Matte/shadow catcher issue

[JCdeBlok]

I'm adding some 3d to a 360 panoramic photograph and I'm having trouble with the matte objects.

These object are there to generate the shadow that falls onto the CGI and maybe to bounce some light back onto the pavement and only that.  But I'm having a hard time making the matte objects themselves invisible, they seem to catch some light and I need them out of the equation with alpha=0. I could generate a mask render element but I'm hoping for a more elegant solution..

See attached images for problem and some relevant settings, any clues?

[maru]

Hi, basically you need an invisible object, which casts shadows? Optionally generates some GI?
I think you should use RaySwitch mtl with everything set to invisible (empty) except for GI, which should be set to CoronaMtl with pure black diffuse color - then you won't get any GI, but it will cast shadows.
Or you can plug the ShadowCatcher into the GI slot - then it should generate GI based on the backplate.

[JCdeBlok]

Hi, basically you need an invisible object, which casts shadows? Optionally generates some GI?

As silly as it sounds it quite a common requirement when mixing reality with cg! :)  It can get even worse if I add a 3d light source to the scene,  the matte object should catch that. If I add a 3d car with headlights in the street I want it to add light and illuminate the matte objects.

I'll give the suggestion a try, thx!

[PROH]

AFAIK the problem is, the Corona Shadow Catcher isn't a full blown matte/shadow material, but "only" a Shadow Catcher.

It would be extremely nice, if it was made into a full blown matte/shadow material, so we wasn't forced to use other render engines for this kind of everyday work :)

[JCdeBlok]

AFAIK the problem is, the Corona Shadow Catcher isn't a full blown matte/shadow material, but "only" a Shadow Catcher.

It would be extremely nice, if it was made into a full blown matte/shadow material, so we wasn't forced to use other render engines for this kind of everyday work :)

Indeed! I've put up a feature request here https://forum.corona-renderer.com/index.php/topic,10327.0.html

[selant]

In car renders, which contains an HDRI background, i need to put a simple plane on the ground to catch the shadows. It must be transparent. But i couldnt catch the result.
I tried to make with  RaySwitch mtl also, but i cant make it to be transparent. Any tutorials or ideas on this ? Thank you



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[selant]

I guess this video tutorial would help anybody interested :

[Nekrobul]

Just make you're plane bigger.

[Ludvik Koutny]

Yep, environment around the car casts quite long shadows, you just need to make your ground plane bigger so there's more space for shadow to be caught on.

[selant]

Yep the answer is sometimes too close or simple, but trying to figure out lots of parameters then i'm lost.. Bigger plane solves the issue. Thanks all.