Provided by: stilts_3.4.7-4_all 
NAME
stilts-tmatch1 - Performs a crossmatch internal to a single table
SYNOPSIS
stilts tmatch1 [matcher=<matcher-name>] [params=<match-params>] [tuning=<tuning-params>]
[values=<expr-list>] [action=identify|keep0|keep1|wide2|wideN]
[progress=none|log|time|profile] [runner=parallel|parallel<n>|parallel-
all|sequential|classic|partest] [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>]
DESCRIPTION
tmatch1 performs efficient and flexible crossmatching between the rows of a single table.
It can match rows on the basis of their relative position in the sky, or alternatively
using many other criteria such as separation in in some isotropic or anisotropic Cartesian
space, identity of a key value, or some combination of these; the full range of match
criteria is dicussed in SUN/256.
The basic task performed by the intra-table matcher is to identify groups of rows within
the table which match each other. See SUN/256 for an explanation of exactly what
consitutes a match group. The result of identifying these groups is expressed as an output
table in one of a variety of ways, specified by the action parameter. These options
include marking group membership in added columns and eliminating some or all rows which
form part of a match group.
OPTIONS
matcher=<matcher-name>
Defines the nature of the matching that will be performed. Depending on the name
supplied, this may be positional matching using celestial or Cartesian coordinates,
exact matching on the value of a string column, or other things. A list and
explanation of the available matching algorithms is given in SUN/256. The value
supplied for this parameter determines the meanings of the values required by the
params, values* and tuning parameter(s).
params=<match-params>
Determines the parameters of this match. This is typically one or more tolerances
such as error radii. It may contain zero or more values; the values that are
required depend on the match type selected by the matcher parameter. If it contains
multiple values, they must be separated by spaces; values which contain a space can
be 'quoted' or "quoted".
tuning=<tuning-params>
Tuning values for the matching process, if appropriate. It may contain zero or more
values; the values that are permitted depend on the match type selected by the
matcher parameter. If it contains multiple values, they must be separated by
spaces; values which contain a space can be 'quoted' or "quoted". If this optional
parameter is not supplied, sensible defaults will be chosen.
values=<expr-list>
Defines the values from the input table which are used to determine whether a match
has occurred. These will typically be coordinate values such as RA and Dec and
perhaps some per-row error values as well, though exactly what values are required
is determined by the kind of match as determined by matcher. Depending on the kind
of match, the number and type of the values required will be different. Multiple
values should be separated by whitespace; if whitespace occurs within a single
value it must be 'quoted' or "quoted". Elements of the expression list are commonly
just column names, but may be algebraic expressions calculated from zero or more
columns as explained in SUN/256.
action=identify|keep0|keep1|wide2|wideN
Determines the form of the table which will be output as a result of the internal
match.
* identify: The output table is the same as the input table except that it
contains two additional columns, GroupID and GroupSize, following the input
columns. Each group of rows which matched is assigned a unique integer,
recorded in the GroupID column, and the size of each group is recorded in the
GroupSize column. Rows which don't match any others (singles) have null values
in both these columns.
* keep0: The result is a new table containing only "single" rows, that is ones
which don't match any other rows in the table. Any other rows are thrown out.
* keep1: The result is a new table in which only one row (the first in the input
table order) from each group of matching ones is retained. A subsequent intra-
table match with the same criteria would therefore show no matches.
* wideN: The result is a new "wide" table consisting of matched rows in the input
table stacked next to each other. Only groups of exactly N rows in the input
table are used to form the output table; each row of the output table consists
of the columns of the first group member, followed by the columns of the second
group member and so on. The output table therefore has N times as many columns
as the input table. The column names in the new table have _1, _2, ... appended
to them to avoid duplication.
progress=none|log|time|profile
Determines whether information on progress of the match should be output to the
standard error stream as it progresses. For lengthy matches this is a useful
reassurance and can give guidance about how much longer it will take. It can also
be useful as a performance diagnostic.
The options are:
* none: no progress is shown
* log: progress information is shown
* time: progress information and some time profiling information is shown
* profile: progress information and limited time/memory profiling information are
shown
runner=parallel|parallel<n>|parallel-all|sequential|classic|partest
Selects the threading implementation. The options are currently:
* parallel: uses multithreaded implementation for large tables, with default
parallelism, which is the smaller of 6 and the number of available processors
* parallel<n>: uses multithreaded implementation for large tables, with
parallelism given by the supplied value <n>
* parallel-all: uses multithreaded implementation for large tables, with a
parallelism given by the number of available processors
* sequential: uses multithreaded implementation but with only a single thread
* classic: uses legacy sequential implementation
* partest: uses multithreaded implementation even when tables are small
The parallel* options should normally run faster than sequential or classic (which
are provided mainly for testing purposes), at least for large matches and where
multiple processing cores are available.
The default value "parallel" is currently limited to a parallelism of 6 since
larger values yield diminishing returns given that some parts of the matching
algorithms run sequentially (Amdahl's Law), and using too many threads can
sometimes end up doing more work or impacting on other operations on the same
machine. But you can experiment with other concurrencies, e.g. "parallel16" to run
on 16 cores (if available) or "parallel-all" to run on all available cores.
The value of this parameter should make no difference to the matching results. If
you notice any discrepancies please report them.
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".
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 3.4.7-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-TMATCH1(1)