Provided by: stilts_3.4.7-4_all 
NAME
stilts-tgridmap - Calculates N-dimensional density maps
SYNOPSIS
stilts tgridmap [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>] [coords=<expr> ...] [logs=true|false
...] [bounds=[<lo>]:[<hi>] ...] [binsizes=<size> ...] [nbins=<num> ...]
[cols=<expr>[;<combiner>[;<name>]] ...] [combine=sum|sum-per-
unit|count|count-per-unit|mean|median|Q1|Q3|min|max|stdev|hit]
[sparse=true|false] [runner=sequential|parallel|parallel<n>|partest]
DESCRIPTION
tgridmap scans an input table to create one or more N-dimensional density maps, or
equivalently N-dimensional histograms, of the values in an input table, and outputs the
result as an, optionally sparse, table containing a row for each grid cell. The
maps/histograms can optionally be weighted by some quantity from the input table, and
various options such as summing, averaging and counting are available for aggregation of
inputs into the output bins.
The supplied coords parameter defines which N numeric columns of the input table form the
coordinates of the bin grid, and the cols parameter defines which quantities are
aggregated into each bin. Either the binsizes or nbins parameter must be supplied to
define the extents of the bins on each axis. The output table contains a row for each bin,
with columns giving the central (and upper/lower bound) values of each grid coordinate,
and a column for each aggregated value. The rows are output in first-coordinate-slowest
sequence, and the sparse parameter determines whether a row is written for every cell in
the hypercube defined by the grid dimensions, or only for those cells with non-blank data.
The tabular form of the output may not be the most appropriate or compact way to write a
density map, especially for multi-dimensional grids, but it means the output can be
manipulated later by other STILTS commands or by TOPCAT. To do a similar job with more
compact output, see tcube. See also tskymap, which does the same thing for sky geometry
(and is probably a better choice if you find yourself accumulating onto a longitude-
latitude grid).
OPTIONS
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".
coords=<expr> ...
Defines the dimensions of the grid over which accumulation will take place. The
form of this value is a space-separated list of words each giving a column name or
algebraic expression defining one of the dimensions of the output grid. For a
1-dimensional histogram, only one value is required.
logs=true|false ...
Determines whether each coordinate axis is linear or logarithmic. By default the
grid axes are linear, but if this parameter is supplied with one or more true
values, the bins on the corresponding axes are assigned logarithmically instead.
If supplied, this parameter must have the same number of words as the coords
parameter.
bounds=[<lo>]:[<hi>] ...
Gives the bounds for each dimension of the cube in data coordinates. The form of
the value is a space-separated list of words, each giving an optional lower bound,
then a colon, then an optional upper bound, for instance "1:100 0:20" to represent
a range for two-dimensional output between 1 and 100 of the first coordinate (table
column) and between 0 and 20 for the second. Either or both numbers may be omitted
to indicate that the bounds should be determined automatically by assessing the
range of the data in the table. A null value for the parameter indicates that all
bounds should be determined automatically for all the dimensions.
If any of the bounds need to be determined automatically in this way, two passes
through the data will be required, the first to determine bounds and the second to
calculate the map.
If supplied, this parameter must have the same number of words as the coords
parameter.
binsizes=<size> ...
Gives the extent of of the data bins in each dimension in data coordinates. The
form of the value is a space-separated list of values, giving a list of extents for
the first, second, ... dimension. Either this parameter or the nbins parameter must
be supplied.
If supplied, this parameter must have the same number of words as the coords
parameter.
nbins=<num> ...
Gives the approximate number of bins in each dimension. The form of the value is a
space-separated list of integers, giving the number of bins for the output
histogram in the first, second, ... dimension. An attempt is made to use round
numbers for bin sizes so the bin counts may not be exactly as specified. Either
this parameter or the binsizes parameter must be supplied.
If supplied, this parameter must have the same number of words as the coords
parameter.
cols=<expr>[;<combiner>[;<name>]] ...
Defines the quantities to be calculated. The value is a space-separated list of
items, one for each aggregated column in the output table.
Each item is composed of one, two or three tokens, separated by semicolon (";")
characters:
* <expr>: (required) column name or expression using the expression language for
the quantity to be aggregated.
* <combiner>: (optional) combination method, using the same options as for the
combine parameter. If omitted, the value specified for that parameter will be
used.
* <name>: (optional) name of output column; if omitted, the <expr> value (perhaps
somewhat sanitised) will be used.
It is often sufficient just to supply a space-separated list of input table column
names for this parameter, but the additional syntax may be required for instance if
it's required to calculate both a sum and mean of the same input column.
The default value is "1;count;COUNT" which simply provides an unweighted histogram,
i.e. a count of the rows in each bin (aggregation of the value "1" using the
combination method "count", yielding an output column named "COUNT").
combine=sum|sum-per-unit|count|count-per-unit|mean|median|Q1|Q3|min|max|stdev|hit
Defines the default way that values contributing to the same density map bin are
combined together to produce the value assigned to that bin. Possible values are:
* sum: the sum of all the combined values per bin
* sum-per-unit: the sum of all the combined values per unit of bin size
* count: the number of non-blank values per bin (weight is ignored)
* count-per-unit: the number of non-blank values per unit of bin size (weight is
ignored)
* mean: the mean of the combined values
* median: the median
* Q1: first quartile
* Q3: third quartile
* min: the minimum of all the combined values
* max: the maximum of all the combined values
* stdev: the sample standard deviation of the combined values
* hit: 1 if any values present, NaN otherwise (weight is ignored)
Note this value may be overridden on a per-column basis by the cols parameter.
sparse=true|false
Determines whether a row is written for every cell in the defined grid, or only for
those cells in which data appears in the input. The result will usually be more
compact if this is set false, but if you want to compare results from different
runs it may be convenient to set it true.
runner=sequential|parallel|parallel<n>|partest
Selects the threading implementation, i.e. to what extent processing is done in
parallel. The options are currently:
* sequential: runs using only a single thread
* parallel: runs using multiple threads for large tables, with parallelism given
by the number of available processors
* parallel<n>: runs using multiple threads for large tables, with parallelism
given by the supplied value <n>
* partest: runs using multiple threads even when tables are small (only intended
for testing purposes)
Using parallel processing can speed up execution considerably; however, depending
on the I/O operations required, it can also slow it down by disrupting patterns of
disk access. If the content of a file is on a solid state disk, or is already in
cache for instance because a similar command has been run recently, then parallel
will probably be faster. However, if the data is being read directly from a
spinning disk, for instance because the file is too large to fit in RAM, then
sequential or parallel<n> with a small <n> may be faster.
The value of this parameter should make only very tiny differences to the output
table. If you notice significant 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 3.4.7-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-TGRIDMAP(1)