Provided by: stilts_3.4.3-1_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|checksum|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>[;<combiner>[;<name>]] ...] [combine=sum|sum-per-
                      unit|count|count-per-unit|mean|median|Q1|Q3|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).

       In  the  case of HEALPix tiling, the result can also be output in a FITS file suitable for
       use by external applications that understand the  semi-standard  FITS-Healpix  convention.
       Note  in  this  case,  for maximum compatibility, the fits-healpix output format should in
       general be used.

       See also tgridmap, which does the same thing for N-dimensional grid geometry.

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".

       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>[;<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.

       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)

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

              Note this value may be overridden on a per-column basis by the cols 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/sun256/index.html

VERSION

       STILTS version 3.4.3-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)