make the textures appear as if they are coming out of individual pizza slices.  In Stephen's case you are probably correct unless he has some texture with spherical distortion/stretching.

Even if you slice a sphere in half as two islands it's not a projection emulation. We would also need to orient the projection on YY or z axis on the model. Zbrush does this fairly well ignoring most of the topology but could maybe be improved as observed in the top and bottom. in this case texture stretching is required*  for optical effects.  I do have the latest beta of 3DCoat as of today but I don't see anything to do with spherical UV Projection. I'm not sure why the top and bottom didn't work but I would love to have a solution to fix this.

Edited September 24, 2020 by Ascensi

[digman]

One way and as always might not meet your specific needs. 

The below information should be enough to get you going in 3DC for the work.

Once you get your UV sphere created and uv unwrapped. Good to go for multiple worlds, moons etc..

The first part has to be ouside 3DC. 

Create a uv sphere as shown in this video. Follow along in what he does to the sphere and the unwrapping. 

You can finish completely in Blender or do what I did. I cut out the hole, got my uv uwrapped and finished transforming the hole vertices to near zero in 3DC in the retopo room. I added a few edges loops too.

Subdivide the model in 3DC if you need it but that would be according to the finished product needs.

3DC:

Use the Spline image tool in the texture editor to apply the image. You might have to adjust the width of the image. adjusting the width does not appear to effect the image when it is applied to the model.

Also you might need to flip your image before using in the spline tool.

It takes a little  practice to get the hang of using the Spline Image tool in the texture editor. 

Older Blender but can be done in the new version of course or other software.

Picture shows the result.  In the texture editor, looks messy as I have applied the image to the model.

The stretching of Alaska was in image itself I used. 

Second image is how I exported from Blender then finished up in 3DC, transforming the hole vertices to almost zero. This is not necessary if you finish the process in Blender of another piece of software.

[digman]

Forgot to mention. 

Set your color to white in your color palette to get the true colors of your image.

[digman]

I glanced at the thread again and if this is not what you are going for, sorry.

I did some work on the uv wrapped sphere to remove a little more distortion.  The little hole in Antarctica is I need to get the hole vertices closer to zero.

I used a normal map this time as well.

Picture compares 3DC Antarctica to a map of Antarctica.

 

[geoath]

10 hours ago, digman said:

Forgot to mention. 

Set your color to white in your color palette to get the true colors of your image.

alternatively, to avoid color palette tinting your image, you can also disable (or enable) color palette with RMB click on color palette. Personally I didn't know that your method has the same result!