Provided by: stilts_3.1.5-1_all bug

NAME

       stilts-cdsskymatch - Crossmatches table on sky position against VizieR/SIMBAD table

SYNOPSIS

       stilts cdsskymatch [ifmt=<in-format>] [istream=true|false] [in=<table>] [icmd=<cmds>]
                          [ocmd=<cmds>]
                          [omode=out|meta|stats|count|cgi|discard|topcat|samp|tosql|gui]
                          [out=<out-table>] [ofmt=<out-format>] [ra=<expr>] [dec=<expr>]
                          [radius=<value/arcsec>] [cdstable=<value>] [find=all|best|best-
                          remote|each|each-dist] [blocksize=<int-value>] [maxrec=<int-value>]
                          [compress=true|false] [serviceurl=<url-value>] [usemoc=true|false]
                          [presort=true|false] [fixcols=none|dups|all] [suffixin=<label>]
                          [suffixremote=<label>]

DESCRIPTION

       cdsskymatch uses the CDS X-Match service to join a local table to one of the tables hosted
       by the Centre de Données astronomiques de Strasbourg. This  includes  all  of  the  VizieR
       tables and the SIMBAD database. The service is very fast, and in most cases it is the best
       way to match a local table against a large external table  hosted  by  a  service.  It  is
       almost  certainly much better than using coneskymatch, though it is less flexible than TAP
       (see the tapquery task for flexible access to TAP services, and tapskymatch for positional
       matches).

       The  local  table  is  uploaded to the X-Match service in chunks, and the matches for each
       chunk are retrieved in turn and eventually stitched together to form the final result. The
       tool  only uploads sky position and an identifier for each row of the input table, but all
       columns of the input table are reinstated in the result for reference.

       The remote table in most cases contains only a subset of the the columns in  the  relevant
       VizieR  table,  including  the  most  useful  ones.  The  service  currently  provides  no
       straightforward way to acquire columns which are not returned by default.

       Acknowledgement: CDS note that if the use  of  the  X-Match  service  is  useful  to  your
       research,  they would appreciate the following acknowledgement: "This research made use of
       the cross-match service provided by CDS, Strasbourg."

OPTIONS

       ifmt=<in-format>
              Specifies the format of the input table as specified by  parameter  in.  The  known
              formats  are  listed in SUN/256. This flag can be used if you know what format your
              table is in. If it has the special value (auto) (the default), then an attempt will
              be made to detect the format of the table automatically. This cannot always be done
              correctly however, in which case the program will exit  with  an  error  explaining
              which formats were attempted.

       istream=true|false
              If  set  true,  the  input  table  specified  by the in parameter will be read as a
              stream. It is necessary to give the ifmt parameter in this case. Depending  on  the
              required operations and processing mode, this may cause the read to fail (sometimes
              it is necessary to read the table more than once). It is not normally necessary  to
              set this flag; in most cases the data will be streamed automatically if that is the
              best thing to do. However it can sometimes  result  in  less  resource  usage  when
              processing large files in certain formats (such as VOTable).

       in=<table>
              The location of the input table. This may take one of the following forms:

                * A filename.

                * A URL.

                * The  special  value  "-", meaning standard input. In this case the input format
                  must be given explicitly using the ifmt parameter. Note that  not  all  formats
                  can be streamed in this way.

                * A  system  command  line  with  either  a  "<" character at the start, or a "|"
                  character at the end ("<syscmd" or "syscmd|"). This executes the given pipeline
                  and  reads  from its standard output. This will probably only work on unix-like
                  systems.
               In any case, compressed data in one of the supported  compression  formats  (gzip,
              Unix compress or bzip2) will be decompressed transparently.

       icmd=<cmds>
              Specifies  processing  to be performed on the input table as specified by parameter
              in, before any other processing has taken place. The value of this parameter is one
              or  more  of  the  filter commands described in SUN/256. If more than one is given,
              they must be separated  by  semicolon  characters  (";").  This  parameter  can  be
              repeated  multiple  times on the same command line to build up a list of processing
              steps. The sequence of commands given in this way defines the  processing  pipeline
              which is performed on the table.

              Commands may alteratively be supplied in an external file, by using the indirection
              character '@'. Thus a value of "@filename" causes the file filename to be read  for
              a  list of filter commands to execute. The commands in the file may be separated by
              newline characters and/or semicolons, and lines which are blank or which start with
              a '#' character are ignored.

       ocmd=<cmds>
              Specifies  processing  to  be  performed  on  the  output  table,  after  all other
              processing has taken place. The value of this parameter  is  one  or  more  of  the
              filter  commands  described  in  SUN/256.  If  more than one is given, they must be
              separated by semicolon characters (";"). This parameter can  be  repeated  multiple
              times on the same command line to build up a list of processing steps. The sequence
              of commands given in this way defines the processing pipeline which is performed on
              the table.

              Commands may alteratively be supplied in an external file, by using the indirection
              character '@'. Thus a value of "@filename" causes the file filename to be read  for
              a  list of filter commands to execute. The commands in the file may be separated by
              newline characters and/or semicolons, and lines which are blank or which start with
              a '#' character are ignored.

       omode=out|meta|stats|count|cgi|discard|topcat|samp|tosql|gui
              The  mode  in which the result table will be output. The default mode is out, which
              means that the result will be written as a new  table  to  disk  or  elsewhere,  as
              determined  by the out and ofmt parameters. However, there are other possibilities,
              which correspond to uses to which a table can be put other than outputting it, such
              as  displaying  metadata,  calculating  statistics, or populating a table in an SQL
              database. For some values of this parameter,  additional  parameters  (<mode-args>)
              are required to determine the exact behaviour.

              Possible values are

                * out

                * meta

                * stats

                * count

                * cgi

                * discard

                * topcat

                * samp

                * tosql

                * gui
               Use the help=omode flag or see SUN/256 for more information.

       out=<out-table>
              The  location of the output table. This is usually a filename to write to. If it is
              equal to the special value "-" (the default) the output table will  be  written  to
              standard output.

              This parameter must only be given if omode has its default value of "out".

       ofmt=<out-format>
              Specifies  the format in which the output table will be written (one of the ones in
              SUN/256 - matching is case-insensitive and you can use just the first few letters).
              If  it  has the special value "(auto)" (the default), then the output filename will
              be examined to try to guess what sort of file is required usually by looking at the
              extension. If it's not obvious from the filename what output format is intended, an
              error will result.

              This parameter must only be given if omode has its default value of "out".

       ra=<expr>
              Right ascension in degrees in the ICRS coordinate system for the position  of  each
              row of the input table. This may simply be a column name, or it may be an algebraic
              expression calculated from columns as explained  in  SUN/256.  If  left  blank,  an
              attempt  is  made  to  guess  from  UCDs,  column  names  and unit annotations what
              expression to use.

       dec=<expr>
              Declination in degrees in the ICRS coordinate system for the position of  each  row
              of  the  input  table.  This may simply be a column name, or it may be an algebraic
              expression calculated from columns as explained  in  SUN/256.  If  left  blank,  an
              attempt  is  made  to  guess  from  UCDs,  column  names  and unit annotations what
              expression to use.

       radius=<value/arcsec>
              Maximum distance from the local table (ra,dec) position at which counterparts  from
              the remote table will be identified. This is a fixed value given in arcseconds, and
              must be in the range [0,180] (this limit is currently enforced by  the  CDS  Xmatch
              service).

       cdstable=<value>
              Identifier  of  the  table  from  the  CDS crossmatch service that is to be matched
              against the local table. This identifier may  be  the  standard  VizieR  identifier
              (e.g.  "II/246/out"  for  the 2MASS Point Source Catalogue) or "simbad" to indicate
              SIMBAD data.

              See for instance the TAPVizieR  table  searching  facility  at  http://tapvizier.u-
              strasbg.fr/adql/ to find VizieR catalogue identifiers.

       find=all|best|best-remote|each|each-dist
              Determines which pair matches are included in the result.

                * all: All matches

                * best: Matched rows, best remote row for each input row

                * best-remote: Matched rows, best input row for each remote row

                * each: One row per input row, contains best remote match or blank

                * each-dist: One row per input row, column giving distance only for best match
               Note only the all mode is symmetric between the two tables.

              Note  also  that  there  is  a bug in best-remote matching. If the match is done in
              multiple blocks, it's possible for a remote table row to appear matched against one
              local  table row per uploaded block, rather than just once for the whole result. If
              you're worried about that, set blocksize >= rowCount. This may be fixed in a future
              release.

       blocksize=<int-value>
              The  CDS  Xmatch  service operates limits on the maximum number of rows that can be
              uploaded and the maximum number of rows that is returned as a result from a  single
              query. In the case of large input tables, they are broken down into smaller blocks,
              and one request is sent to the external service  for  each  block.  This  parameter
              controls  the number of rows in each block. For an input table with fewer rows than
              this value, the whole thing is done as a single request.

              At time of writing, the maximum upload size is 100Mb (about 3Mrow;  this  does  not
              depend on the width of your table), and the maximum return size is 2Mrow.

              Large  blocksizes  tend to be good (up to a point) for reducing the total amount of
              time a large xmatch operation takes, but they can make it harder  to  see  the  job
              progressing.  There  is  also the danger (for ALL-type find modes) of exceeding the
              return size limit, which will result in truncation of the returned result.

       maxrec=<int-value>
              Limit to the number of rows resulting from this operation. If the value is negative
              (the default) no limit is imposed. Note however that there can be truncation of the
              result if the number of records returned from a single chunk  exceeds  the  service
              hard limit (2,000,000 at time of writing).

       compress=true|false
              If  true,  the  service  is  requested  to  provide  HTTP-level compression for the
              response stream (Accept-Encoding header is set to "gzip", see RFC 2616). This  does
              not  guarantee that compression will happen but if the service honours this request
              it may result in a smaller amount  of  network  traffic  at  the  expense  of  more
              processing on the server and client.

       serviceurl=<url-value>
              The  URL  at which the CDS Xmatch service can be found. Normally this should not be
              altered from the default, but if other implementations  of  the  same  service  are
              known, this parameter can be used to access them.

       usemoc=true|false
              If true, first acquire a MOC coverage map from CDS, and use that to pre-filter rows
              before uploading them for matching. This should improve  efficiency,  but  have  no
              effect on the result.

       presort=true|false
              If  true,  the rows are sorted by HEALPix index before they are uploaded to the CDS
              X-Match service. If the  match  is  done  in  multiple  blocks,  this  may  improve
              efficiency,  since  when  matching  against  a  large  remote catalogue the X-Match
              service likes to process requests in which sources are grouped into a small  region
              rather than scattered all over the sky.

              Note this will have a couple of other side effects that may be undesirable: it will
              read all the input rows into the task at once, which may make it harder  to  assess
              progress, and it will affect the order of the rows in the output table.

              It is probably only worth setting true for rather large (multi-million-row?) multi-
              block matches, where both local and remote catalogues are spread over a significant
              fraction of the sky. But feel free to experiment.

       fixcols=none|dups|all
              Determines  how  input  columns  are  renamed  before  use in the output table. The
              choices are:

                * none: columns are not renamed

                * dups: columns which would otherwise have duplicate names in the output will  be
                  renamed to indicate which table they came from

                * all: all columns will be renamed to indicate which table they came from
               If columns are renamed, the new ones are determined by suffix* parameters.

       suffixin=<label>
              If  the  fixcols  parameter  is set so that input columns are renamed for insertion
              into the output table, this parameter determines how the renaming is done. It gives
              a suffix which is appended to all renamed columns from the input table.

       suffixremote=<label>
              If  the  fixcols  parameter  is set so that input columns are renamed for insertion
              into the output table, this parameter determines how the renaming is done. It gives
              a suffix which is appended to all renamed columns from the CDS result table.

SEE ALSO

       stilts(1)

       If  the  package  stilts-doc  is installed, the full documentation SUN/256 is available in
       HTML format:
       file:///usr/share/doc/stilts-doc/sun256/index.html

VERSION

       STILTS version 3.1-5-debian

       This is the Debian version of Stilts, which lack the support  of  some  file  formats  and
       network protocols. For differences see
       file:///usr/share/doc/stilts/README.Debian

AUTHOR

       Mark Taylor (Bristol University)

                                             Mar 2017                       STILTS-CDSSKYMATCH(1)