RE: R-tree indexing, RA wrap and LISTENing

[Patrick Wils <patrickwils@yahoo.com>]

--- "Creager, Robert S" <CreagRS@LOUISVILLE.STORTEK.COM> wrote:
> At what distance do you need the spherical operators over planar? 
> And would
> they be used often enough to justify their creation?  I don't believe
> they
> would be required for matching stars to each other (7 arcsec?).

For matching stars and for things like "all the stars within 5 degrees
of position x", the difference between spherical and planar is not
important.  In most cases, it doesn't even really matter whether you
use boxes or circles.  The most important thing to keep in mind is that
when comparing RA values at higher declination, one should divide by
the cosine of the declination:  1 degree difference in RA at a
declination of 60 degrees, is only half the distance of 1 degree in RA
at the equator.

Patrick


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