A (not so) Brief Introduction to Celestia Addons Part 6 (3rd edition)

0:  Introduction.
1: General Overview.
2: A Simple Addon.
3: A Simple Nebula Addon.
4: Installing a Complex Nebula Addon.
5: Installing an Addon of Stars and Planets.
6: Common Addon Problems.
7: Installing Celestia.


Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.


---

See also:
• Addon Intro in one page
• Selden's List of Resources for Celestia

Here are some of the most common problems I've seen:
1. Nebulas are invisible because Galaxy drawing is disabled (Celestia v1.3.2 or earlier)
   Solution: Type the letter "u" a few times. This should turn the Nebula picture on and off again. The Nebula and Celestia's grey galaxy blobs will always be visible at the same time. If you can't see the grey galaxy blobs, you won't be able to see any Nebulae, either.
2. Nebulas are invisible because Nebula drawing is disabled (Celestia v1.4.0 or later)
   Solution: Type a caret "^" a few times. This should turn the Nebula picture on and off again. Nebulae and Galaxies are selected separately in v1.4.0 and later. If you're using a European keyboard which supports diacritical marks, you'll probably have to type a space " " after you type the caret.

3. Spacecraft and Nebulas are invisible or planet surfaces are blank because the Addon's catalogs are in an \extras\ folder. This causes Celestia to look for the models and textures in the wrong places.
   Solution: Move the catalog files out of that \extras\ folder into the Addon's main folder.

   For example, all of the files that are in \NGC2237\extras\ must be moved into \NGC2237\ itself. Then delete the now-empty \NGC2237\extras\ folder.

   Originally Addons had to put their files in among the files that come with Celestia. The Zip file of one of these older Addons contains an \extras\ folder which corresponds to Celestia's own \extras\ folder. It contains the Addon's catalogs. Celestia v1.3.0 and later is confused by this and will look in the wrong place for the models and surface texture images.

4. Spacecraft and Nebulas are invisible or planet surfaces are blank because there are spelling errors in the names of the directories.
   Typographical errors are annoying. I don't know how many times I've stared at a file or directory name and not noticed that it's speled wrong.

5. Spacecraft and Nebulas are invisible or planet surfaces are blank because the image or model files are in the wrong directories.
   My hand-eye coordination isn't the best. I often manage to drag them into a folder that's nearby, but not the right one.

6. Nebulas are invisible because "Limiting Magnitude" is set too low.
   Type the character "]" a few times to increase it. "[" will turn it down again. The Limiting Magnitude has to be 2.0 or more for Nebula pictures and galaxies to be drawn.

7. Objects defined with 3DS models are invisible because the model file is specifying a different surface texture image file name.
   If you have a binary file editor like HexEdit, you might try editing the 3DS file to find out exactly what texture it's looking for. You could try changing it to use another texture to find out if the problem is related to the image file.

   Also, if you're running Linux, the case of the letters in the file's name matters. The case of the letters has to be exactly the same in the 3DS file as is used for the filename itself. Linux is case-sensitive, but Windows is not. As a result, some Addons which work fine under Windows fail under Linux. It's safest to change the name of the surface texture image file(s) to be exactly the same as is specified in the 3DS model. It's essentially impossible to fix a damaged 3DS model, but easy to rename a file.

8. Spacecraft and Nebulas are invisible or planet surfaces are blank because your graphics card has run out of graphics memory.
   If your 3D graphics card has limited memory (32MB or less) then you have to be careful not to look at many other objects before trying to look at a new one. Celestia does not flush "old" images from the memory on the card. If there's no room, the surface texture pictures for the new objects won't be loaded. As a result, Nebula objects may be invisible.

   One possible workaround is to disable the "medres" planetary images provided with Celestia. The lores surface textures only need about half as much graphics memory. One way this can be done is to rename the folder \Celestia\textures\medres\ to be \Celestia\textures\nomedres\.

9. Spacecraft and Nebulas are invisible or planet surfaces are blank because their surface texture images have the wrong sizes.
   Solution: If you're creating a 3D object, Nebula or planetary map, you may have mis-sized its surface texture image. Celestia requires all surface texture images to be a power of two on a side: e.g. 1024x512.

10. Spacecraft or other 3D objects have weird holes in them.
    Solution: if you're creating a 3D object, make sure the "surface normals" all point outward.

    The "surface normal vectors" specify the direction from which the surface is visible as well as determining how each surface patch gets shaded by light sources. If the normal points away from the observer, Celestia will not draw that patch. Some 3D display programs draw all of the patches no matter what directions their vectors point.

Contents

0:  Introduction.
1: General Overview.
2: A Simple Addon.
3: A Simple Nebula Addon.
4: Installing a Complex Nebula Addon.
5: Installing an Addon of Stars and Planets.
6: Common Addon Problems.
7: Installing Celestia.


Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.

• Addon Intro in 5 separate pages (for use with Babelfish)
• Selden's List of Resources for Celestia

A.1: Signature.

This Web page is maintained by Selden Ball at Wilson Lab.

A.2: Admonishment.

Please send any questions, comments or corrections to seb@lepp.cornell.edu
Alternatively, you can post a message (anonymously or otherwise) on Celestia's Web Forum or use its Private Message page.

If you don't tell me that something's missing, unclear or wrong, I can't improve it.

A.3: Disclaimer.

The author disclaims all liability and endorsement.
Copyrights may apply.
For details, please read the full text of his disclaimer.