Provided by: stilts_3.1.5-1_all bug

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|sum-per-unit|count|count-per-
                      unit|mean|median|min|max|stdev|hit]
                      [perunit=steradian|degree2|arcmin2|arcsec2|mas2|uas2] [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, 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|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.

       combine=sum|sum-per-unit|count|count-per-unit|mean|median|min|max|stdev|hit
              Defines how 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 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

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

              For density-like values (count-per-unit, sum-per-unit) the scaling is  additionally
              influenced by the perunit parameter.

       perunit=steradian|degree2|arcmin2|arcsec2|mas2|uas2
              Defines  the  unit  of  sky  area  used for scaling density-like combinations (e.g.
              combine=count-per-unit or sum-per-unit). If the  combination  mode  is  calculating
              values  per  unit area this configures the area scale in question. For non-density-
              like combination modes (e.g. combine=sum or mean) it has no effect.

              Possible values are:

                * steradian: steradian

                * degree2: square degree

                * arcmin2: square arcminute

                * arcsec2: square arcsecond

                * mas2: square milliarcsec

                * uas2: square microarcsec

       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.

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-doc/sun256/index.html

VERSION

       STILTS version 3.1-5-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)