How to fix nParticles shadow problem with mental ray

When rendering particles or nParticles with mental ray for Maya, you will notice that the option to cast shadow has no effect on the render.
For example this scene have a group of objects and you will notice that the spot light with ray trace shadow is casting particle shadow on both cubes and tea pots.

The problem appear when we want to disable the nParticles shadow on the ground.
One would go to the nParticleShape node and disable the cast shadow under the Render Stats.

Unfortunately this currently not working in Maya 2011.

Workaround 1
Disable the particles shadows entirely by going to the nParticles node itself , under mental ray > flags and disable Derive From Maya.
This will give you the opportunity to use mental ray native flags. The obvious answer is to set Shadow to No.

However this will give us another problem, what if  we want nParticles to cast shadows on a certain object but not on the other.

Workaround 2
In this scenario , we will go the object that we don’t want it to receive shadow and disable the receive shadow option under render Stats of the shape node.

This will disable the shadow from self and other objects , but yet the nParticles is not fixed.

The fix would be going to the mental ray render settings under Quality tab > shadows and change the shadow type to Segments.

Now the shadow will respect the shape node options.

 

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