Ubuntu Manpage: stilts-tmatch1 - Performs a crossmatch internal to a single table

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 com‐
       bination 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 con‐
tains 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 cho‐
sen.

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 addi‐
tional 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 out‐
put 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

* 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 opera‐
tions 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 auto‐
matically. 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 neces‐
sary 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 au‐
tomatically if that is the best thing to do. However it can sometimes result in less resource us‐
age 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 ex‐
plicitly 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 com‐
mands described in SUN/256. If more than one is given, they must be separated by semicolon charac‐
ters (";"). 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.

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 pa‐
rameters. 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.