Applying a Simple Cylindrical Projection onto a Object

Question

Question: I have a wavefront object that I have imported into blender, and a simple cylindrical projection that I am trying to apply to it. The cylindrical projection is mapped around the prime meridian with longitude 0 on the left & right edges.

How do I apply this mapping to the 3D model in Blender?

My Attempted Solution: I tried 2 approaches: UV mapping and texture nodes. Both of them have run into problems so far.

(1) I unwrapped the model onto my texture with the following settings, but I wasn't able to get the model to map "properly" onto the texture. Here is an example of what I ended up with: - this is with the settings:

Directions: View on Equator
Align: ZX
Radius: 1.000
Correct Aspect: Check
Clip to Bounds: Unchecked
Scale to Bounds: Checked

(2) I also tried adding an image texture node to my model (with the texture coordinate node). However, all the settings I chose have given me stretched lines. Here is an album of my "best" attempts:

Background: I am attempting to create a textured model of an asteroid in Blender using data from NASA's PDS SBN. Specifically, I am looking to replicate the version of Eros from the 3D Asteroid Catalogue (click "Grayscale" on the website to see the texture), but with Blender instead of ThreeJS.

For reference, the wavefront file I'm using is located here, and the simple cylindrical projection I'm using is located here (warning, large image file).

Have you tried to texture it directly with an environment texture? Depending on the axis conventions, you may have to rotate the texture or/and the mesh model. — lemon, Feb 19, 2020 at 11:14

lemon · Accepted Answer · 2020-02-20 19:01:59Z

8

You can use an environment texture in order to project on the mesh surface.

The environment texture is generally used for scene environment lightning, but it performs an equirectangular projection that seems to meet our need here.

Take the object output from the texture coordinates node.

Plug it into a vector mapping.

And plug its result into the env texture node.

Now we just have to handle what needs to be rotated in the mapping (it's a guess): here a rotation of 180 around X and a -1 scale for Z seem to correspond perfectly to the mesh.

They are little distortions on the left part, but all craters have found the good place, it seems.

The texture from the link in the question is not included as too large to be uploaded with the blend file:

Note: 'equirectangular projection' is also called 'equidistant cylindrical projection'

edited Feb 20, 2020 at 19:01

answered Feb 19, 2020 at 15:58

lemon

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1

$\begingroup$ And I was wondering why my texture is still stretched. Now I see :) Thanks for lesson :) $\endgroup$
– vklidu
Feb 19, 2020 at 18:15
1

$\begingroup$ Thank you, that is perfect! I believe the stretching on the left is a result of the texture map itself, as it is present in the 3D asteroid catalogue as well. $\endgroup$
– Taycan
Feb 20, 2020 at 18:42
1

$\begingroup$ Perhaps the 180 degree rotation is explained here sbnarchive.psi.edu/pds3/multi_mission/… $\endgroup$
– batFINGER
Feb 25, 2020 at 16:01
$\begingroup$ @batFINGER, yes 0 on left and right, not at Greenwich. $\endgroup$
– lemon
Feb 25, 2020 at 16:09
1

$\begingroup$ @batFINGER, remember this from Cegaton? blender.stackexchange.com/questions/52904/… but the asteroid is not spherical or cylindrical... or from Leon blender.stackexchange.com/questions/24043/… $\endgroup$
– lemon
Feb 25, 2020 at 16:58