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New VO Command-Line Tools -- Available for Testing

  • Tuesday, November 13 2007 @ 09:23 PM GMT
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A new set of tools for easily accessing Virtual Observatory data from the command-line (and thus scripting environments) is now available for testing. These tasks permit searching for VO resources and the query/access of image and catalog data from more that 15,000 sources. A key design point is the use of astronomer-friendly terms in specifying resources, general search capability (e.g. all X-ray image services), and a variety of output formats (default is CSV for easy manipulation by other tools).

The VO-CLI Project Home Page contains additional information, runnable examples, download instructions, as well as a guided tour of the software. These tools were developed as part of a larger VOClient project designed to provide a multi-language interface to VO data and services. They will be used in the upcoming IRAF NVO package but as host tools can be used from any environment. Examples of what you can do include: keyword searches to find relevant VO resources, process queries for lists of positions, easily find all HST data for a given object, or simply resolve and object name to its coordinates.

Since this is a testing release, feedback in the forums or comments is especially appreciated. Detailed examples of how to use the main data query/access task are shown in the main body of the story.

The following examples come from the VODATA documentation showing the many things that can be done with the task. Similar examples are available for the other tasks.

       1)  Query  the  GSC  2.2  catalog  for  stars  a) within the 0.1 degree
           default search size around NGC 1234:  b) around all positions  con-
           tained  in file 'pos.txt':  c) for the list of objects given on the
           command line:  d) query a list of services for a list of positions:
           e)  print a count of results that would be returned from 3 services
           for each position in a file:

                % vodata gsc2.2 ngc1234            (a)
                % vodata gsc2.2 pos.txt            (b)
                % vodata gsc2.2 m31,m51,m93        (c)
                % vodata svcs.txt pos.txt          (d)
                % vodata hst,chandra,gsc2.2 pos.txt     (e)

       2)  Query all (142) image services having data of the  subdwarf  galaxy
           IC 10, print a count of the results only:

                % vodata -c -t image any IC10

           Note  that  we use the reserved word 'any' for the service name and
           constrain by image type.  The task  will  automatically  query  the
           registry to create the list of services to be queried.

       3)  Print a count of X-ray catalog data around Abell2712:

                % vodata -c -t catalog -b x-ray any abell2712

           In  this  case  we  constrain  both the service type as well as the
           spectral coverage published for the resource in the  registry.   We
           use the reserved flag to print a count without saving results.  The
           object name is resolved  to  coordinates  internally.  (Note:  this
           example may take a while to run).

       4)  Print the column metadata returned by the RC3 catalog service:

                % vodata -meta rc3

           The  output  will print the result using the default VERBOSE level,
           adding the -v will set the query parameter  VERBOSE=2,  adding  -vv
           will  set VERBOSE=3 (to print all available columns).  When access-
           ing data the same -v flags will be required to retrieve columns  at
           that VERBOSE level.

       5)  Use  the  Registry  to  query  for resources using the search terms
           "cooling flow".  Upon examining  the  output  the  user  notices  a
           Vizier  paper  titled  "Cooling  Flows in 207 clusters of Galaxies"
           that looks interesting.  Use the vodata task to download all tables
           associated with this paper, save tables in the default CSV format:

                % voregistry cooling flow
                % vodata -O white97 -all J/MNRAS/292/419/

           All 7 tables will be written to the current directory to files hav-
           ing a root name 'white97' (chosen based on the author and  publica-
           tion date).

       6)  Find  a  suitable XMM image service, get a (brief) count of the XMM
           images available for 3c273, and if there aren't too many,  download
           the images and save the extracted access URLs:

                % voregistry -rv -t image xmm
                ShortName       ResourceType    Title
                XMM-Newton      SIAP/ARCHIVE    XMM-Newton Archive ....

                % vodata -cq xmm-newton 3c273
                  xmm-newton         27    I  XMM-Newton Archive ....

                % vodata -get xmm-newton 3c273
                   .... will query and download 27 images.

       7)  Query  for  the  images  available  from 2MASS at a given position,
           extract the positions and service URLs to separate files:

                % vodata -e -O 2mass -t image 2mass 12:34:56.7 -23:12:45.2

           The query produces files with the root  name  '2mass',  and  exten-
           sions  of  ".csv"  (the  main response), ".pos" (the extracted pos-
           itions), and ".urls" (the access references).   The  user  inspects
           the files and notices that the references return both FITS and HTML
           files, but she only wants the FITS image date and  uses  vodata  to
           download only those:

                % grep fits 2mass_I_001_15998.urls > images.txt
                % vodata images.txt
                % grep fits 2mass_I_001_15998.urls | vodata -i -

           In both cases we pass URLs to the task which bypasses the query and
           directly access the images.  However, in the first case we  process
           the entire list and are able to take advantage of the -md option to
           increase the number of simultaneous downloads.  In the second case,
           the  -i  flag  causes  the task to interpret each line of the input
           stream as a separate command and so the data are always  downloaded
           one at a time (which is the default download behavior anyway).

       8)  Use vodata as a test client for a locally-installed SIAP service:

                % vodata -t image -s http://localhost/siap.pl 180.0 0.0

           In this case we force the ServiceURL using the '-s' flag, but since
           we can't do a Registry query to discover what type of service  this
           is, we must use the '-t' flag to indicate it is an image service.

       9)  Create  a  local  table containing the Abell catalog.  Begin with a
           Registry query to find likely services using the  voregistry  task,
           print  a  verbose description of each resource and page the results
           with less:

                % voregistry -vv -t catalog abell | less

           The verbose results indicate a number of  services  with  differing
           requirements  for  what  is included.  We decide to use the service
           from HEASARC since it contains southern hemisphere  data  and  con-
           straints  we  are  interested in.  Try an all-sky query to retrieve
           the entire catalog, use the service identifier to be specific about
           where we want to go:

                % vodata -e ivo://nasa.heasarc/abell 0.0 0.0 180.0

           We  use  the  '-e' flag to extract the positions to a separate file
           with a ".pos" extension so that we can use these in later  queries.
           However, the .pos file additionally contains the ID from the origi-
           nal catalog in column 1.  Strip this column so we're left with only
           RA and DEC and query for Chandra observations at each position:

                % cut -c6- *.pos | vodata ivo://nasa.heasarc/chanmaster -p -

           Here  we used the unix 'cut' utility to remove the first column and
           pipe the resulting positions to the task, using the '-p  -'  option
           to indicate positions should be read from stding, and the IVO iden-
           tifier of the Chandra observation master  log  we  also  discovered
           from the Registry.

       10) Interactively  query for a count of Chandra observations of Messier

                % vodata -cq chandra -i -
                 chandra        335    I  Chandra X-Ray Observatory Data Archive
                   :             :         :            :       :

           Note that by using the '-i' flag we execute each query as  if  we'd
           put the object name on the command line.  Using the '-o' flag would
           instead read all of the objects from the stdin but then execute the
           queries in parallel following an EOF to terminate the input.

       11) Use  the  STILTS task 'tpipe' to select rows from a VOTable of QSOs
           (made with an earlier query) where the redshift is >  0.2.   Output
           only  the positions and pipe this to vodata to generate a new query
           to see whether HST has observed any of these objects:

                % stilts tpipe ifmt=votable qso_survey.vot
                    cmd='select "Z > 0.2"'
                       cmd='keepcols "RA DEC"' | vodata -p - hstpaec

           Note that we use the '-p -' flag to tell the task to take it's list
           of positions from the piped input.  The positions are used to query
           the HST Planned and Archived Exposure Catalog (hstpaec)

       12) The user has a task called 'wcsinfo' that takes a  list  of  images
           and  outputs  a  text table containing the plate center and size in
           degrees.  Use this task as part of a query for 2MASS point  sources
           contained in each image:

                % wcsinfo *.fits | vodata 2mass-psc -i -

           Here  we specify the desired service (2mass-psc) on the commandline
           as usual, and allow the remainder of the args  (i.e.  the  position
           and  search size) to be read from the stdin.  This allows for vari-
           able search sizes but processes the  positions  serially.   If  the
           sizes  are  all  the  same (say 25 arcmin), multiple queries can be
           done simultaneously using just a position file, e.g.

                % wcsinfo -pos_only *.fits > centers.txt
                % vodata -rm 25 2mass-psc centers.txt

       13) Query a large list of objects against a number of  ASCA  resources.
           Because  the  ASCA catalogs are served by the same machine, use the
           '-i' option and a  command  file  to  process  only  each  resource
           sequentially while still parallelizing the object lists:

                % cat cmds.txt
                ASCA  survey.tbl
                ASCA GIS  survey.tbl
                ASCA GPS  survey.tbl
                    :         :

                % vodata -i cmds.txt

       Note that we've needed to escape the space in the resource name in some
       cases.  To avoid this, use of the IVO identifier for each  resource  is
       usually preferred.

       14) Query the VO for GALEX data of M51.  Because the ShortName GALEX is
           not unique, we must either specify the IVO identifier of a specific
           service  to query,  or if we're interested in results from all sup-
           ported data services with galex in the name:

                % vodata -all galex M51

           The results come from the Cone and SIAP services both called GALEX,
           as  well  as an additional SIAP service called 'GALEX_Atlas'.  Note
           that the service names are case insensitive in either case.

       15) Process a list of hundreds of positions against the GSC2.2 catalog:

                % vodata gsc2.2 positions.txt

       16) Process a list of hundreds of positions against the GSC2.2 catalog,
           assume that the input table has a 5 line header of text  and  three
           columns  (id,ra,dec).   Note  that  the  cols  option  requires the
           optional id be specified last:

                % vodata --cols=2,3,1 --hskip=5 gsc2.2 positions.txt

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