[Kstars-devel] Drawing comet tail patch

[Akarsh Simha]

Hi Charles

> I tried to find descriptions on the trajectory but failed. I think that
> the trajectory is calculated implicitly in some member function that I
> didn't notice. Could you tell me how can I find the information related?

[Your older patch works here, but I'm waiting for the fixed one, so
that I could commit and write a beautiful blogpost about it!]

Although I'm pretty sure you could derive the result analytically, I'm
guessing that it would be quite some work (or maybe, you could just
look it up - you wan't the equation to a conic section in 3-D space,
having the given orbital elements).

For the time being, you could try computing the derivative numerically
within KSPlanetBase::findPosition(), where you can ask where the comet
will be some time back and compute the tangent to the trajectory.

Maybe you'd want to look at Cartes du Ciel's source-code
[http://sourceforge.net/projects/skychart/] and see what he does.

Regards
Akarsh