[Kstars-devel] freeze date

[James Bowlin]

On Sat August 11 2007 12:37 am, Akarsh Simha wrote:
> Is it possible to include apparent magnitude as an index along with
> the HTM indices within this duration of time?

Akarsh, I was working on this when I got surprised by the announced 
feature freeze.  I dropped it like a hot potato and threw myself at
getting what indexing was already implemented ready for release.  Sort
of like hitting the gas when you look up and see the light turning 
yellow.

Trying to squeeze this in too would be like running a red light at
60 mph (100 kpm).

The asteroids are the next target for indexing.  They would be stored
in a <QHash Trixel, <QList AsteroidObject*>>.  In each QList the
asteroids would be sorted by magnitude.  We use a QList because
of the re-indexing.

They have to be re-indexed frequently both because their (ra, dec) 
changes with time and also because their brightness changes.

The only tricky part is to figure out how frequently they need to
be re-indexed.  Akarsh and I were working on figuring out the
maximum proper motion (arcsecs/year) and rate of brightness change
when I bailed.  The maximum change in magnitude is infinite (I think)
because the magnitude goes to negative infinity when the asteroid
and the Earth are on opposite sides of the Sun.  But the change in
brightness stays finite.

For asteroids with orbits that stay roughly between Jupiter and
Mars I had come up with a simple formula for the max change in
brightness:

  max ( dB/dt ) = 8 * max( B ) / year.

I used the product rule for derivatives and then took the max of
everything on the right hand side and then gave things limits
based on geometry and laws of motion.  I think a similar simple
limit could be made for the proper motion as well but we haven't
done it yet.

If someone wants to work on this, that would be great.  I can post
my work if you want to see it.  I'm not 100% certain it is right
but I think it is the right direction to pursue.  I don't want to
think about this very much right now because I want to concentrate
on 4.0.  Assuming the current indexing code makes it into 4.0 then 
indexing the asteroid is my top new-feature priority for 4.1.


-- 
Peace, James