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@@ -36,6 +36,9 @@ Comparison of real raytrace (blue) with parabasal raytrace (orange).
 
 Equal sided prism with blue and red light being dispersed.
 
+![Isotropic GRIN medium](https://cloud.githubusercontent.com/assets/12564815/24837010/87ed06ae-1d2a-11e7-8794-bab44d618e4b.png)
+
+Grin material with coordinate system tilted against global coordinate system.
 
 ## Formulas