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Density mode selection
The Density shading mode (
)
uses a configurable colour map
to indicate how many points are plotted over each other.
Specifically, it colours each pixel according to how many times that
pixel has has been covered by one of the shapes plotted by the layer
in question.
To put it another way, it generates a false-colour density map
with pixel granularity using a smoothing kernel of the form of
the shapes plotted by the layer.
The upshot is that you can see the plot density of points or other
shapes plotted.
This is like Auto mode, but with more
user-configurable options. The options are:
-
Map
- The colour map for displaying density values.
There are two types, relative and absolute.
Relative maps have names marked by a star ("*"), and alter the
basic dataset colour, for instance by darkening or lightening it,
while absolute maps (the rest) ignore the basic dataset colour altogether.
For a single-dataset plot, the absolute maps are best, but for
multiple subsets it may be less confusing to use a relative one.
-
Map Clip
- Select only a part of the colour map selected 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.
-
Log
- Selects whether the colour map should be applied linearly or
logarithmically to the range of densities. The default is logarithmic.
-
Flip
- Selects whether the colour map should be applied forwards or
backwards to the range of densities.
-
Sub-range
- Adjusts the density range over which the colour
map is applied. By default the colour map is scaled using limits
found from the data density in the plot (the most dense few pixels are
ignored), but you can restrict the range using this slider.
Exporting:
When exported to vector formats, the output is automatically forced to a
bitmap for Density-mode layers.
In the case of PostScript, this completely obscures any previous layers.
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Next: Aux Mode
Up: Shading Modes
Previous: Auto Mode
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