Provided by: stilts_3.4.9-5_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|stdev_pop|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-dimen‐
sional histograms, of the values in an input table, and outputs the result as an, optionally sparse, ta‐
ble 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 ag‐
gregation 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, es‐
pecially 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 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 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 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".
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 corre‐
sponding 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, ... dimen‐
sion. 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, ... di‐
mension. An attempt is made to use round numbers for bin sizes so the bin counts may not be exact‐
ly 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 parame‐
ter. If omitted, the value specified for that parameter will be used.
* <name>: (optional) name of output column; if omitted, the <expr> value (perhaps somewhat sani‐
tised) 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", yield‐
ing an output column named "COUNT").
combine=sum|sum-per-unit|count|count-per-unit|mean|median|Q1|Q3|min|max|stdev|stdev_pop|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
* stdev_pop: the population 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 op‐
tions 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 sup‐
plied 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 oper‐
ations 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 di‐
rectly from a spinning disk, for instance because the file is too large to fit in RAM, then se‐
quential 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 no‐
tice 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 3.4.9-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
Mark Taylor (Bristol University)
Mar 2017 STILTS-TGRIDMAP(1)