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

[Akarsh Simha]

On Mon, Nov 14, 2011 at 09:25:57PM +0400, Alexey Khudyakov wrote:
> 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...

Hmm, that sounds interesting.

So you suggest that we can get away with computing Alt / Az and
precessed RA / Dec on-demand, since they are not really required for
drawing.

That sounds like an interesting idea.

Regards
Akarsh