taskGNU Astronomy Utilities - Tasks: task #15892, Search VizieR datasets that cover...


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task #15892: Search VizieR datasets that cover a certain location

Submitter:  Mohammad Akhlaghi <makhlaghi>
Submitted:  Fri 22 Jan 2021 05:18:13 PM UTC
Should Start On:  Fri 22 Jan 2021 12:00:00 AM UTC Should be Finished on:  Fri 22 Jan 2021 12:00:00 AM UTC
Category:  Query Priority:  5 - Normal
Item Group:  Enhancement Status:  None
Privacy:  Public Assigned to:  None
Percent Complete:  30% Open/Closed:  Open
Effort:  0.00

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Wed 10 Mar 2021 08:59:17 AM UTC, comment #6: 

I fixed the box option and solve the units in the program, now it works with the same units in all options[degrees].

Thanks a lot Francois.

Adrián Hernández Padrón <adrihp06>
Tue 09 Mar 2021 12:32:54 PM UTC, comment #5: 

Boxes are defined with the parameters -c.bd= (degrees) or -c.bm (arcmin) or -c.bs (arcsec), e.g. -c.bd=1x3 (rectangle of 1x3°) or just -c.bd=1 (for a 1x1° square).

For simple queries to vizier, and a short list of parameters, the GET method (with urlencoded parameters) is shorter and simpler than the form (--form); the GET message may alternatively be transmitted by appending the question mark and parameters separated by an ampersand to the remote server. Example:

curl "http://vizier.unistra.fr/viz-bin/asu-tsv?-c=123.45+54.321&-c.bd=1&-ucd=src.redshift"

is identical to

curl -G --data-urlencoded -c=123.45+54.321 --data-urlencoded -c.bd=1 --data-urlencoded -ucd=src.redshift http://vizier.unistra.fr/viz-bin/asu-tsv

Replacing the --data-urlencoded by --form (and removing the -G) generates a form, which is much more verbose.

If you would like to see the actual differences, I've a very simple script as http://www.ochsenbein.org/cgi-bin/Echo which shows exactly what is received, e.g. try

curl -G --data-urlencoded -c=123.45+54.321 --data-urlencoded -c.bd=1 --data-urlencoded -ucd=src.redshift http://www.ochsenbein.org/cgi-bin/Echo


curl --form -c=123.45+54.321 --form -c.bd=1 --form -ucd=src.redshift http://www.ochsenbein.org/cgi-bin/Echo

Francois Ochsenbein <fochsenbein>
Mon 08 Mar 2021 08:23:38 PM UTC, comment #4: 

I made a commit adding the target and the radio/box option. I also add the curl with the ucd columns list and a format option for the output.
I have doubt about the curl from the box type, I use --form -c.br because was the only option that download data but I don't know if it correct.
I also update the help panel I recommend reviewing it before using the program.

Adrián Hernández Padrón <adrihp06>
Sun 07 Mar 2021 07:24:19 PM UTC, comment #3: 

Just 2 remarks:

1) Would be useful to allow a target, not only via a FITS image, but also as a target parameter -c= which can be a circle (-c.r) or a box (rectangle: -c.r), following the ASU convention at
http://vizier.u-strasbg.fr/vizier/doc/asu.html (almost 25 years ago!). The box is aligned with the coordinate system (no tilt angle) therefore it's not as accurate as the descriptor of a FITS image, but it can still be useful, I guess.

2) The list of UCDs in VizieR can also be accessible with
curl "http://vizier.u-strasbg.fr/viz-bin/asu-tsv?-source=METAucd"

[ As a general rule, all elements describing the vizier tables (the list of "META" tables) can be accessed from
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=META ]

Francois Ochsenbein <fochsenbein>
Wed 03 Mar 2021 07:54:22 PM UTC, comment #2: 

Adrian has written a first implementation for this job (focusing on redshifts within each catalog) in this respository.

I will try to test it soon and hopefully take the core command into  'astquery' to easily use with all the other aspects. Until then, if others get to look into it, try it and and provide feedback it would be great ;-).

Mohammad Akhlaghi <makhlaghi>
Group administrator
Wed 17 Feb 2021 12:13:37 AM UTC, comment #1: 

Adrian Hernandez Padron recently found another way to limit the queried datasets to only those that have a redshift column:

curl -oz-meta.tsv --form -c=23.4621+30.66 --form -c.rm=5 --form -ucd=src.redshift http://vizier.unistra.fr/viz-bin/asu-tsv?-meta

After a search, I found the The UCD1+ controlled vocabulary (PDF) which describes all such columns.

François, is there a way to apply such a constraint in the TAP interface?

Mohammad Akhlaghi <makhlaghi>
Group administrator
Fri 22 Jan 2021 05:18:13 PM UTC, original submission:  

VizieR is a very large database, containing many datasets. But most of the datasets only cover a portion of the sky. So when a user is interested in a certain part of the sky, it is very helpful for them to be able to limit the list of the datasets based on their covered position.

Doing this type of query based on the standard TAP features is not trivial. However, Francois Ochsenbein kindly noted that it is possible with ViziR's non-TAP interface with a command like below (for example to find catalogs within 5 arc-minutes of the RA,Dec coordinates of 23.4621, 30.66)

curl -oout.tsv --form -c=23.4621+30.66 --form -c.rm=5 http://vizier.unistra.fr/viz-bin/asu-tsv?-meta

If we remove the '?-meta' part, all the matching rows within this  center and radius will also be downloaded, and it is possible to download in FITS format (when one extension per matched catalog, each extension containing the rows of that table). However, this file can be large (because of all the data, for example the output above is 38Mb). So we only want the meta format here.

Currently in the 'meta' mode (which is what we want in this scenario) a FITS format output isn't supported. But the Tab Separated Value (TSV) output isn't hard to parse automatically. So we should add this feature for queries related to VizieR.

Mohammad Akhlaghi <makhlaghi>
Group administrator


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