I have a large, noisy shaped ground plane that includes lumps, walls etc. all in one combined mesh.

I'd like to receive shadows on this object, but not cast or catch shadows from itself. Is this possible with light path expressions, or render geometry settings?

Setting its render visibility to primary will mean it won't cast shadows, but will still receive shadows.

Or -shadow also works if you want it visible in indirect See render visibility here: https://www.sidefx.com/docs/houdini/props/karma.html [www.sidefx.com]

mestela
Setting its render visibility to primary will mean it won't cast shadows, but will still receive shadows.

Right! So it does. I was getting very mixed up, as I had already tried this, but what I was actually seeing was shadowing from an overall very soft dome light. I assumed this was shadowing coming from the ground object itself.

Thanks for clearing this up for me!

protean
Or -shadow also works if you want it visible in indirect See render visibility here: https://www.sidefx.com/docs/houdini/props/karma.html [www.sidefx.com]

This is also a super handy page of info, not just for the shadow tips. Cheers!

mestela
Setting its render visibility to primary will mean it won't cast shadows, but will still receive shadows.

that's not the same as turning off self shadowing though, since such object will not cast shadows to any object and will also not appear in any of the secondary rays

protean
Or -shadow also works if you want it visible in indirect

this is closer, but it will still not cast shadows on any other objects

so it would still be handy to be able to turn off self shadowing only, but still cast shadows to other objects and appear in other secondary
or for that matter to be invisible to any specific secondary self hit
I guess what would need tracesets to be able to exclude self