Provided by: stilts_3.1.5-1_all bug

NAME

       stilts-tskymatch2 - Crossmatches 2 tables on sky position

SYNOPSIS

       stilts tskymatch2 [in1=<table1>] [ifmt1=<in-format>] [in2=<table2>] [ifmt2=<in-format>]
                         [omode=out|meta|stats|count|cgi|discard|topcat|samp|tosql|gui]
                         [out=<out-table>] [ofmt=<out-format>] [ra1=<expr>] [dec1=<expr>]
                         [ra2=<expr>] [dec2=<expr>] [error=<value/arcsec>] [tuning=<healpix-k>]
                         [join=1and2|1or2|all1|all2|1not2|2not1|1xor2]
                         [find=all|best|best1|best2]

DESCRIPTION

       tskymatch2 performs a crossmatch of two tables based on the proximity  of  sky  positions.
       You  specify  the columns or expressions giving right ascension and declination in degrees
       for each input table,  and  a  maximum  permissible  separation  in  arcseconds,  and  the
       resulting joined table is output.

       If  you omit expressions for the RA and Dec, an attempt is made to identify the columns to
       use using column Unified Content  Descriptors  (UCDs)  or  names.  First  columns  bearing
       appropriate    UCD1   or   UCD1+   values   (POS_EQ_RA,   POS_EQ_RA_MAIN,   pos.eq.ra   or
       pos.eq.ra;meta.main and their equivalents for declination) are sought. If these cannot  be
       found,  columns  named something like "RA" or "RA2000" are sought. If either is found, the
       column units are consulted and  radian->degree  conversions  are  performed  if  necessary
       (degrees  are assumed if no unit value is given). If nothing likely can be found, then the
       command will fail with an error message. This search logic is intended  as  a  convenience
       only;  it  is  somewhat  ad hoc and subject to change. To make sure that the correct angle
       values are being used, specify the ra and dec position parameters explicitly.

       tskymatch2 is simply a cut-down version, provided for convenience,  of  the  more  general
       matching  task  tmatch2. If you want more match options or otherwise more configurability,
       you can probably find it by using tmatch2.

OPTIONS

       in1=<table1>
              The location of the first 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 ifmt1 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.

       ifmt1=<in-format>
              Specifies the format of the first input table as specified by  parameter  in1.  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.

       in2=<table2>
              The location of the second 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 ifmt2 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.

       ifmt2=<in-format>
              Specifies  the  format of the second input table as specified by parameter in2. 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.

       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".

       ra1=<expr>
              Right ascension in degrees for the position of each row of table 1. 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.

       dec1=<expr>
              Declination in degrees for the position of each row of table 1. 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.

       ra2=<expr>
              Right ascension in degrees for the position of each row of table 2. 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.

       dec2=<expr>
              Declination in degrees for the position of each row of table 2. 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.

       error=<value/arcsec>
              The  maximum separation permitted between two objects for them to count as a match.
              Units are arc seconds.

       tuning=<healpix-k>
              Tuning parameter that controls the pixel size used when binning the rows. The legal
              range  is from 0 (corresponding to pixel size of about 60 degrees) to 20 (about 0.2
              arcsec). The value of this parameter will not affect the result but may affect  the
              performance  in terms of CPU and memory resources required. A default value will be
              chosen based on the size of the error parameter, but it may be possible to  improve
              performance by adjusting the default value. The value used can be seen by examining
              the progress output. If your match is taking a long time or is failing from lack of
              memory it may be worth trying different values for this parameter.

       join=1and2|1or2|all1|all2|1not2|2not1|1xor2
              Determines  which  rows  are  included  in the output table. The matching algorithm
              determines which of the rows from the first table correspond to which rows from the
              second.  This  parameter  determines  what to do with that information. Perhaps the
              most obvious thing is to write out a table containing only rows which correspond to
              a  row  in  both  of  the  two  input tables. However, you may also want to see the
              unmatched rows from one or both input tables, or rows  present  in  one  table  but
              unmatched in the other, or other possibilities. The options are:

                * 1and2: An output row for each row represented in both input tables (INNER JOIN)

                * 1or2:  An  output  row  for each row represented in either or both of the input
                  tables (FULL OUTER JOIN)

                * all1: An output row for each matched or unmatched row in table  1  (LEFT  OUTER
                  JOIN)

                * all2:  An  output row for each matched or unmatched row in table 2 (RIGHT OUTER
                  JOIN)

                * 1not2: An output row only for rows which appear in the first table but are  not
                  matched in the second table

                * 2not1: An output row only for rows which appear in the second table but are not
                  matched in the first table

                * 1xor2: An output row only for rows represented in one of the input  tables  but
                  not the other one

       find=all|best|best1|best2
              Determines what happens when a row in one table can be matched by more than one row
              in the other table. The options are:

                * all: All matches. Every match between the two tables is included in the result.
                  Rows from both of the input tables may appear multiple times in the result.

                * best:  Best match, symmetric. The best pairs are selected in a way which treats
                  the two tables symmetrically. Any input row which appears in one result pair is
                  disqualified  from  appearing  in  any other result pair, so each row from both
                  input tables will appear in at most one row in the result.

                * best1: Best match for each Table 1 row. For each row in table 1, only the  best
                  match from table 2 will appear in the result. Each row from table 1 will appear
                  a maximum of once in the result, but rows from  table  2  may  appear  multiple
                  times.

                * best2:  Best match for each Table 2 row. For each row in table 2, only the best
                  match from table 1 will appear in the result. Each row from table 2 will appear
                  a  maximum  of  once  in  the result, but rows from table 1 may appear multiple
                  times.
               The differences between best, best1 and best2 are a bit  subtle.  In  cases  where
              it's  obvious  which object in each table is the best match for which object in the
              other, choosing betwen these options  will  not  affect  the  result.  However,  in
              crowded  fields  (where  the  distance between objects within one or both tables is
              typically similar to or smaller than the specified match radius)  it  will  make  a
              difference.  In this case one of the asymmetric options (best1 or best2) is usually
              more appropriate than best, but you'll have to think about which of them suits your
              requirements.  The performance (time and memory usage) of the match may also differ
              between these options, especially if one table is much bigger than the other.

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-TSKYMATCH2(1)