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RE: Minimum spanning circles and Voronoi diagrams
> -----Original Message-----
> From: Chris Albertson [mailto:chrisalbertson90278@yahoo.com]
>
You are saying just use the stddev number for the set? Yeah, but how do you
intelligently combine both the ra and dec error bars into one number? This
why I thought of the MEC, as using the radius to determine the amount of
scatter. And, if there is a significant difference between the circle
center and the mean position, then there must be outliers.
> I think you want to simply define a minimum angle threshold
> based on the error bars on the astrometry. 15 arcseconds
> worked for the Mk III.
Actually, I am. But, there may end up being lots of points, and I like
doing unusual stuff in code. Besides, with 100 points, you have 4950
computations. By computing the convex hull, I get small set of points. My
ulterior motive is learning. Which is why I joined the Tass group in the
first place :-)
>
> Near the equator why not just use SQRT(ra^2 + dec^2) with
> ra and dec in degrees to compute the distance. It's fast.
> You can cut down the search by first applying a simple box
> function
>
I'll have to take a look at this. Thankfully, there is an SLA perl module
Astro::SLA, so this would fit nicely with the rest of my stuff. Thanks for
the pointer.
>
> Or you could simply link to a good library like "SLALIB"
> and call the "DESEP" function and get an debugged, exact
> answer. This is in FORTRAN but I have a C wrapper library
> that makes using it easy from C. Works for me on both
> Linux and Solaris.
>
> http://www.starlink.rl.ac.uk/star/docs/sun67.htx/sun67.html#xref_
>
> the SLA library was recommended to me by people on this list.
> I agree now. You really need this if you are going to do
> anything connected with astronomical coordinates. It is the
> "standard" library that is in wide use. This problem is
> not hard but others are
> For example, pretty soon you may want to match catalog data
> that is in a different referance system or you need to precess
> the data to a diffent epoc.
>