| Re: Matching Lats and Lons from two arrays [message #62126] |
Wed, 27 August 2008 05:49  |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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On Aug 26, 11:47 am, wilsona <awils...@bigred.unl.edu> wrote:
> I have 2 seperate arrays of Latittudes and Longitudes.
> CS_LATLON(0,4607) is one latitude array and dlat(192,139) is the
> other
> CS_LATLON(1,4607) is one longitude array and dlon(192,139) is the
> other.
> I want to index through each element in both CS_LATLON arrays and
> find
> which point(s) in the dlat and dlong arrays are closest.
> I tried using nested loops but that gave me 12 million+ loops which
> is
> too many for my liking. I now am trying search2d
> NUM_PNTS = N_ELEMENTS(CS_LATLON(0, *)) - 1
>
> FOR J = 0, NUM_PNTS DO BEGIN
> CLOSE_LATS = SEARCH2D(dlat, 0, 0, CS_LATLON(0,J),
> CS_LATLON(0,J), INCREASE=0.5, $
> DECREASE=0.5)
> lat1 = CS_LATLON(0,J) * PI / 180.0
> FOR K = 0, CLOSE_LATS DO BEGIN
> lat2 = dlat(K) * PI / 180.0
> d_long = CS_LATLON(1,J) - dlon(K)) * PI / 180.0
> DISTANCE = 10800.0 / PI * acos(sin(lat1) * sin(lat2)
> +
> cos(lat1) * $
> cos(lat2) * cos(d_long))
> ENDFOR ; K
> ENDFOR ; J
> This is not working they way I would like. Any suggestions on this
> would be greatly appreciated.
You might find WITHINSPHRAD in JBIU useful:
http://astroconst.org/jbiu/jbiu-doc/astro/withinsphrad.html
-Jeremy.
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