Provided by: stilts_3.5.1-2_all 
NAME
stilts-tmatchn - Crossmatches multiple tables using flexible criteria
SYNOPSIS
stilts tmatchn [nin=<count>] [ifmtN=<in-format>] [inN=<tableN>] [icmdN=<cmds>]
[ocmd=<cmds>]
[omode=out|meta|stats|count|checksum|cgi|discard|topcat|samp|tosql|gui]
[out=<out-table>] [ofmt=<out-format>] [multimode=pairs|group] [iref=<table-
index>] [matcher=<matcher-name>] [params=<match-params>] [tuning=<tuning-
params>] [valuesN=<expr-list>] [joinN=default|match|nomatch|always]
[fixcols=none|dups|all] [suffixN=<label>] [progress=none|log|time|profile]
[runner=parallel|parallel<n>|parallel-all|sequential|classic|partest]
DESCRIPTION
tmatchn performs efficient and flexible crossmatching between multiple tables. 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.
Since the match criteria define what counts as a match between two objects, it is not
immediately obvious what is meant by a multi-table match. In fact the command can work in
one of two distinct modes, controlled by the multimode parameter. In pairs mode, one table
(by default the first input table) is designated the reference table, and pair matches
between each of the other tables and that one are identified. In group mode groups of
objects from all the input tables are identified, as discussed in SUN/256. Currently, in
both cases an output matched row cannot contain more than one object from each input
table. Options for output of multiple rows per input table per match may be forthcoming in
future releases if there is demand.
tmatchn is intended for use with more than two input tables - see tmatch1 and tmatch2 for
1- and 2-table crossmatching respectively.
OPTIONS
nin=<count>
The number of input tables for this task. For each of the input tables N there will
be associated parameters ifmtN, inN and icmdN.
ifmtN=<in-format>
Specifies the format of input table #N as specified by parameter inN. 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.
inN=<tableN>
The location of input table #N. 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 ifmtN 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.
icmdN=<cmds>
Specifies processing to be performed on input table #N as specified by parameter
inN, 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 alternatively 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. A backslash character '\fR' at the
end of a line joins it with the following line.
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 alternatively 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. A backslash character '\fR' at the
end of a line joins it with the following line.
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".
multimode=pairs|group
Defines what is meant by a multi-table match. There are two possibilities:
* pairs: Each output row corresponds to a single row of the reference table (see
parameter iref) and contains entries from other tables which are pair matches
to that. If a reference table row matches multiple rows from one of the other
tables, only the best one is included.
* group: Each output row corresponds to a group of entries from the input tables
which are mutually linked by pair matches between them. This means that
although you can get from any entry to any other entry via one or more pair
matches, there is no guarantee that any entry is a pair match with any other
entry. No table has privileged status in this case. If there are multiple
entries from a given table in the match group, an arbitrary one is chosen for
inclusion (there is no unique way to select the best). See SUN/256 for more
discussion.
Note that which rows actually appear in the output is also influenced by the joinN
parameter.
iref=<table-index>
If multimode=pairs this parameter gives the index of the table in the input table
list which is to serve as the reference table (the one which must be matched by
other tables). Ignored in other modes.
Row ordering in the output table is usually tidiest if the default setting of 1 is
used (i.e. if the first input table is used as the reference table).
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.
valuesN=<expr-list>
Defines the values from table N 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.
joinN=default|match|nomatch|always
Determines which rows from input table N are included in the output table. The
matching algorithm determines which of the rows in each of the input tables
correspond to which rows in the other input tables, and this parameter determines
what to do with that information.
The default behaviour is that a row will appear in the output table if it
represents a match of rows from two or more of the input tables. This can be
altered on a per-input-table basis however by choosing one of the non-default
options below:
* match: Rows are included only if they contain an entry from input table N.
* nomatch: Rows are included only if they do not contain an entry from input
table N.
* always: Rows are included if they contain an entry from input table N
(overrides any match and nomatch settings of other tables).
* default: Input table N has no special effect on whether rows are included.
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.
suffixN=<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 table N.
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.
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 3.5.1-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-TMATCHN(1)