shadow question

[emartin8907]

Hi,

I am wondering if it is possible to use a ground plane for a shadow without seeing the ground plane itself in the reflection of an object.

Please see attached pictures for reference. Red ball is what I have in Maya (see how the reflection ground plane is visible in the red ball as a white square). Blue ball is what I'm trying to get (from keyshot. notice no ground plane and no plane in reflection its just a transparent shadow. )



I am using the material wrapper shadow set up method and it is working for the alpha



I just don't want the ground plane visible in reflections/ blocking the hdri dome

[tashko.zashev]

Hi,

Have you tried to use the option Matte for all secondary rays available in the Matte properties roll-out ?

[emartin8907]

you mean in the material properties of the material wrapper? I just tested it and the ground plane simply shows up black in the reflection now instead of white.

Here it is with 'Matte for All Secondary Rays' off


Here is how it renders set to either 'With Projection mapping' or 'Without Projection Mapping'

[vlado]

Can you post your scene? This works fine for me generally.

Best regards,
Vlado

[emartin8907]

I had to delete the hdr because it made the attachment too big...

Shadow_Test.mb.zip

[bvoldm]

couldn't you assign a VrayObjectProperties to the ground plane and uncheck visible in reflections?

[emartin8907]

tried this but then the shadow is no longer visible in the reflections of my sphere. i am dong automotive rendering and want the car to look 'grounded' and have proper shading from it's own shadow otherwise it looks like its floating. I guess I could use an AO pass for this but I would really like for it to pick up its own shadow properly..

here it is with no ground plane:



here it is with ground plane Object Properties set to not be visible in Reflections and Refractions.


here it is with no object properties- notice the giant black shadow reflecting in the sphere? I want this but without seeing the rest of the plane.



notice how the blue ball in my original post is picking up its shadow over the reflection of the hdr dome- this looks much more realistic than no shadow. not even sure if ao pass will give me what im looking for really.

[emartin8907]

ooo what about this- bake the alpha and use that as opacity mask for ground plane?? Is this possible? I have no experience baking maps but this seems like a simple thing?


with Object Properties applied to the sphere and Primary Visibility turned off on it, here is the rgb and its alpha.

[bvoldm]

than how about unchecking "primary visibility" and leaving "reflection/refraction" on? that way the plane still reflects into the sphere but is invisible in the render. oh nevermind. than you won't see it in the render.

[yolov]

you mean in the material properties of the material wrapper? I just tested it and the ground plane simply shows up black in the reflection now instead of white.

Here it is with 'Matte for All Secondary Rays' off
[ATTACH=CONFIG]24875[/ATTACH]

Here is how it renders set to either 'With Projection mapping' or 'Without Projection Mapping'
[ATTACH=CONFIG]24876[/ATTACH]

This is because the matte returns the background environment. If you plug the same texture you're using for the dome light into the global environment overrides (render settings > vray tab > environment) you should get the result I think you're after.
The background is black by default and that's why the matte appears black.
And it's reflected as black in the sphere, because there is no global reflection override and black is used by default.
Using matte for secondary rays should also help on top of all the above.

[vlado]

Here is the scene modified with Alex Yolov's suggestions.

Best regards,
Vlado

[Algehov]

Correct me if im wrong, but It feels like this will only fix the issue if you are only using a hdri, which you map into background.
I've had this issue before, and never managed to solve it in a nice way, but instead of only have a hdri that I want reflections/lights/shadows from (then shadows being visible in the reflection) I projected an image onto geometry which I in return wants to behave in the same way. So It needs to be a surface which doesnt recieve light (as thats already baked in) and then returns the same values in reflections. But I still want it to recieve shadows, and having them appear in the reflections aswell.
I thought this was doable with a Matte Surface, but I've never got it to work.

Any idea on how to go about solving this? The projected geometry will not be rendered (or with black alpha). Its only there for more correct reflections and shadows. And sending off light I guess.

[vlado]

Any idea on how to go about solving this? The projected geometry will not be rendered (or with black alpha). Its only there for more correct reflections and shadows. And sending off light I guess.

Is that not what the matte ground plane is doing in the image above? You can map anything to it, not just the projected background, by adding V-Ray material override attributes to its shading group and then you can use any kind of map in its "environment" slot. (Just make sure to set the "matte for secondary rays" to "without projection mapping".)

Best regards,
Vlado

[vlado]

Take a look at the attached scene. Does it look like what you need? Instead of the checker, you can use any HDRI map that will be mapped to your geometry. If you don't need to see the geometry with the checker, you can turn off its primary visibility.

Best regards,
Vlado

[vlado]

Hm, there's also a "secondary matte" environment map to be used for matte objects in reflections, but it looks like we didn't expose this in Maya. Will make a note to add it. You can set it with a Python callback though.

Best regards,
Vlado