OK Fletch, here is what I discovered. I got the material "Volumetric" in my list now. Like you said, in Sketchup material dialog, select a material (color) edit it and save as Volumetric. This part done. And this has nothing to do with the missing part of light beam. As long as the material isn't "Default", is OK.
Second, the bottom of the Volumetric box CANNOT overlapping with the "Floor" or the "Stage" of the scene. The Volumetric box have to be slightly above or under the "Floor" or "Stage" of the scene. And there is a difference when the Volumetric box is above or under. Related to camera position.
If the Volumetric box is under the floor or stage, and camera is outside the Volumetric box, it is absolutely no problem at all.
This was rendered with bottom of Volumetric box under the stage, camera outside the Volumetric box. Everything is fine.
- Test 001a.jpg (70.5 KiB) Viewed 6639 times
And this, the bottom of the Volumetric box under the stage, but the camera is inside the Volumetric box. Not OK. The stage blocked the beam.
- Test 001b.jpg (24.23 KiB) Viewed 6639 times
Now. If the camera is inside the Volumetric box, causing the missing part of the light beam, the bottom of the Volumetric box need to be above the stage, in order to get the full light beam. But then, the stage will not be visible after rendered.
Interesting eh??
I got your point Fletch, now I am creating only one box, which is the Volumetric box.
x