Celestia Forums

Celestia v1.3.2pre3 or later is required for this Addon.

Using Celestia's new CMOD model definition language, a new set of graticules have been created.

Their graphic pattern is very similar to the one used in my previous Graticules for Celestia. However, since these are drawn as lines in space instead of being surface texture pictures, their visual appearance is quite different. For example, their lines are all a constant size on the screen instead of being progressively larger for the larger graticule sizes.


See http://www.lns.cornell.edu/~seb/celestia/graticules.html for more information.


(This is a link to a much larger picture where the graticule lines actually are visible.)

I just zoomed out from the solar system to the 10 billion parsec graticule. Wow. Watching grid after grid after grid shrink to a point--each one representing an order of magnitude--really drove home the scale of the universe like nothing else in Celestia. I'm also impressed that Celestia handles such a wide range of graticule sizes so well (clipping bug excepted.)

--Chris

Nicely done Selden.

Chris, could it be possible to make and load/unload a model on the fly from a Lua script? I think that would be very useful for things like graticules.

selden, does this mean that the graticules can be toggled on an off?

Cool!

I haven't seen any other mention of the new model format anywhere else- where can I find out more? I looked at the format of Selden's graticule object, but obviously it wasn't typed out by hand... What programs can be used to edit it?

Celestia's new CMOD format is like 3DS in that it's just another way of defining a 3D shape. It's much more efficient because Chris designed it to match the data structures actually used in 3D graphics cards. Celestia's frame rate seems to be between 1.5 and 2 times faster when displaying a CMOD model than when displaying an equivalent 3DS model of the same object.

There really aren't any GUI modelers yet that can generate CMOD models. The squares in the graticule actually were done by hand when I realized that coding around the "fencepost" problems would take longer, but I wrote a trivial g77 Fortran program to generate the circles and fiducial marks. (I suspect Fridger would have used a perl script ) I understand that Chris has been using some conversion utilities, but I don't think they're freeware.

Sorry, I don't know of any way to turn CMOD models off and on at runtime. They're just like 3DS models in that regard. Facets can have normals and be invisible when you look at them from the wrong side, but the graticule consists only of lines -- I don't know of any way to associate normals with them. But I'm certainly no 3D expert.

Christophe has created a DOxygen Web page from the text in the new Mesh and Model source code files. It's at http://celestia.teyssier.org/source-documentation/classAsciiModelLoader.html

Bear in mind that this is still in beta test. Models created now might not work at all with future pre-releases or in 1.3.2 final.

I hope Chris doesn't mind, but...

I've added a section to my "cryptic Celestia Notes" page that includes some of the things he's written on the developers' mailing list as well as some of the comments from the source code which describe some of the features of the new model format. See http://www.lns.cornell.edu/~seb/celestia/celestia_notes.html#14.0

selden wrote:Celestia's frame rate seems to be between 1.5 and 2 times faster when displaying a CMOD model than when displaying an equivalent 3DS model of the same object.

And there are no seams or visible facets in the moon/asteroid models in this format, using exactly the same datasets!

Grant

Hm... Could be hard to get into this new format so... I hope somebody can come up with a converter once all the problems have been ironed out. Anybody know if the CMOD formal will allow things like animation, specular/normal maps on surfaces?

If this is outlined in one of the linked pages, you'll have to excuse me- it's 2:30am... Right so- I'm off to bed...

That is amazing Selden!

I'll have to go try the other ones too.

-Don G.