Shadows are not correct

I think I have uncovered a fundamental flaw with Sketchup’s shadows.
Basically I have 2 buildings on a flat site where building 1 is casting a shadow onto building 2 and the surrounding ground plane.
I want to determine the extent of building 1’s shadows on the ground plane when they are ‘reduced’ by building 2 (i.e. allowing for the vertical shadow creep up the side of building 2). So to do this, I have turned off ‘Cast Shadows’ to building 2 so that I only see the shadows generated from building 1.
What I am seeing is that building 1’s shadow is still being cast onto building 2 as expected, but the shadows on the ground plane are completely unaffected by the presence of building 2, so it is giving me incorrect results.
Am I missing something here, or is Sketchup calculating shadows on a plane-by-plane basis, rather than taking into account all objects within the shadow’s path?

Thus the shadow conditions at the time the draft is usually done just before and after the rendering automatically rendered shadow disappeared.
hope it is useful

I can replicate the behavior.
The cube being set to not cast shadows, SU treats the cube as if it didn’t exist.
Seems a bit odd, but then so does a shadow study wherein a building in sunlight casts no shadow.
What’s the point?

So the cause of this behavior may be that someone overlooked this slightly illogical combination while programming the shadow logic.

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Auckland Council have a requirement to show the building’s specific shadow impact on the surrounding area minus any existing buildings. Kinda strange, but unfortunately necessary.

That, and SU doesn’t calculate the phases of the Moon.
I’d wager some day, some building owner will claim some proposed structure interferers with their moon glow.

I suppose for such demonstrations one could paint the surrounding buildings with a translucent material.
A face bearing a translucent material won’t cast a shadow until the material opacity reaches 70%
A translucent material will not receive a shadow until opacity is 100%

Here the opacity is set to 69%

Geo, thanks for the suggestion, but the point is that I need building 1’s shadow to react to building 2 as if it did exist. Then the shadow on the ground plane should not be visible on the far side of building 2.

Perhaps a little sleight of hand would work.
Then again, this trick might not be so good for a complex model with several time scenes.

Here, a separate face (hidden edges) within the ground face has Receive Shadows turned off.

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