Now go to Contours, enable contour rendering. Then click on contrast shader under custom shader.



Click on contour_contrast_funtion_levels in the mental ray material under contour contrast.



Set the settings like this in the attribues.



Now click on store shader.




Now click on contour_store_function1.



OK, now the camera.

Create a camera in the attributes make the environment background a lighter color so you can see the line. Under mental ray click on output shader.



Then click on contour_composite.



Now render!!

Hope you understood everything, if you or anyone have any qusetions just ask, and i'll be more then happy to help

Good luck!

Vedic