I am stuck and a little embarrassed.
I'm trying to implement this answer. I have a unit vector $w$ pointing in the direction of a radio source on the celestial sphere.
$u$ and $v$ are the two other, mutually orthogonal unit vectors that point east and north from that point, tangent to the sphere.
Without back-converting to R.A. and Dec or using trigonometry, is there a simple way to generate $u$ and $v$ vectorially?
Slide 38 here may or may not be helpful, I think my description is sufficient by itself.
SgrA_star
(which is what would be $w$), or it can be from somewhere else entirely. From any given $w$ I'm asking how to get $u$ and $v$ without going back to trigonometry. Can it be done using just vectors somehow? $\endgroup$