Impact of Transparent Ceilings and Objects (Null BSDF) on Coverage Maps in Indoor Scenarios

[steffenitely]

Hi everyone,

For the visualization of coverage maps in indoor scenarios, I want to use the rendered 3D images with the coverage map (CM) and avoid using the 2D image that cm.show() gives me. Since my scene is indoors, I use transparent (null BSDF) materials for the ceiling and other objects near the ceiling.

I noticed that when opened with the preview function, I don't encounter any problems, and the CM is perfectly visible. However, when the same shot is rendered, the invisible objects near the ceiling (including the ceiling itself) obstruct the view of the CM. This makes the rendered 3D images of CMs for indoor scenarios unusable. The pictures below make it easier to see what I mean:
Preview of a custom scene with CM and invisible objects near the ceiling:

Rendered image of the same scene:

The invisible ceiling was not added in this scene, because otherwise, the whole CM would not be visible in the rendered image.

Does anyone know if there are any current workarounds or solutions for this problem?

Edit: One workaround is to first simulate the CM with the invisible ceiling/objects. Then load the same scene without ceiling/objects and finally render the CM inside the new scene in order to avoid the visual bug.