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

[Aleksey Khudyakov]

> 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.
>
Exactly. We can make one step further and store only equatorial (for
stars, planets, etc) or horizontal (zenith, satellites) coordinates. This
means that we have to store two set quaternions for drawing. One
for transforming equatorial coordinates and one for horizontal.

This means that we don't need to keep equatorial and horizontal
coordinates in sync anymore. Costly EquatorialToHorizontal call
optimizes to nothing. Code would became vastly simpler.

Again calculation of horizontal coordinates for sky point with
equatorial coordinates becomes costlier (+28 flops AFAIR) and
coordinate transformation becomes explicit (which is IMO good
thing)