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Re: match_2d [message #66190 is a reply to message #66183]

Wed, 22 April 2009 15:39

JDS
Messages: 94
Registered: March 2009

Member

>
> Aha... I've looked at it in gory detail, and it turns out that the
> routine implicitly assumes that the minimum value of both x2 and y2
> are 0. So you can get it to work if you do the following:

Aha! Thanks for the catch. That's what you get when you evaluate an
algorithm on artificial random coordinates ranging uniformly from
[0,1].

I've updated MATCH_2D at the address mentioned to handle this issue
explicitly, and also catch cases of matching points which fall just
slightly outside the bounding box of the search set. I've also added
a much-needed warning regarding using this Euclidean matching
algorithm for points on the sphere (e.g. star positions, lat/lon,
etc.):

; WARNING:
;
; Distance is evaluated in a strict Euclidean sense. For
; points on a sphere, the distance between two given
; coordinates is *not* the Euclidean distance. As an extreme
; example, consider two points very near the N. pole, but on
; opposite sides (one due E, one due W). For small patches,
; this Euclidean assumption is approximately valid, and the
; method works. See NOTES above for a tip regarding obtaining
; a (more) uniform match criterion on the sphere.
;;

Give this version a try. By the way, the value of MATCH_DISTANCE for
points which did *not* match is not meaningful.

JD

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[Message index]

		Re: match_2d By: vino on Thu, 23 April 2009 05:10
		Re: match_2d By: JDS on Wed, 22 April 2009 15:39
		Re: match_2d By: Jeremy Bailin on Wed, 22 April 2009 10:22
		Re: match_2d By: vino on Tue, 21 April 2009 09:23
		Re: match_2d By: Jeremy Bailin on Tue, 21 April 2009 08:47
		Re: match_2d By: Jeremy Bailin on Fri, 24 April 2009 10:50

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