Provided by: stilts_3.1.5-1_all bug

NAME

       stilts-pixsample - Samples from a HEALPix pixel data file

SYNOPSIS

       stilts pixsample [in=<table>] [ifmt=<in-format>] [icmd=<cmds>] [pixdata=<pix-table>]
                        [pfmt=<in-format>] [pcmd=<cmds>] [ocmd=<cmds>]
                        [omode=out|meta|stats|count|cgi|discard|topcat|samp|tosql|gui] [out=<out-
                        table>] [ofmt=<out-format>] [pixorder=nested|ring|(auto)]
                        [stat=point|mean] [lon=<expr>] [lat=<expr>]
                        [insys=icrs|fk5|fk4|galactic|supergalactic|ecliptic]
                        [pixsys=icrs|fk5|fk4|galactic|supergalactic|ecliptic] [radius=<expr>]

DESCRIPTION

       pixsample  samples  data  at  the sky position represented by each row from an all-sky map
       contained in a HEALPix-format pixel data file. Such files are actually tables (usually  in
       FITS  format)  in which the row number corresponds to a HEALPix pixel index, and the pixel
       values are cell contents; one or more columns may be present containing values for one  or
       more  all-sky  maps.  The  result  of  this  command is to add a column to the input table
       representing the pixel data at the position of each input row for each of the data columns
       in the HEALPix table.

       This  command does not attempt to convert between coordinate systems except as instructed,
       so it is important to know what coordinate system the HEALPix file is in, and ensure  that
       the  coordinates  supplied  from  the  input table match this. You may need to examine the
       documentation or headers of the HEALPix file in question to find  out.  See  the  Examples
       section for some examples.

       There  is  a choice of how the sampling is done; the simplest way is just to use the value
       of the pixel covering the indicated position. An alternative is to average over a disc  of
       given  radius  (perhaps  a  function of the input row). Other options (e.g. max/min) could
       easily be added.

       Although HEALPix is not a common format for storing image data in general, it is used  for
       storing a number of important all-sky data sets such as the WMAP results and Schlegel dust
       maps. The NASA LAMBDA (Legacy Archive for Microwave Background Data Analysis) archive  has
       a  number of maps in a suitable format, including foreground data like predicted reddening
       as well as CMB maps.

OPTIONS

       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.

       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.

       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.

       pixdata=<pix-table>
              The  location  of the table containing the pixel data. The data must be in the form
              of a HEALPix table, with one pixel per  row  in  HEALPix  order.  These  files  are
              typically,  but  not necessarily, FITS tables. A filename or URL may be used, but a
              local file will be more efficient.

              Some HEALPix format FITS tables seem to have rows which contain 1024-element arrays
              of  pixels  instead  of  single pixel values. This (rather perverse?) format is not
              currently supported here, but if there is demand support could be added.

       pfmt=<in-format>
              File format for the HEALPix pixel data table. This is usually, but not necessarily,
              FITS.

       pcmd=<cmds>
              Specifies  processing to be performed on pixel data table as specified by parameter
              pixdata, 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".

       pixorder=nested|ring|(auto)
              Selects the pixel ordering scheme used by  the  pixel  data  file.  There  are  two
              different  ways  of ordering pixels in a HEALPix file, "ring" and "nested", and the
              sampler needs to know which one is in use. If you know which is in use, choose  the
              appropriate  value for this parameter; if (auto) is used it will attempt to work it
              out from headers in the file (the ORDERING header). If no reliable ordering  scheme
              can be determined, the command will fail with an error.

       stat=point|mean
              Determines  how  the  pixel values will be sampled to generate an output value. The
              options are:

                * point: Uses the value at the pixel covering the supplied position. In this case
                  the radius parameter is not used.

                * mean:  Averages  the  values  over  all the pixels within a radius given by the
                  radius parameter. This averaging is somewhat approximate; all pixels which  are
                  mostly within the radius are averaged with equal weights.

       lon=<expr>
              Expression  which  evaluates  to  the  longitude coordinate in degrees in the input
              table at which positions are to be sampled from the pixel  data  table.  This  will
              usually  be  the  name  or  ID  of  a  column  in the input table, or an expression
              involving one. If this coordinate does not match the coordinate system used by  the
              pixel  data  table,  both coordinate systems must be set using the insys and pixsys
              parameters.

       lat=<expr>
              Expression which evaluates to the latitude coordinate in degrees in the input table
              at  which  positions are to be sampled from the pixel data table. This will usually
              be the name or ID of a column in the input table, or an expression  involving  one.
              If  this  coordinate  does  not  match the coordinate system used by the pixel data
              table, both coordinate systems must be set using the insys and pixsys parameters.

       insys=icrs|fk5|fk4|galactic|supergalactic|ecliptic
              Specifies the sky coordinate system in which sample positions are provided  by  the
              lon/lat parameters. If the sample positions are given in the same coordinate system
              as that given by the pixel data table, both the insys and pixsys parameters may  be
              set null.

              The available coordinate systems are:

                * icrs: ICRS (Hipparcos) (Right Ascension, Declination)

                * fk5: FK5 J2000.0 (Right Ascension, Declination)

                * fk4: FK4 B1950.0 (Right Ascension, Declination)

                * galactic: IAU 1958 Galactic (Longitude, Latitude)

                * supergalactic: de Vaucouleurs Supergalactic (Longitude, Latitude)

                * ecliptic: Ecliptic (Longitude, Latitude)

       pixsys=icrs|fk5|fk4|galactic|supergalactic|ecliptic
              Specifies  the sky coordinate system used for the HEALPix data in the pixdata file.
              If the sample positions are given in the same coordinate system as  that  given  by
              the pixel data table, both the insys and pixsys parameters may be set null.

              The available coordinate systems are:

                * icrs: ICRS (Hipparcos) (Right Ascension, Declination)

                * fk5: FK5 J2000.0 (Right Ascension, Declination)

                * fk4: FK4 B1950.0 (Right Ascension, Declination)

                * galactic: IAU 1958 Galactic (Longitude, Latitude)

                * supergalactic: de Vaucouleurs Supergalactic (Longitude, Latitude)

                * ecliptic: Ecliptic (Longitude, Latitude)

       radius=<expr>
              Determines  the radius in degrees over which pixels will be sampled to generate the
              output statistic in accordance with the value of  the  stat  parameter.  This  will
              typically  be  a  constant  value,  but  it may be an algebraic expression based on
              columns from the input table.

              Not used if stat=point.

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-PIXSAMPLE(1)