[Kstars-devel] Quaternions & Co (was: Plans for threading in KStars)

[Alexey Khudyakov]

On 14.11.2011 20:25, Akarsh Simha wrote:
> What exactly do you mean by Cartesian Coordinates? All objects are
> stuck to the celestial sphere (KStars doesn't know distances to most
> objects, unfortunately), so you could certainly use Cartesian
> Coordinates, with unit norm. But isn't spherical coordinates simpler
> here? Also, we typically would want to be able to show the user
> Altitude and Azimuth of an object.
>
Well they aren't. Spherical coordinates have singular points (poles) and 
any nontrivial transformation require expensive trigonometry.
The whole idea is to avoid it.

We still can return RA/dec and alt/az. But they have to be computed. 
These calls became relatively expensive (read: do not use in tight loop) 
but they just fine to call once, twice, 100 times...

P.S. I finally started to write down my thoughts on this topic.