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8.3.27 healpix

Plots a table representing HEALPix pixels on the sky. Each row represents a single HEALPix tile, and a value from that row is used to colour the corresponding region of the sky plot.

The way that data values are mapped to colours is usually controlled by options at the level of the plot itself, rather than by per-layer configuration.

Usage Overview:

   layerN=healpix datalevelN=<int-value> datasysN=<value>
                  viewsysN=equatorial|galactic|supergalactic|ecliptic
                  degradeN=<int-value> combinerN=<value> transparencyN=0..1
                  healpixN=<num-expr> valueN=<num-expr> inN=<table>
                  ifmtN=<in-format> istreamN=true|false icmdN=<cmds>

All the parameters listed here affect only the relevant layer, identified by the suffix N.

Example:

   stilts plot2sky layer1=healpix in1=simbad-hpx8.fits healpix1=HPX8 value1=NBREF
                   datalevel1=8 degrade1=2
                   projection=aitoff datasys1=equatorial viewsys=galactic labelpos=none
                   auxfunc=log auxmap=cold auxflip=true auxvisible=false auxclip=0,1
                   xpix=500 ypix=250

combinerN = <value>       (Combiner)
Defines how pixel values will be combined if they are degraded to a lower resolution than the data HEALPix level. This only has any effect if degrade>0.

[Default: sum]

datalevelN = <int-value>       (Integer)
HEALPix level of the (implicit or explicit) tile indices. Legal values are between 0 (12 pixels) and 13 (805306368 pixels). If a negative value is supplied (the default), then an attempt is made to determine the correct level from the data.

[Default: -1]

datasysN = <value>       (SkySys)
The sky coordinate system to which the HEALPix grid used by the input pixel file refers.

[Default: equatorial]

degradeN = <int-value>       (Integer)
Allows the HEALPix grid to be drawn at a less detailed level than the level at which the input data are supplied. A value of zero (the default) means that the HEALPix tiles are painted with the same resolution as the input data, but a higher value will degrade resolution of the plot tiles; each plotted tile will correspond to 4^degrade input tiles. The way that values are combined within each painted tile is controlled by the combiner value.

[Default: 0]

healpixN = <num-expr>       (String)
HEALPix index indicating the sky position of the tile whose value is plotted. If not supplied, the assumption is that the supplied table contains one row for each HEALPix tile at a given level, in ascending order.

The value is a numeric algebraic expression based on column names as described in Section 10.

icmdN = <cmds>       (ProcessingStep[])
Specifies processing to be performed on the layer N input table as specified by parameter inN. The value of this parameter is one or more of the filter commands described in Section 6.1. 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.

ifmtN = <in-format>       (String)
Specifies the format of the input table as specified by parameter inN. The known formats are listed in Section 5.2.1. 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.

[Default: (auto)]

inN = <table>       (StarTable)
The location of the input table. This may take one of the following forms: In any case, compressed data in one of the supported compression formats (gzip, Unix compress or bzip2) will be decompressed transparently.
istreamN = true|false       (Boolean)
If set true, the input table specified by the inN parameter will be read as a stream. It is necessary to give the ifmtN 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).

[Default: false]

transparencyN = 0..1       (Double)
Transparency with which components are plotted, in the range 0 (opaque) to 1 (invisible). The value is 1-alpha.

[Default: 0]

valueN = <num-expr>       (String)
Value of HEALPix tile, determining the colour which will be plotted.

The value is a numeric algebraic expression based on column names as described in Section 10.

viewsysN = equatorial|galactic|supergalactic|ecliptic       (SkySys)
The sky coordinate system used for the generated plot.

Choice of this value goes along with the data coordinate system that may be specified for plot layers. If unspecified, a generic longitude/latitude system is used, and all lon/lat coordinates in the plotted data layers are assumed to be in the same system. If a value is supplied for this parameter, then a sky system must (implicitly or explicitly) be supplied for each data layer, and the coordinates are converted from data to view system before being plotted.

The available options are:

[Default: equatorial]


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Next: skygrid
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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk