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This control is experimental.
As currently implemented it lacks some important features.
It may be improved or withdrawn in a future version.
The Spectrogram Layer Control (
)
plots a spectrum at successive (usually, but not necessarily,
regularly-spaced) points in a time series.
It is only available for the experimental
Time Plot Window.
Time Plot window with a Spectrogram layer
This control has two tabs, Data and Style,
described below.
Spectrogram control Data tab
The Data tab allows you to specify which values from
a table will generate a spectrogram.
It has the following fields:
-
Table
- The table supplying the data.
-
Time
- A table column or expression giving the epoch coordinate at which
spectra are located.
This should normally be a time-typed column;
if it is simply of numeric type it will be interpreted as seconds
since 1 Jan 1970.
-
Spectrum
- An array-valued table column giving the spectral data.
-
TimeWidth
- A table column or expression (variable or constant) giving the
temporal coverage of a plotted spectrum.
If not filled in, it is assumed to be the most common
(median) difference between time points.
-
Row Subset
- The subset for which the spectrum should
be plotted. To plot multiple subsets (not usually useful with this
kind of plot) you would need multiple spectrogram layer controls
in the stack.
Spectrogram control Style tab
The Style allows you to configure the way the spectrogram
is plotted. It has the following fields:
-
Spectral Shader
- Select the colour map from a list of options.
-
Shader Clip
- Select a sub-range of the full colour map above.
By default the whole colour map is used, but if you want the range
of colours in the plot to be formed from only a part of the colour
band shown in the Shader control,
you can move the handles in from the end of this slider.
-
Shader Flip
- Whether the spectral values should map forwards or backwards
into the colour map.
-
Shader Quantise
- Allows the colour map to be quantised.
By default, the colour map is effectively continuous.
If you slide the slider to the right, the map will be split into
a decreasing number of discrete colours. This can be used to generate
a contour-like efect, and may make it easier to trace the boundaries
of regions of interest by eye.
-
Scaling
- Determines the function used to map the range of spectral data values
onto the colour map.
Options are linear,
logarithmic,
square and
square root.
-
Spectral Subrange
- Adjusts the range of the spectral coordinate over which the
colour map is applied. By default the colour map is scaled using
limits found from the spectral data values themselves,
but you can restrict the range using this slider.
-
Null Colour
- What colour should be used to represent spectral samples with a null
value.
If the associated Hide option is selected,
then those points will not appear in the plot at all (they will be
transparent).
Next Previous Up Contents
Next: Function Layer Control
Up: Layer Controls
Previous: Histogram Layer Control
TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page:
http://www.starlink.ac.uk/topcat/
Author email:
m.b.taylor@bristol.ac.uk
Mailing list:
topcat-user@bristol.ac.uk