RE: R-tree indexing, RA wrap and LISTENing

[Chris Albertson <chrisalbertson90278@yahoo.com>]

I'd be carefull nt to introduce a systematic bais in the data.
if you have a computer and a positional astronomy library doing
_exact_ calculations is no hard.  The "great circle" method is
not a big deal to computer.  Even doing it a million times is
not a big deal.


--- Patrick Wils <patrickwils@yahoo.com> wrote:
> 
> --- "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
> 
> 
> __________________________________
> Do you Yahoo!?
> Yahoo! Calendar - Free online calendar with sync to Outlook(TM).
> http://calendar.yahoo.com
> 


=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278@yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson@aero.org
  KG6OMK

__________________________________
Do you Yahoo!?
Yahoo! Calendar - Free online calendar with sync to Outlook(TM).
http://calendar.yahoo.com