Celestia Forums

Hi there,

i have the following problem. I am rebuilding a SciFi universe in Celestia. This Universe has a coordiante system which originates in the center Blackhole of the Milky Way. Our sun lies on the x-axis of the coordinate system.
I have so far been able to transform the coordinates fram the galactic to a Sun centered coordinate system. And from that i created stc-files to use with Celestia. The problem is that the stars don't lie where they should lie. Well that is clear, since my point of origin is different from Celestias.

But i don't know how to break it down from Sun centered to the normal Celestia coordinate system.
The SciFi universe has some real stars like "Vega" and others in it. The position data of these should be from around the early 1960's or of the 1950 epoch data.

Has anyone any idea how i could do this and what transformations are necessary? I want to "just" turn around the whole system as one, since i want the distances between the stars to stay the same. They don't have to absolute accurate, since it is only a SciFi universe, but it would be nice if stars would be near their descibed positions. And there are about 700 stars to turn.

Regards,

Guckytos

Gucktyos,

Unfortunately, my own abilities with 3D transforms are not very good. They're the hard part, although they're relatively straight forward if you understand matrix algebra. However, there's one simple confusion factor in Celestia that often causes problems:

In an STC file, the Right Ascension must be specified in degrees, not in Hours.

Does this help at all?

Nope this does not help very much Selden, but thanks for the try.

I converted everything so that it useable, but the problem is that the center of my coordinate system is smack dab in the middle of our sun i don't have a clue how to move/convert all the data i already have so that the center of coordinate system is now as normal on/in the earth.

Hope that clarified my problem a bit more.

Regards,

Guckytos

The origin of the coordinate system should be at the center of the sun. Next you probably have to rotate it so that 0 degrees in the horizontal plane points toward the vernal equinox, and then tilt it so that the "north-south" axis is parallel with the Earth's. Or maybe the other order would be easier.

I made an excel97 spreadsheet that converts RA/Dex/Parallax into galactic co-ordinates - the XYZ co-ordinates given there are relative to the sun. Would this help you at all?

Thanks for the effort guys.

I will definitely try everything out. The trouble is here at work i don't have Celestia (i don't know why ) and my PC at home decided just now to develop some hickup with the net, so that i am a bit slow at responding to your suggestions and questions.
Sorry for that.

At Evil Dr Ganymede:

I downloaded your spreadsheet, nicely done. But my problem is the other way round.

So okay here again what i have with some examples.

I have an original coordinate system (OCS) with its point of origin in the central black hole in the middle of the Milky Way. From this goes the x-axis right trough the middle of SOL (our sun), which is at a distance of +30,000 LY from it. Now i just moved the point of origin from the OCS to the middle of our sun, so that i have now a SCS (sol coordinate system).
From there i have some values for real stars, both in that SciFi universe and in the real world.
Here are some example values all in LY:
Altair: x: -10.9 y: -12.1 z: -2.6
Arneb x: 131.3 y: 114.2 z: -2.6
Bellatrix: x: 230.7 y: 70.5 z: -69.2
Sirius: x: 5.9 y: 6.3 z: -1.4
Vega: x: -9.5 y: -23.5 z: 9.2

The SCS is in the following way: positive x-values are facing away from the center of the galaxy. Positive y-values are to the right of the x-axis (viewed frontal) and the positive z-values face upwards.

Since i din't have any real clues what to do, converted the x,y, and z coordinates into RA, Dec and Distance values through trigonometrie. Then i assigned the part of the x-axis that pointed into the direction of the black hole the value of RA = 270 (still in SCS).
After that i adjusted the RA to the value of SGR A (our real black hole in the Milkyway) by turning the whole coordinate system until my SCS axis and this were the same. And then i tilted everything by -29..... degrees to accomodate for the real position of SGR A.
So after what i thought i should now have mapped my original SciFi x-axis onto the axis connecting the sun with SGR A and by doing that the SciFI universe onto its "real" coordinates.
ANd all the RA and Dec i got from that where put into the stc.

But somehow this isn't so. So where did i err??

Regards,

Guckytos