Provided by: stilts_3.4.3-1_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|checksum|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.

       For a better understanding of the details of how this service operates, including  exactly
       what  coordinates are matched against the uploaded positions (roughly: integrated to J2000
       using proper motions if available) and what columns are included in the output (roughly: a
       subset of the most commonly used columns), please consult the service documentation.

       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.  This  parameter  is  ignored  for  scheme-specified
              tables.

       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). This parameter is
              ignored for scheme-specified tables.

       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 scheme specification of the form :<scheme-name>:<scheme-args>.

                * 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|checksum|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

                * checksum

                * 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/sun256/index.html

VERSION

       STILTS version 3.4.3-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)