Direct control of .mtl file on .obj export

Rhino
1

How do the variables in a material definition relate to the Ka Kd Ks, etc. in an .mtl file when I do an .obj export?

For example, I want the color that I define to only be for Ka, with Kd and Ks being black. Also, I need Ns to be non-zero, I typically set it equal to 1. These settings are optimized for another program I put the .obj into.

It is tedious for me to make changes by hand. For example, here as an .mtl file that came from Rhino:

image
image274×745 47 KB

All the Ns are set to 0 by default. How does Ns correspond to the material definition?

2

Rhino doesn’t have a concept of ambient reflectivity (Ka). Diffuse and specular reflectivity (Kd and Ks) are supported.

Ns is the specular exponent. That isn’t something directly available in Rhino either. Maybe the Shine/Glossiness of a Rhino Custom material.

For further information on what .mtl is check out https://www.paulbourke.net/dataformats/mtl/

3

Interesting, thank you for the information. The main thing I try to avoid in the other program is specular reflectivity. It also works if I specify diffuse reflectivity only. What are the direct controls for these in Rhino?

4

Depends on the material used. If you use Rhino Custom material then make sure gloss finish is set to black and 0%, reflectivity set to black and 0%, and likely you want transparency also set to black and 0%. Also make sure that Fresnel reflectivity is not checked under the material’s advanced settings. That should give you a completely diffuse material.

5

Awesome, thanks!