Brainstorming session

[Image Complete]

Hello,

I would like to hear your ideas regarding a technical issue we have to solve.

We lately work on a project of a holistic renovation of two attached buildings plus a new pedestrian bridge which will connect these two buildings with a 3rd building across the steet.
We have been asked to create in 3d the renovated buildings and the bridge and compose them into real photos.
In order to recreate the same lighting conditions we have created, in simplified form, the buildings of the neighborhood. We have also created the building to which the pedestrian bridge will connect.

The problem we face is that the new bridge casts some shadows to the connected 3rd building across the street. We want to keep these shadows in order to add them on the real building which is an existing building and is part of the real photo we want to keep. I know the existance of Shadow Catcher, however, any related online available information talks about how to use it on simple planes. We also want the geometry of the simplified building to keep contributing to the GI of the scene.

I am not sure I explained the situation clearly so I am attaching some photos.



I know that the simplest answer could be to just paint some shadows in photoshop, but what is the legit solution to this, if for example we had to create an animation of it?
How would you approach it?

Cheers

[Juraj]

You can apply shadow catcher to pretty much any geometry. It just gets tricky the more interaction there is back and forth between visible geo and catcher. I know every time I used such complicated scenario it gave me a bit of headache, mainly because shadow-catcher keeps also GI, not just direct shadows.

[Image Complete]

What do you think of the idea of having a visible simple grey geometry for GI purposes and a simple plane few milimeters away with an invisible shadow catcher material?

Cheers

[Juraj]

Maybe I am misunderstanding or you are me, now I am not sure myself :- ) I don't think you need double object, I meant that shadow-catcher captures both GI and shadows which is nice but also often complicates things in more complex scenario.

[Image Complete]

Yeah my fault. I got what you said. My previous post was just an idea. It was not connected to what you wrote :D
I don't mind that Shadowcatcher captures GI. I might be ok with it. However, what I don't know is if objects with Shadowcatcher material on them contribute to scene's GI.
If I apply shadowcatcher to whole object of that tall building on the right, will it contribute to scene's GI?

Cheers

[Juraj]

Yeah my fault. I got what you said. My previous post was just an idea. It was not connected to what you wrote :D
I don't mind that Shadowcatcher captures GI. I might be ok with it. However, what I don't know is if objects with Shadowcatcher material on them contribute to scene's GI.
If I apply shadowcatcher to whole object of that tall building on the right, will it contribute to scene's GI?

Cheers

Yes absolutely, it does :- ).

[maru]

Sorry, I'm a bit late, but I think Juraj has already explained everything nicely:

Corona Shadowcatcher is intended for this exact scenario. You have a real-life footage (could be still or sequence) you want to insert some 3D objects on top of that sequence, and make sure that the real-life objects capture shadows, contribute to the GI, are visible in reflections, refractions, etc.

So if you would take your real-life footage, set it as your viewport background, model the real-life building, and assign the shadowcatcher material to it, then that 3D building would now catch shadows, generate GI, etc based on the 3D scene (lights, other objects) and the color information in it. That's a simplification, but basically the colors from the real-life footage would act as diffuse colors for the 3D model.