How to render shadow only?

[Digital Magic]

I have a CG road that I am overlaying on top of an image of a real road. I have an object passing over it that casts a shadow onto the road but I do not want to render the CG road, just the shadow on the CG road so that when I composite the animation onto the real footage the shadow appears on the real road.


How do I render the shadow on the CG road but not the CG object itself?
I have V-ray Next

[OPEN_RANGE]

I think use vray object properties for your road. Make the road a matte-shadow object from within the vray object properties dialogue. Check matte object. Set alpha contribution to -1. Check Shadows

I Need to do this only occasionally so some of my info may be off but I think that’s generally what you are asking for. Read the docs about vray matte-shadow Properties for more detail.

There is now the same matte-shadow options from Vray material wrapper in vray5. I have not yet used it but you could look at that also.

hope this may help

[Digital Magic]

Thank you very much! So easy if you know what to do.