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8.3.23 spectrogram

Plots spectrograms. A spectrogram is a sequence of spectra plotted as vertical 1-d images, each one plotted at a different horizontal coordinate.

This specialised layer is only available for time plots.

Usage Overview:

   layerN=spectrogram spectromapN=rainbow|rainbow2|pastel|...
                      spectroclipN=<lo>,<hi> spectroflipN=true|false
                      spectroquantN=<number>
                      spectrofuncN=log|linear|sqrt|square spectrosubN=<lo>,<hi>
                      spectronullcolorN=<rrggbb>|red|blue|... tN=<time-expr>
                      spectrumN=<array-expr> twidthN=<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.

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]

spectroclipN = <lo>,<hi>       (Subrange)
Defines a subrange of the colour ramp to be used for Spectral shading. The is specified as a (low,high) comma-separated pair of two numbers between 0 and 1.

If the full range 0,1 (the default) is used, the whole range of colours specified by the selected shader will be used. But if, for instance a value of 0,0.5 is given, only those colours at the left hand end of the ramp will be seen.

[Default: 0,1]

spectroflipN = true|false       (Boolean)
If true, the colour map on the Spectral axis will be reversed.

[Default: false]

spectrofuncN = log|linear|sqrt|square       (Scaling)
Defines the way that values in the Spectral range are mapped to the selected colour ramp.

The available options are:

[Default: linear]

spectromapN = rainbow|rainbow2|pastel|...       (Shader)
Color map used for Spectral axis shading.

A mixed bag of colour ramps are available: rainbow, rainbow2, pastel, accent, gnuplot, gnuplot2, cubehelix, specxby, set1, paired, cyan-magenta, red-blue, brg, heat, cold, light, colour, greyscale, standard, rainbow3, mask, hue, transparency, intensity, rgb_red, rgb_green, rgb_blue, hsv_h, hsv_s, hsv_v, yuv_y, yuv_u, yuv_v, bugn, bupu, orrd, pubu, purd. Note: many of these, including rainbow-like ones, are frowned upon by the visualisation community.

[Default: rainbow]

spectronullcolorN = <rrggbb>|red|blue|...       (Color)
The color of points with a null value of the Spectral coordinate.

The value may be a six-digit hexadecimal number giving red, green and blue intensities, e.g. "ff00ff" for magenta. Alternatively it may be the name of one of the pre-defined colors. These are currently red, blue, green, grey, magenta, cyan, orange, pink, yellow, black, white.

If the value is null, then points with a null Spectral value will not be plotted at all.

[Default: grey]

spectroquantN = <number>       (Double)
Allows the colour map used for the Spectral axis to be quantised. If an integer value N is chosen then the colour map will be viewed as N discrete evenly-spaced levels, so that only N different colours will appear in the plot. This can be used to generate a contour-like effect, and may make it easier to trace the boundaries of regions of interest by eye.

If left blank, the colour map is nominally continuous (though in practice it may be quantised to a medium-sized number like 256).

spectrosubN = <lo>,<hi>       (Subrange)
Defines a normalised adjustment to the data range of the Spectral axis. The value may be specified as a comma-separated pair of two numbers, giving the lower and upper bounds of the range of of interest respectively. This sub-range is applied to the data range that would otherwise be used, either automatically calculated or explicitly supplied; zero corresponds to the lower bound and one to the upper.

The default value "0,1" therefore has no effect. The range could be restricted to its lower half with the value 0,0.5.

[Default: 0,1]

spectrumN = <array-expr>       (String)
Provides an array of spectral samples at each data point. The value must be a numeric array (e.g. the value of an array-valued column).

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

tN = <time-expr>       (String)
Time coordinate.

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

twidthN = <num-expr>       (String)
Range on the Time axis over which the spectrum is plotted. If no value is supplied, an attempt will be made to determine it automatically by looking at the spacing of the Time coordinates plotted in the spectrogram.

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


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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@bristol.ac.uk