Celestia Forums

I've just written code to return a quaternion in Galactic Coordinates given a quaternion in equatorial coordinates. I used a published matix rotation, the only matrix rotation to Galactic I could find.

I had assumed that I could use the observer:setframe() method to get the equatorial coordinates. Unfortunately, I've discoverd that Celestia only returns universal coordinates, no matter what frame it's in. And since Universal is specific to Celestia, my understanding is there is no published rotation matrix from Universal to any standard frame. (Is this correct?) I undertand why this would be true, since Universal is a position-based coordinate system, and most standard coordinate systems assume a fixed position.

To be clear, I understand equatorial assumes an Earth position.

I'd welcome any suggestions on this. Another way of putting this is, I want to rotate the vector in the vernal equinox's direction (universal's x direction) into the position and plane of the Galactic center. Ideally I want to know for any x, y, z coordinate in Universal, what is the direction and plane of the Galactic center. It may well be I have to do all the math on this, which is fine, but I want to make sure I'm not missing something.

Are the universal x, y z coordinates of the Galactic center known?

Henry

I was under the impression (perhaps mistaken) that Celestia's Universal coordinate system is equivalent to the ecliptic coordinate system.

I see what you mean. Ecliptic coordinates are measured from the Vernal Equinox in the plane of the Earth's orbit. You're saying that the Universal x-y plane is the plane of the Earth's orbit. That makes sense.

I know that the Galactocentric coordinates for Earth are (8000, 0, 5) in parsecs fixed in the plane of the galaxy. I guess what I need is a transformation from the Earth's orbital plane to the galactic plane while moving the Universal x axis to the position of the center of the galaxy.

If I knew the position of the center of the galaxy in Ecliptic coordinates (which I guess is what you're suggesting) I should be able to figure this out.

Thanks!

Henry