I couldn't find a way to produce a rendering without background (I can use an alpha channel, of course), but with the shadows of the objects in the scene projected on an invisible plane. This is for image compositing.
Could someone solve this problem?
OK - I do it.
* Create a plane material and disable "double-sided" at the VfR material. Now, you can render the plane from the bottom view - you should see the shadow.
* Crop the image so that the rendered plane can be used as texture.
* Create a new material, set color complete black and set the previous rendered ground texture as transparency map.
Now, your ground plane should be show a shadow only, nothing more. Maybe you need a little bit fine tune the texture at photoshop.
Here a quick test - background is added in photoshop.
