Render transparency - shadows only

Rendering
1

Hi all,

In Rhino Render, I can set the Ground Plane to be transparent so that it only receives shadows, without rendering the plane itself.

Is there a way to do the same with a custom object or plane? For example, a vertical plane oriented along the XZ plane, like a wall.

In other words: can I make an object receive and show shadows, while the object itself remains invisible in the render?

Thanks!

image
image1920×1080 37.8 KB

RenderShadowsOnly.3dm (2.3 MB)

2

Not in the current state.

But for any plane just orient your items (including lighting) on the ground plane and use that, render out and rotate your render result in an image editing software.

3

Thanks, that’s a useful workaround.

For my case, though, I don’t think it fully reproduces the result I’m after. When I orient the whole setup onto the ground plane, I don’t seem to get the same sun/shadow effect as I would with an actual vertical wall plane in the XZ direction.

The viewpoints are also hard to match, because orbiting/navigation behaves differently once the scene is reoriented. So I can’t really recreate the same wall setup and composition by rotating the render afterwards.

4

The sun is just an automated directional light, add one that would correspond to the sun directional light. I’m sure you can write a script to get the sun directional light, create a duplicate of that and rotate it along with your whole scene to be on the groundplane, do a render, undo the rotate and duplication. Something along the lines of:

  1. create sun direct light duplicate
  2. select sun direct light
  3. select all your objects
  4. determine which is your wall
  5. create a rotation matrix from your wall plane to world XY plane
  6. hide wall plane
  7. rotate everything
  8. call the -_Render command with all the settings you desire
  9. call -_SaveRenderWindowAs (or _SaveRenderAs, I forget the exact name of the command) with all the settings you want; at least the file name
  10. _Undo (the rotation)
  11. _Undo (the wall plane hiding)
  12. _Undo (the sun direction light duplication)

I’m sure that you or someone can write the script, or you may be able to use an LLM tool to generate the script for you.

If you give your wall a special name, or add a user string to the attributes through which to identify your wall object it shouldn’t be too hard.

5

Thanks a lot for your help.

Regarding the viewpoints, I suppose I can recreate this by adding a camera manually.

It would be a useful feature in Rhino to have the option of creating a custom ground plane, or a shadow-catcher plane, with an arbitrary orientation. But I understand that this is probably quite a niche use case.

6

Working around this by moving the camera with F6 does not really solve the issue for me.

When the object is oriented along the XZ plane, the view I need is easy to achieve. But when the object lies on the XY plane, it seems impossible, or at least very difficult, to rotate the camera laterally in the same way.

Any ideas?

Thanks!

7

I found a workable solution. If you select the object and then use 2-Point Perspective, Rhino seems to establish a much more intuitive pivot/orbit behaviour around the selected geometry. Orbiting then feels far closer to working on the XZ plane (e.g. mounted on a wall)., even when the object is oriented on the XY plane