Celestia Forums

Well... I know that my question seems very strange and maybe even silly

Is there any way to create in Celestia random lines (with various colors and thickness) between stars like the constellation lines or borders? I'm trying to use Celestia as a starmap where I can locate the sphere of influence of some fiction star states like the Minbari Federation (B5) or Clan's territory (BattleTech), or something else. It's very difficult to locate in space even the Rim - the edge of known space, - Periphery or fringe world without visible line. In Celestia the lines of constellation make a sphere looking (very rough, of course) like the Inner Sphere of BattleTech. Besides in Babylon 5 we may see the "hyperspace route" that connect two systems. It would be very nice if there's some way to create such lines.

Thanks for any advices or opinions ^_^

TutliQ,

Your question is neither strange nor silly.

In a future version of Celestia, it may be possible to draw lines in 3D space using a Lua routine call.

At the moment, however, the only options are either
1. modify Celestia's files of constellation lines and borders (asterisms.dat and boundaries.dat respectively; both are plain-text files)
or
2. create a 3D Nebula model which consists of lines between the appropriate positions in space. This method requires translating from RA, Dec & distance (or some other coordinate system) to Celestia's internal cartesian (xyz) coordinate system, and it requires some programming.

An example using such a model is shown below. It uses Celestia's ASCII CMOD model file format, and is available in the Alliance-Union addon available on the Web page at http://www.lepp.cornell.edu/~seb/celest ... index.html


(this links to a larger picture)

I wrote a Forrtan program to calculate the positions of the appropriate stars and hand edited the textual model file to draw the lines between them.

That's the kind of "layers" (or "custom classes") I want to add in Celestia : models of coordinate grids, lines drawn between stars, with labels, etc.

I would be very curious to see that famous "alien map" from the Betty Hills case, wathever what it is actually.

I was inspired by Selden's addon. So I made a small one, to draw a red line between our Sol and the nearest star : Proxima Cen.

Here's the DSC definition I'm using :


And here's the CMOD definition :


In the extra directory, just create a text file called "proxima.dsc" and paste in the content of the first code above. In a models directory, create a text file called "proxima.cmod" and paste in the content of the second code above. In celestia, you'll get a nice red line joining Sol and Proxima Centauri (after you turn ON the nebulae).

Also, create a text file called "proxima.cel" and paste in the code below. Use it as a script to mark Proxima. Fits very well with the red line.



I'm now tempted to draw some star maps using this simple technique, thanks to Mathematica.

I have used the asterisms.dat file to show routes between stars. The following image is from my website:


(I added the star labels with Photoshop)

bdm,

the problem with your approach is you can't change the lines color at will (two routes with different colors, say). And you're losing the standard asterisms.

bdm wrote:(I added the star labels with Photoshop)

Cheater !

Cham wrote:bdm,

the problem with your approach is you can't change the lines color at will (two routes with different colors, say). And you're losing the standard asterisms.

I posted the illustration to show the effect of changing the asterism file on its own.

I can change the colours if I wanted to, using Photoshop. If someone wants to set the line colours within Celestia, that is somewhat more difficult. Using the asterisms file, one can have Celestia use any colour one wants, so long as it's purple.

I also have the standard asterism file backed up if I need to use it.

bdm wrote:Using the asterisms file, one can have Celestia use any colour one wants, so long as it's purple.

???

Cham wrote:

bdm wrote:Using the asterisms file, one can have Celestia use any colour one wants, so long as it's purple.

???

Any customer can have a car painted any colour that he wants so long as it is black.
--Henry Ford (1863-1947), founder of Ford Motor Company

Here's a fun star map. Can you recognize what this is ?

Just copy-paste the code below into an ascii CMOD file, and use the same DSC code as defined above.

Wow! Thank you I'll try to do it right now.

selden wrote:TutliQ,

Your question is neither strange nor silly.

In a future version of Celestia, it may be possible to draw lines in 3D space using a Lua routine call.

At the moment, however, the only options are either
1. modify Celestia's files of constellation lines and borders (asterisms.dat and boundaries.dat respectively; both are plain-text files)
or
2. create a 3D Nebula model which consists of lines between the appropriate positions in space. This method requires translating from RA, Dec & distance (or some other coordinate system) to Celestia's internal cartesian (xyz) coordinate system, and it requires some programming.

An example using such a model is shown below. It uses Celestia's ASCII CMOD model file format, and is available in the Alliance-Union addon available on the Web page at http://www.lepp.cornell.edu/~seb/celest ... index.html


(this links to a larger picture)

I wrote a Forrtan program to calculate the positions of the appropriate stars and hand edited the textual model file to draw the lines between them.

Is there a tutorial somewhere on how to do this?

Nope, sorry, no such tutorial currently exists for Celestia. You have to know spherical trig and how the astronomical coordinate systems relate to one another. There are quite a few Web pages which discuss generic transforms between cartesian and polar coordinate systems.

I certainly don't have time to write that kind of documentation. Maybe Cham has something?

selden wrote:Nope, sorry, no such tutorial currently exists for Celestia. You have to know spherical trig and how the astronomical coordinate systems relate to one another. There are quite a few Web pages which discuss generic transforms between cartesian and polar coordinate systems.

I certainly don't have time to write that kind of documentation. Maybe Cham has something?

That all sounds beyond my abilities anyways.

Cham wrote:That's the kind of "layers" (or "custom classes") I want to add in Celestia : models of coordinate grids, lines drawn between stars, with labels, etc.

I would be very curious to see that famous "alien map" from the Betty Hills case, wathever what it is actually.

Did that using the asterisms approach.



Here is the map I got the info from.

Reiko,

this map is exactly the one defined in my previous model (with some color variations).

As a small tutorial, here's how I find the proper ecliptic cartesian coordinates to build a CMOD file. First, I need the standard ecliptic coordinates of a star : RA (in degrees), Dec (in degrees) and Distance (in LY). The exact coordinates used by Celestia can be found in Celestia's database, in the file "stars.txt" (a large file available on CVS), or in the file "nearstars.stc". Then I apply the following formulae to get the cartesian coordinates :



The x, y, z numbers are then used in the ascii CMOD file. Here's the part of the CMOD which defines the mesh itself (you also need a material header, as in the example given in a previous post) :



The vertices line defines the number of points declared in the list (2, in the example given above). The first point has coordinates 0, 0, 0, which is our Sun. The linelist command line defines the color to be used (color number 1, in the example above, which is a color defined in the material header), and the number of points to connect (2 in the example). The list itself (0 1 in the example above) defines a connection between point number 0 (our Sun) and point number 1 (of coordinates x, y, z).

Once the CMOD file is done, you need to define a DSC file, like the one I gave in a previous post. This is important to orient properly the model in Celestia, since there's a difference between the equatorial coordinates and the ecliptic coordinates :



I hope this may help people to build their own CMOD file.

I made the lines using file "asterism.dat". The result looks rather good! It's exactly what I wanted. Thanks!

Cham wrote:
I hope this may help people to build their own CMOD file.

Thank you very much!

Cham wrote:material # 1
diffuse 0.4 0.2 1 # Asterism like blue
opacity 0.7
end_material

material # 2
diffuse 0.6 0.3 0.8 # Purple
opacity 0.5
end_material

I have a question, how do you get the color codes?

Reiko wrote:

Cham wrote:material # 1
diffuse 0.4 0.2 1 # Asterism like blue
opacity 0.7
end_material

material # 2
diffuse 0.6 0.3 0.8 # Purple
opacity 0.5
end_material

I have a question, how do you get the color codes?

Color is based upon R G B factors, instead of being 0-255 that is ususaly used in other applications, it is 0.0 to 1.0.

So Take Red that is 255,0,0 becomes 255/255, 0/255, 0/255 or 1.0, 0 , 0