[AstroPy] Cross matching two source lists

Sergio Pascual sergiopr at fis.ucm.es
Fri May 11 07:16:42 EDT 2012


Hi Thomas,

the algorithm, as described by Groth, tries to find similar triangles,
so it won't work well
in large fields where the triangles are not very approximately "flat".

2012/5/11 Thomas Robitaille <thomas.robitaille at gmail.com>:
> Hi Sergio,
>
> Thanks for your reply! So it looks like your algorithm only works for
> e.g pixel or arcsec coordinates, not e.g. longitude/latitude or
> ra/dec, correct? (since for spherical coordinates, even for a small
> field of view, the spherical angular distance is not the same as the
> euclidean distance, i.e. 1 second of RA is not 15 arcseconds except at
> the equator).
>
> For a small field of view, one could do a KDTree using (RA * cos(Dec),
> Dec), but I'm interested in finding an algorithm that works for large
> areas of sky.
>
> Cheers,
> Tom
>
> On 11 May 2012 11:10, Sergio Pascual <sergiopr at fis.ucm.es> wrote:
>> Well, I don't know if it's exactly what you are looking for, but,
>> after some discussion in this list I created a package that
>> implementsthe Groth algorithm for catalogue matching:
>>
>> A Pattern-Matching Algorithm for Two-Dimensional Coordinate Lists
>> Eduard J. Groth 1986 AJ 19, 5
>> http://adsabs.harvard.edu/abs/1986AJ.....91.1244G
>>
>> The code is here: https://bitbucket.org/sergiopr/gmatch
>>
>> Regards
>>
>> 2012/5/11 Thomas Robitaille <thomas.robitaille at gmail.com>:
>>> Hi everyone,
>>>
>>> I am looking for a Python package that can do arbitrary and efficient
>>> cross-matching of source lists, i.e. some kind of kd-tree that uses
>>> spherical rather than euclidean distances. Is anyone aware of such a
>>> package?
>>>
>>> Thanks,
>>> Tom
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy at scipy.org
>>> http://mail.scipy.org/mailman/listinfo/astropy
>>
>>
>>
>> --
>> Sergio Pascual     http://guaix.fis.ucm.es/~spr    +34 91 394 5018
>> gpg fingerprint: 5203 B42D 86A0 5649 410A F4AC A35F D465 F263 BCCC
>> Departamento de Astrofísica -- Universidad Complutense de Madrid (Spain)



-- 
Sergio Pascual     http://guaix.fis.ucm.es/~spr    +34 91 394 5018
gpg fingerprint: 5203 B42D 86A0 5649 410A F4AC A35F D465 F263 BCCC
Departamento de Astrofísica -- Universidad Complutense de Madrid (Spain)



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