Ubuntu Manpage: stilts-tmatchn - Crossmatches multiple tables using flexible criteria

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  separa‐
       tion 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, con‐
       trolled by the multimode parameter. In pairs mode, one table (by default the first input table) is desig‐
       nated 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.  Cur‐
       rently,  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 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.

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 ex‐
plicitly 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 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 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.

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.

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 mutu‐
ally 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 inclu‐
sion (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 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.

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 dif‐
ferent. 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 in‐
put 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 in‐
dicate 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

* 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.

VERSION

       STILTS version 3.4.9-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