CDS MOC Service (astroquery.cds)

Getting started

This module provides a python interface for querying the CDS MOCServer.

MOC is an IVOA standard enabling description of arbitrary sky regions. Based on the HEALPix sky tessellation, it maps regions on the sky into hierarchically grouped predefined cells. It corresponds to a set of HEALPix cells at different orders.

For those wanting to know more about MOCs, please refer to this IVOA paper and the MOCPy’s documentation developed by the CDS.

CDS has set up a server known as the MOCServer storing data-set names each associated with a MOC spatial coverage and some meta-datas giving a more detailed explanation of the data-set.

The MOCServer aims at returning the data-sets having at least one source lying in a specific sky region defined by the user. Internally the MOCServer performs the intersection between the given sky region and the MOCs associated with each data-sets. Because the MOC associated to a data-set describes its sky coverage, if the above intersection is not null then the MOCServer knows that some sources of this data-set are in the user defined sky region.

To be aware of what the MOCServer returns, please refers to this link. We have queried the MOCServer with a cone region of center ra, dec = (10.8, 32.2) deg and radius = 1.5 deg. In return, the MOCServer gives a list of data-sets each tagged with an unique ID along with some other meta-datas too e.g. obs_title, obs_description, moc_access_url (url for accessing the MOC associated with the data-set. Usually a FITS file storing a list of HEALPix cells).

It is also possible to ask the MOCServer for retrieving data-sets based on their meta-data values. Here we have queried the MOCServer for only the image data-sets being in the cone defined above (dataproduct_type meta-data equals to "image").

This package implements two methods:

  • query_region() retrieving data-sets (their associated MOCs and meta-datas) having sources in a given region.
  • find_datasets() retrieving data-sets (their associated MOCs and meta-datas) based on the values of their meta-datas.

Requirements

The following packages are required for the use of this module:

Examples

Performing a CDS MOC query on a cone region

The first thing to do is to import the regions package and the cds module.

>>> from astropy import coordinates
>>> from regions import CircleSkyRegion
>>> from astroquery.cds import cds

cds implements the method query_region() and this is what we will use. First, we need to define a cone region. For that purpose we will instantiate a regions.CircleSkyRegion object:

>>> center = coordinates.SkyCoord(10.8, 32.2, unit='deg')
>>> radius = coordinates.Angle(1.5, unit='deg')

>>> cone = CircleSkyRegion(center, radius)

And basically call the query_region() method with the cone and that’s all.

>>> cds.query_region(region=cone)
<Table masked=True length=1317>
hips_service_url_8        hips_status         hips_status_7 ...   hipsgen_date_5                                  hips_master_url                                  moc_sky_fraction
      object                 object               object    ...       object                                           object                                          float64
------------------ -------------------------- ------------- ... ----------------- -------------------------------------------------------------------------------- ----------------
                --                         --            -- ...                --                                                                               --           0.0588
                --                         --            -- ...                --                                                                               --        2.066e-06
                --                         --            -- ...                --                                                                               --         0.002134
                --                         --            -- ...                --                                                                               --         0.003107
                --                         --            -- ...                --                                                                               --        0.0001764
                --                         --            -- ...                --                                                                               --         0.008365
                --                         --            -- ...                --                                                                               --        0.0009891
                --                         --            -- ...                --                                                                               --        0.0004252
                --                         --            -- ...                --                                                                               --        0.0006163
                --                         --            -- ...                --                                                                               --        0.0008544
                --                         --            -- ...                --                                                                               --        0.0009243
                --                         --            -- ...                --                                                                               --          0.00016
                --                         --            -- ...                --                                                                               --         0.000729
                --                         --            -- ...                --                                                                               --        2.998e-05
                --                         --            -- ...                --                                                                               --          0.01136
                --                         --            -- ...                --                                                                               --        0.0006112
                --                         --            -- ...                --                                                                               --        6.632e-05
                --                         --            -- ...                --                                                                               --        0.0001141
                --                         --            -- ...                --                                                                               --        0.0008666
                --                         --            -- ...                --                                                                               --         0.001025
                --                         --            -- ...                --                                                                               --         0.008088
                --                         --            -- ...                --                                                                               --         0.000282
                --                         --            -- ...                --                                                                               --         0.002413
                --                         --            -- ...                --                                                                               --        0.0001468
                -- public master clonableOnce            -- ...                --                                                                               --           0.3164
                -- public master clonableOnce            -- ...                --                                                                               --              1.0
                --                         --            -- ...                --                                                                               --        4.444e-05
                --                         --            -- ...                --                                                                               --        4.641e-05
                --                         --            -- ...                --                                                                               --          0.00044
               ...                        ...           ... ...               ...                                                                              ...              ...
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --    http://cade.irap.omp.eu/documents/Ancillary/4Aladin/DRAO-VillaElisa_21cm_POLQ              1.0
                --   public master unclonable            -- ...                --    http://cade.irap.omp.eu/documents/Ancillary/4Aladin/DRAO-VillaElisa_21cm_POLU              1.0
                --   public master unclonable            -- ...                --                   http://cade.irap.omp.eu/documents/Ancillary/4Aladin/DRAO_22MHz           0.7283
                --   public master unclonable            -- ... 2017-02-09T13:48Z                                                                               --           0.5723
                --   public master unclonable            -- ...                --                                                                               --           0.5468
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                http://cade.irap.omp.eu/documents/Ancillary/4Aladin/GAURIBIDANUR/           0.8623
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --           0.9635
                --   public master unclonable            -- ...                --                                                                               --           0.4284
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                --                                                                               --              1.0
                --   public master unclonable            -- ...                -- http://cade.irap.omp.eu/documents/Ancillary/4Aladin/STOCKERT+VILLAELISA_1420MHz/              1.0
                --   public master unclonable            -- ...                --                                                                               --            0.181
                --   public master unclonable            -- ...                --                                                                               --           0.1918
                --   public master unclonable            -- ... 2017-05-15T12:44Z                                                                               --              1.0
                --                         --            -- ...                --                                                                               --           0.1553
                --                         --            -- ...                --                                                                               --           0.2373
                -- public master clonableOnce            -- ...                --                                                                               --          0.08287
                -- public master clonableOnce            -- ...                --                                                                               --          0.02227
                -- public master clonableOnce            -- ...                --                                                                               --          0.02227
                -- public master clonableOnce            -- ...                --                                                                               --          0.02227

You can also query the MOCServer on a regions.PolygonSkyRegion or even an mocpy.MOC following the same pattern i.e. just by replacing cone with a polygon or a MOC object.

By default, query_region() returns an astropy.table.Table object storing the data-sets as rows and their meta-datas as columns. Data-sets might have no information for a specific meta-data. If so, the value associated with this meta-data for this data-set is set to “-“. The above astropy table looks like :

Retrieve only a subset of meta-datas

This table refers to a lot of meta-datas whereas we could only use a few of them. In fact, it is possible to ask the MOCServer to give us a reduced set of meta-datas for the resulting data-sets. The table returned by the MOCServer will be lighter and thus faster to retrieve.

The parameter fields of query_region() allows us to provide the list of meta-datas we want to get. Let’s say we would like only the ID, the moc_sky_fraction and the moc_access_url of the resulting data-sets:

>>> cds.query_region(region=cone, fields=['ID', 'moc_sky_fraction', 'moc_access_url'])
<Table masked=True length=1317>
                                   moc_access_url                                                     ID                  moc_sky_fraction
                                       object                                                       str48                     float64
------------------------------------------------------------------------------------ ------------------------------------ ----------------
http://alasky.unistra.fr/footprints/tables/vizier/B_assocdata_obscore/MOC?nside=2048              CDS/B/assocdata/obscore           0.0588
      http://alasky.unistra.fr/footprints/tables/vizier/B_cb_lmxbdata/MOC?nside=2048                    CDS/B/cb/lmxbdata        2.066e-06
        http://alasky.unistra.fr/footprints/tables/vizier/B_cfht_cfht/MOC?nside=2048                      CDS/B/cfht/cfht         0.002134
     http://alasky.unistra.fr/footprints/tables/vizier/B_cfht_obscore/MOC?nside=2048                   CDS/B/cfht/obscore         0.003107
  http://alasky.unistra.fr/footprints/tables/vizier/B_chandra_chandra/MOC?nside=2048                CDS/B/chandra/chandra        0.0001764
      http://alasky.unistra.fr/footprints/tables/vizier/B_eso_eso_arc/MOC?nside=2048                    CDS/B/eso/eso_arc         0.008365
    http://alasky.unistra.fr/footprints/tables/vizier/B_gcvs_gcvs_cat/MOC?nside=2048                  CDS/B/gcvs/gcvs_cat        0.0009891
     http://alasky.unistra.fr/footprints/tables/vizier/B_gcvs_nsv_cat/MOC?nside=2048                   CDS/B/gcvs/nsv_cat        0.0004252
   http://alasky.unistra.fr/footprints/tables/vizier/B_gemini_obscore/MOC?nside=2048                 CDS/B/gemini/obscore        0.0006163
       http://alasky.unistra.fr/footprints/tables/vizier/B_hst_hstlog/MOC?nside=2048                     CDS/B/hst/hstlog        0.0008544
      http://alasky.unistra.fr/footprints/tables/vizier/B_hst_obscore/MOC?nside=2048                    CDS/B/hst/obscore        0.0009243
        http://alasky.unistra.fr/footprints/tables/vizier/B_hst_wfpc2/MOC?nside=2048                      CDS/B/hst/wfpc2          0.00016
     http://alasky.unistra.fr/footprints/tables/vizier/B_jcmt_obscore/MOC?nside=2048                   CDS/B/jcmt/obscore         0.000729
    http://alasky.unistra.fr/footprints/tables/vizier/B_merlin_merlin/MOC?nside=2048                  CDS/B/merlin/merlin        2.998e-05
       http://alasky.unistra.fr/footprints/tables/vizier/B_mk_mktypes/MOC?nside=2048                     CDS/B/mk/mktypes          0.01136
    http://alasky.unistra.fr/footprints/tables/vizier/B_pastel_pastel/MOC?nside=2048                  CDS/B/pastel/pastel        0.0006112
         http://alasky.unistra.fr/footprints/tables/vizier/B_sb9_main/MOC?nside=2048                       CDS/B/sb9/main        6.632e-05
         http://alasky.unistra.fr/footprints/tables/vizier/B_sn_sncat/MOC?nside=2048                       CDS/B/sn/sncat        0.0001141
   http://alasky.unistra.fr/footprints/tables/vizier/B_subaru_suprimc/MOC?nside=2048                 CDS/B/subaru/suprimc        0.0008666
   http://alasky.unistra.fr/footprints/tables/vizier/B_swift_swiftlog/MOC?nside=2048                 CDS/B/swift/swiftlog         0.001025
          http://alasky.unistra.fr/footprints/tables/vizier/B_vsx_vsx/MOC?nside=2048                        CDS/B/vsx/vsx         0.008088
       http://alasky.unistra.fr/footprints/tables/vizier/B_wd_catalog/MOC?nside=2048                     CDS/B/wd/catalog         0.000282
          http://alasky.unistra.fr/footprints/tables/vizier/B_wds_wds/MOC?nside=2048                        CDS/B/wds/wds         0.002413
       http://alasky.unistra.fr/footprints/tables/vizier/B_xmm_xmmlog/MOC?nside=2048                     CDS/B/xmm/xmmlog        0.0001468
                                                                                  --                 CDS/C/GALFAHI/Narrow           0.3164
                                                                                  --                       CDS/C/HI4PI/HI              1.0
         http://alasky.unistra.fr/footprints/tables/vizier/I_100A_w10/MOC?nside=2048                       CDS/I/100A/w10        4.444e-05
         http://alasky.unistra.fr/footprints/tables/vizier/I_100A_w25/MOC?nside=2048                       CDS/I/100A/w25        4.641e-05
         http://alasky.unistra.fr/footprints/tables/vizier/I_100A_w50/MOC?nside=2048                       CDS/I/100A/w50          0.00044
                                                                                 ...                                  ...              ...
                                                                                  --                 ov-gso/P/DIRBE/ZSMA9              1.0
                                                                                  --   ov-gso/P/DRAO-VillaElisa/21cm/POLQ              1.0
                                                                                  --   ov-gso/P/DRAO-VillaElisa/21cm/POLU              1.0
                                                                                  --                  ov-gso/P/DRAO/22MHz           0.7283
                                                                                  --            ov-gso/P/DWINGELOO/820MHz           0.5723
                                                                                  --                       ov-gso/P/EBHIS           0.5468
                                                                                  --                  ov-gso/P/GASS+EBHIS              1.0
                                                                                  --                ov-gso/P/GAURIBIDANUR           0.8623
                                                                                  --                      ov-gso/P/IRIS/1              1.0
                                                                                  --                      ov-gso/P/IRIS/2              1.0
                                                                                  --                      ov-gso/P/IRIS/3              1.0
                                                                                  --                      ov-gso/P/IRIS/4              1.0
                                                                                  --                         ov-gso/P/LAB              1.0
                                                                                  --                    ov-gso/P/MAIPU-MU           0.9635
                                                                                  --                      ov-gso/P/MITEoR           0.4284
                                                                                  --                        ov-gso/P/RASS              1.0
                                                                                  --                    ov-gso/P/RASS/EXP              1.0
                                                                                  --               ov-gso/P/RASS/HardBand              1.0
                                                                                  --               ov-gso/P/RASS/SoftBand              1.0
                                                                                  -- ov-gso/P/STOCKERT+VILLAELISA/1420MHz              1.0
                                                                                  --                   ov-gso/P/VTSS/CONT            0.181
                                                                                  --                     ov-gso/P/VTSS/Ha           0.1918
                                                                                  --                        ov-gso/P/WHAM              1.0
                                                                                  --                   svo.cab/cat/catlib           0.1553
                                                                                  --                    svo.cab/cat/miles           0.2373
                                                                                  --                xcatdb/P/XMM/PN/color          0.08287
                                                                                  --                  xcatdb/P/XMM/PN/eb2          0.02227
                                                                                  --                  xcatdb/P/XMM/PN/eb3          0.02227
                                                                                  --                  xcatdb/P/XMM/PN/eb4          0.02227

This astropy table now have only 3 columns and can be manipulated much faster.

Retrieving data-sets based on their meta-data values

As expressed in the last paragraph of the Getting Started section, we can ask the MOCServer to do some filtering tasks for us at the server side. The meta_data parameter of query_region() allows the user to write an algebraic expression on the meta-datas. Let’s query the MOCServer for retrieving what we have done using the web interface in the Getting Started section i.e. retrieving only the image data-sets that lie in the previously defined cone.

>>> cds.query_region(region=cone,
...                  fields=['ID', 'dataproduct_type', 'moc_sky_fraction', 'moc_access_url'],
...                  meta_data="dataproduct_type=image")
<Table masked=True length=279>
                             moc_access_url                                                 ID                   dataproduct_type moc_sky_fraction
                                 object                                                   str48                        str5           float64
------------------------------------------------------------------------ --------------------------------------- ---------------- ----------------
                             http://alasky.u-strasbg.fr/2MASS/H/Moc.fits                           CDS/P/2MASS/H            image              1.0
                             http://alasky.u-strasbg.fr/2MASS/J/Moc.fits                           CDS/P/2MASS/J            image              1.0
                             http://alasky.u-strasbg.fr/2MASS/K/Moc.fits                           CDS/P/2MASS/K            image              1.0
                         http://alasky.u-strasbg.fr/2MASS/Color/Moc.fits                       CDS/P/2MASS/color            image              1.0
                http://alasky.u-strasbg.fr/AKARI-FIS/ColorLSN60/Moc.fits                   CDS/P/AKARI/FIS/Color            image              1.0
                      http://alasky.u-strasbg.fr/AKARI-FIS/N160/Moc.fits                    CDS/P/AKARI/FIS/N160            image           0.9988
                       http://alasky.u-strasbg.fr/AKARI-FIS/N60/Moc.fits                     CDS/P/AKARI/FIS/N60            image           0.9976
                     http://alasky.u-strasbg.fr/AKARI-FIS/WideL/Moc.fits                   CDS/P/AKARI/FIS/WideL            image           0.9989
                     http://alasky.u-strasbg.fr/AKARI-FIS/WideS/Moc.fits                   CDS/P/AKARI/FIS/WideS            image           0.9976
                                                                      --                     CDS/P/Ariel/Voyager            image              1.0
                                  http://alasky.u-strasbg.fr/CO/Moc.fits                                CDS/P/CO            image              1.0
                                                                      -- CDS/P/Callisto/Voyager-Galileo-simp-1km            image              1.0
                                                                      --        CDS/P/Charon/NewHorizon-PIA19866            image              1.0
                                                                      --            CDS/P/DM/flux-Bp/I/345/gaia2            image              1.0
                                                                      --             CDS/P/DM/flux-G/I/345/gaia2            image              1.0
                                                                      --            CDS/P/DM/flux-Rp/I/345/gaia2            image              1.0
                                                                      -- CDS/P/DM/flux-color-Rp-G-Bp/I/345/gaia2            image              1.0
                                                                      --                          CDS/P/DSS2/NIR            image           0.9943
                  http://alasky.u-strasbg.fr/DSS/DSS2-blue-XJ-S/Moc.fits                         CDS/P/DSS2/blue            image           0.9956
                        http://alasky.u-strasbg.fr/DSS/DSSColor/Moc.fits                        CDS/P/DSS2/color            image              1.0
                      http://alasky.u-strasbg.fr/DSS/DSS2Merged/Moc.fits                          CDS/P/DSS2/red            image              1.0
                                                                      --            CDS/P/Dione/Cassini-PIA12577            image              1.0
   http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_100-150/Moc.fits                 CDS/P/EGRET/Dif/100-150            image              1.0
 http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_1000-2000/Moc.fits               CDS/P/EGRET/Dif/1000-2000            image              1.0
   http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_150-300/Moc.fits                 CDS/P/EGRET/Dif/150-300            image              1.0
 http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_2000-4000/Moc.fits               CDS/P/EGRET/Dif/2000-4000            image              1.0
     http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_30-50/Moc.fits                   CDS/P/EGRET/Dif/30-50            image              1.0
   http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_300-500/Moc.fits                 CDS/P/EGRET/Dif/300-500            image              1.0
http://alasky.u-strasbg.fr/EGRET/EGRET-dif/EGRET_dif_4000-10000/Moc.fits              CDS/P/EGRET/Dif/4000-10000            image              1.0
                                                                     ...                                     ...              ...              ...
                                                                      --                    ov-gso/P/DIRBE/ZSMA7            image              1.0
                                                                      --                    ov-gso/P/DIRBE/ZSMA8            image              1.0
                                                                      --                    ov-gso/P/DIRBE/ZSMA9            image              1.0
                                                                      --      ov-gso/P/DRAO-VillaElisa/21cm/POLQ            image              1.0
                                                                      --      ov-gso/P/DRAO-VillaElisa/21cm/POLU            image              1.0
                                                                      --                     ov-gso/P/DRAO/22MHz            image           0.7283
                                                                      --               ov-gso/P/DWINGELOO/820MHz            image           0.5723
                                                                      --                          ov-gso/P/EBHIS            image           0.5468
                                                                      --                     ov-gso/P/GASS+EBHIS            image              1.0
                                                                      --                   ov-gso/P/GAURIBIDANUR            image           0.8623
                                                                      --                         ov-gso/P/IRIS/1            image              1.0
                                                                      --                         ov-gso/P/IRIS/2            image              1.0
                                                                      --                         ov-gso/P/IRIS/3            image              1.0
                                                                      --                         ov-gso/P/IRIS/4            image              1.0
                                                                      --                            ov-gso/P/LAB            image              1.0
                                                                      --                       ov-gso/P/MAIPU-MU            image           0.9635
                                                                      --                         ov-gso/P/MITEoR            image           0.4284
                                                                      --                           ov-gso/P/RASS            image              1.0
                                                                      --                       ov-gso/P/RASS/EXP            image              1.0
                                                                      --                  ov-gso/P/RASS/HardBand            image              1.0
                                                                      --                  ov-gso/P/RASS/SoftBand            image              1.0
                                                                      --    ov-gso/P/STOCKERT+VILLAELISA/1420MHz            image              1.0
                                                                      --                      ov-gso/P/VTSS/CONT            image            0.181
                                                                      --                        ov-gso/P/VTSS/Ha            image           0.1918
                                                                      --                           ov-gso/P/WHAM            image              1.0
                                                                      --                   xcatdb/P/XMM/PN/color            image          0.08287
                                                                      --                     xcatdb/P/XMM/PN/eb2            image          0.02227
                                                                      --                     xcatdb/P/XMM/PN/eb3            image          0.02227
                                                                      --                     xcatdb/P/XMM/PN/eb4            image          0.02227

Looking at the dataproduct_type column, all the data-sets seem to be images. We could have been done that using numpy operations on astropy.table.Table objects but here the MOCServer made it for us.

This page on the web interface of the MOCServer gives examples of some filtering expressions.

Alternatively, the method find_datasets() searches data-sets on the whole sky. If you want to get the MOCs or meta-datas from some specific data-sets this is the method to use. The next example retrieves all the moc_access_url of the Hubble surveys:

>>> cds.find_datasets(meta_data="ID=*HST*",
...                   fields=['ID', 'moc_access_url'])
<Table masked=True length=42>
                   moc_access_url                             ID
                       object                               str21
--------------------------------------------------- ---------------------
                                                 --           CDS/P/HST/B
                                                 --          CDS/P/HST/CO
     http://alasky.unistra.fr/GOODS/GOODSb/Moc.fits     CDS/P/HST/GOODS/b
http://alasky.unistra.fr/GOODS/GOODS-color/Moc.fits CDS/P/HST/GOODS/color
     http://alasky.unistra.fr/GOODS/GOODSi/Moc.fits     CDS/P/HST/GOODS/i
     http://alasky.unistra.fr/GOODS/GOODSv/Moc.fits     CDS/P/HST/GOODS/v
     http://alasky.unistra.fr/GOODS/GOODSz/Moc.fits     CDS/P/HST/GOODS/z
                                                 --           CDS/P/HST/H
                                                 --         CDS/P/HST/H2O
                                                 --      CDS/P/HST/Halpha
                                                 --       CDS/P/HST/Hbeta
                                                 --           CDS/P/HST/I
                                                 --           CDS/P/HST/J
                                                 --         CDS/P/HST/NII
                                                 --         CDS/P/HST/OII
                                                 --        CDS/P/HST/OIII
     http://alasky.u-strasbg.fr/PHAT/F110W/Moc.fits  CDS/P/HST/PHAT/F110W
     http://alasky.u-strasbg.fr/PHAT/F160W/Moc.fits  CDS/P/HST/PHAT/F160W
     http://alasky.u-strasbg.fr/PHAT/F275W/Moc.fits  CDS/P/HST/PHAT/F275W
     http://alasky.u-strasbg.fr/PHAT/F336W/Moc.fits  CDS/P/HST/PHAT/F336W
     http://alasky.u-strasbg.fr/PHAT/F475W/Moc.fits  CDS/P/HST/PHAT/F475W
     http://alasky.u-strasbg.fr/PHAT/F814W/Moc.fits  CDS/P/HST/PHAT/F814W
                                                 --      CDS/P/HST/Palpha
                                                 --    CDS/P/HST/Palpha_c
                                                 --           CDS/P/HST/R
                                                 --       CDS/P/HST/SDSSg
                                                 --       CDS/P/HST/SDSSr
                                                 --       CDS/P/HST/SDSSz
                                                 --        CDS/P/HST/SIII
                                                 --           CDS/P/HST/U
                                                 --          CDS/P/HST/UV
                                                 --           CDS/P/HST/V
                                                 --           CDS/P/HST/Y
                                                 --       CDS/P/HST/other
                                                 --      CDS/P/HST/wideUV
                                                 --       CDS/P/HST/wideV
                                                 --  ESAVO/P/HST/ACS-blue
                                                 --       ESAVO/P/HST/FOC
                                                 --    ESAVO/P/HST/NICMOS
                                                 --      ESAVO/P/HST/WFC3
                                                 --      ESAVO/P/HST/WFPC
                                                 --     ESAVO/P/HST/WFPC2

Misc

Limiting the number of returned data-sets

Another parameter called max_rec specifies an upper limit for the number of data-sets to be returned:

>>> cds.query_region(region=cone, max_rec=3)
<Table masked=True length=3>
publisher_id                 obs_description_url                                                     moc_access_url                                    ...    TIMESTAMP    obs_label moc_sky_fraction
    str9                            str52                                                                str84                                         ...     float64        str8       float64
------------ ---------------------------------------------------- ------------------------------------------------------------------------------------ ... --------------- --------- ----------------
   ivo://CDS http://cdsarc.u-strasbg.fr/viz-bin/Cat?B%2Fassocdata http://alasky.unistra.fr/footprints/tables/vizier/B_assocdata_obscore/MOC?nside=2048 ... 1531742659000.0   obscore           0.0588
   ivo://CDS        http://cdsarc.u-strasbg.fr/viz-bin/Cat?B%2Fcb       http://alasky.unistra.fr/footprints/tables/vizier/B_cb_lmxbdata/MOC?nside=2048 ... 1531742660000.0  lmxbdata        2.066e-06
   ivo://CDS      http://cdsarc.u-strasbg.fr/viz-bin/Cat?B%2Fcfht         http://alasky.unistra.fr/footprints/tables/vizier/B_cfht_cfht/MOC?nside=2048 ... 1531742660000.0      cfht         0.002134

This astropy table has only 3 rows although we know more data-sets match the query. It’s useful if you do not need to retrieve all the data-sets matching a query but only a few. Again, the result will come faster from the MOCServer because this operation is done at the server side.

Returning a MOC object as a result

Some users might want the union of all the MOCs from the data-sets matching the query. You can get a mocpy.MOC object instead of an astropy.table.Table by setting the parameter return_moc to True. An additional parameter max_norder allows the user to set the resolution/precision of the returned MOC that he wants.

As an example, we would like to obtain the union of the spatial coverage of all the Hubble surveys:

>>> from mocpy import MOC
>>> # We want to retrieve all the HST surveys i.e. the HST surveys covering any region of the sky.
>>> allsky = CircleSkyRegion(coordinates.SkyCoord(0, 0, unit="deg"), coordinates.Angle(180, unit="deg"))
>>> moc = cds.query_region(region=allsky,
... # We want a mocpy object instead of an astropy table
...                        return_moc=True,
... # The order of the MOC
...                         max_norder=7,
... # Expression on the ID meta-data
...                        meta_data="ID=*HST*")
>>> moc.plot(title="Union of the spatial coverage of all the Hubble surveys.")
../_images/HST_union.png

Retrieve the MOC of a specific data-set

Finally, if you want to retrieve the MOC of a specific data-set, please consider using the find_datasets method with the ID of the data-set you want to retrieve the MOC along with the return_moc parameter set to True. The last example will show you how to get the MOC (i.e. a mocpy.MOC object) of the GALEXGR6/AIS/FUV survey.

>>> from mocpy import MOC
>>> moc_galex=cds.find_datasets(meta_data="ID=CDS/P/GALEXGR6/AIS/FUV", return_moc=True)
>>> moc_galex.plot("MOC associated to CDS/P/GALEXGR6/AIS/FUV.")
../_images/MOC_GALEXGR6_AIS_FUV.png

The cds package can therefore be used in complementarity with mocpy. We can now retrieve mocpy.MOC objects coming from the MOCServer and manipulate them in a python session with mocpy.

Reference/API

astroquery.cds Package

CDS MOCServer Query Tool

Author:Matthieu Baumann (matthieu.baumann@astro.unistra.fr)

This package is for querying the CDS MOC service, primarily hosted at:

Note: If the access to MOCs with the MOCServer tool was helpful for your research work, the following acknowledgment would be appreciated:

This research has made use of the MOCServer, a tool developed at CDS, Strasbourg, France aiming at retrieving
MOCs/meta-data from known data-sets. MOC is an IVOA standard described in the following paper :
http://www.ivoa.net/documents/MOC/20140602/REC-MOC-1.0-20140602.pdf

Classes

CdsClass() Query the CDS MOCServer
Conf Configuration parameters for astroquery.template_module.