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Using particle density from a separate pointcloud

 
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Ian McBean



Joined: 14 Sep 2013
Posts: 2

PostPosted: Sat Sep 14, 2013 10:44 pm    Post subject: Using particle density from a separate pointcloud Reply with quote

Holge,

I'm trying to add particle density from a separate point cloud into a 'volume box' to simulate clouds on top of/emerging from a cloud or fog bank and am struggling to understand how this might be done. A post of yours regarding god rays (which I'm not worried about) from a couple of years ago gives some clues:

"...Get a box with the area of the clouds and god rays
Get the particle shader tree from the point cloud object
... In the box, set the particle density shader to pick the particle data from the pointcloud
If you render, you should see the particles rendered in the cloud..."

Problem I have is getting the particle density from the point cloud into the render tree for the box. I've tried setting a scalar attribute via ICE in the box, but I'm not sure exactly what to pick; selecting 'density' from the material on the point cloud doesn't seem to work.

The overall effect I'm interested in is a fractally generated cloudscape (which I can do with noise and gradients) with added particle-based clouds within it to add interest.

Thanks in advance for any help you can provide.

Ian McBean
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schoenberger
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Joined: 02 Mar 2005
Posts: 3786

PostPosted: Sun Sep 15, 2013 12:54 pm    Post subject: Reply with quote

Hi

Please use the pick data from external object in the particle density shader.
The cloud needs to be exported into MRay, so it cannot be completely hidden.
Please check the render log for error messages.

It could be that you have to keep it visible for render, but disable primary, secondary, sahdow.... rays in the visibility options.
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Holger Schönberger
Binary Alchemy - digital materialization
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Ian McBean



Joined: 14 Sep 2013
Posts: 2

PostPosted: Sun Sep 15, 2013 6:45 pm    Post subject: Reply with quote

Holger,

Thanks for the prompt reply.

All working fine now - my particle cloud is sitting nicely inside my volume box - I'm getting some very nice fading effects + some self-shadowing.

I keep getting a warning message of '13 MB warn : Particle density: No instance defined!' when I change anything in the render tree, but it doesn't seem to interfere with the output.

It was indeed necessary to keep the pointcloud visible for rendering while disabling all the other visibility options.

Thanks again for your time.

Ian
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