Ubuntu Manpage: stilts-tskymap - Calculates sky density maps

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NAME

       stilts-tskymap - Calculates sky density maps

SYNOPSIS

       stilts tskymap [ifmt=<in-format>] [istream=true|false] [in=<table>] [icmd=<cmds>] [ocmd=<cmds>]
                      [omode=out|meta|stats|count|cgi|discard|topcat|samp|tosql|gui] [out=<out-table>]
                      [ofmt=<out-format>] [lon=<expr/deg>] [lat=<expr/deg>]
                      [tiling=hpx<K>|healpixnest<K>|healpixring<K>|htm<K>] [count=true|false] [cols=<expr> ...]
                      [combine=sum|mean|median|min|max|stdev|count|hit] [complete=true|false]

DESCRIPTION

       tskymap  calculates  a  weighted  density  map  (or,  to put it another way, a histogram) on the sky from
       columns of an input table. The sky is divided up into some discrete set of tiles according to a specified
       tessellation  scheme (currently HEALPix or HTM are supported), and the required quantities are aggregated
       into bins corresponding to these tiles. The output table has a column giving the pixel index  identifying
       each tile, plus one or more columns each representing an aggregation of a quantity from the input table.

       By  default  the  number  of  rows from the input table falling within each tile is included as the first
       column in the output table. But by specifying the cols and combine parameters you can  add  more  columns
       giving the sum, mean, median or other statistics of input table columns or expressions as well.

       The  output  table  can  then,  for  instance,  be plotted using plot2sky's healpix layer type (though an
       alternative is to do that plot directly using a skydensity layer).

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.

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).

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 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.

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|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

* 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".

lon=<expr/deg>
Longitude in degrees for the position of each row in the input table. This may simply be a column
name, or it may be an algebraic expression as explained in SUN/256. The sky system used here will
determine the grid on which the output map is built.

lat=<expr/deg>
Latitude in degrees for the position of each row in the input table. This may simply be a column
name, or it may be an algebraic expression as explained in SUN/256. The sky system used here will
determine the grid on which the output map is built.

tiling=hpx<K>|healpixnest<K>|healpixring<K>|htm<K>
Describes the sky tiling scheme that is in use. One of the following values may be used:

* hpxK: alias for healpixnestK

* healpixnestK: HEALPix using the Nest scheme at order K

* healpixringK: HEALPix using the Ring scheme at order K

* htmK: Hierarchical Triangular Mesh at level K
So for instance hpx5 or healpixnest5 would both indicate the HEALPix NEST tiling scheme at order
5.

At level K, there are 12*4^K HEALPix pixels, or 8*4^K HTM pixels on the sky. More information
about these tiling schemes can be found at the HEALPix and HTM web sites.

count=true|false
Controls whether a COUNT column is added to the output table along with any other columns that may
have been requested. If included, this reports the number of rows from the input table that fell
within the corresponding bin.

cols=<expr> ...
Selects the columns to be aggregated into bins. The value is a space-separated list of items,
where each item may be either a column name or an expression using the expression language. The
output table will have one column for each of the items in this list.

* sum: the sum of all the combined values

* mean: the mean of the combined values

* median: the median of the combined values (may be slow)

* 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

* count: the number of non-blank values (weight is ignored)

* hit: 1 if any values present, NaN otherwise (weight is ignored)

complete=true|false
Determines whether the output table contains a row for every pixel in the tiling, or only the rows
for pixels in which some of the input data fell.

The value of this parameter may affect performance as well as output. If you know that most pixels
on the sky will be covered, it's probably a good idea to set this true, and if you know that only
a small patch of sky will be covered, it's better to set it false.

VERSION

       STILTS version 3.1-2-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-TSKYMAP(1)