[Kstars-devel] HTM questions

[Jan Kotek]

Hi James,
Thanks for references,  thants exactly what I needed. It will take me
some times to read that source, so now just quick reaction.

> > 2) get neighbours of trixel in defined distance (ie get all objects
> > in distance from point)
>
> This is done by creating an index of the objects.  For point objects,
> the index is an array (or hash) of lists of pointers to the objects.
> The trixels are the index of the array.

So if I understand correctly, there is no math function for getting
neigbourh trixels,  you are just using precallculated tables? I am
planing level > 10 with many items, it can be problem.

There are some comparations of Healpix versus HTM. In short: healpix
is 10x faster becouse it does not use trigonometry (slow sin and cos),
but just some sort of coordinate division.

http://www.google.com/search?q=htm+versus+healpix&ie=UTF-8&oe=UTF-8

I will propably switch, bcos sky indexing is crutial for my
application. I am using sql and there is risk that I will need to port
indexing algorthm to TSQL language. Healpix core is more simplier. And
I also like documented source :-)

Regards,
Jan