Selden's CMOD Billboard Meshes for Celestia

Selden's CMOD Billboard Meshes for Celestia



1.0: The Flat CMOD Billboards.

2.0: Using the Billboards.

3.0: Problems with the Flat Billboard.

  1. CMOD billboard model files cannot be displayed by any 3D modelling program other than Celestia.

  2. A problem in Celestia v1.3.0 (and later) is that Nebula models are not depth sorted. Instead, they are drawn on your screen in the order that you define them or in the order that Celestia happens to read their .DSC files. If overlapping Nebula models are declared in separate files. often they are drawn in the wrong order. When they overlap, you may not be able to see the one that is supposed to be closest to you. However, when you declare them in the same .DSC file, the model that is declared first in that .DSC file is drawn first, the second one is drawn on top of the first one, etc. At least that way you have some control over which ones are visible from a particular viewpoint.

  3. When you GoTo a flat Billboard object, Celestia sometimes overshoots. I suspect the extreme thinness of the model may be confusing it. If it thinks you are inside an object, various parts of the model get clipped off. In some cases, the whole thing will be invisible. Typing a "C" (center) or "T" (track) command and then backing away from it usually makes the billboard visible again.

  4. In the past, another difficulty for me has been getting the correct values for the Axis and Angle directives so the billboard is properly oriented and face-on to the line-of-sight from Earth. Grant Hutchison was kind enough to create a spreadsheet which calculates the correct orientation angles for most models. Also, a recent insight made it much easier to do positioning manually. The details are a little too complicated to go into right here. See 6.0: Aligning Pictures and Objects below.

4.0: Some Background.

5.0: Some Flat Examples.

6.0: Aligning Pictures and Objects.

7.0: Some 3D Billboards.