Texture not aligning

[Kjellis85]

I don't really know if this is the right place for asking such a question but I am banging my head against the wall here...

I am trying to draw some micro topographical features on the texture from photoscan using Zbrush. I am a complete novice at 3D-modelling software, so the solution to my problem might be fairly obvious to others. My problem is that after I import the OBJ and texture into Zbrush, the two won't align. As far as I have understood, I need to create a UV map for the texture, but the texture file from Photoscan doesn't seem to fit any of the options in Zbrush. I have tried flipping both U and V, but the texture won't align. How can I get the two to align? Is there any information on what kind of UV-map is used in photoscan?

I appreciate any and all advice

[FLuca]

you need to create UV coordinate for your model.
it can be done in photoscan when building the texture: the dropdown menu 'mapping mode' has several options (generic, orthophoto, ...).
each method will assign the model a different type of uv coordinate and the associated texture. the problem is that the generated textures can not be easily modified.
better option is to use zbrush which have a powerfull tool called UV Master.
but to do that you need to dramatically decimate you model (100k-200k max) and create polygroups to control the parts remaining together and optimise the area used in you image.
once you have UV coordinate on your model, you can import it back in photoscan an use the option 'keep uv' when building the texture.
I recommend you search for tutorials on these subjects (decimation, projection, uvmaster).

whatever the technique, zbrush is handling textures differently than other 3d software: V coordinate is inverted
in zbrush: import a texture and then click on the flipV button
outside zbrush: apply a vertical symmetry of your image with your preferred software

good luck !

[Kjellis85]

Thank you for your reply

I did manage to do a workaround without having to decimate the model. All I had to do was to create texture from polypainting before importing the texture. That way Zbrush created a UV-map identical to the texture from photoscan.

Actually, I am not sure it was a UV-map, but the texture created from polypaint had the same "shape" as the texture file from photoscan. In any case I got it to work on the full res model, which was what I needed.