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<h4><a name="shading-density">8.4.5 <code>density</code></a></h4>
<p>Paints markers using 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 markers
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
markers plotted by the layer.
The upshot is that you can see the plot density
of points or other markers plotted.
</p>
<p>This is like <a href="shading-auto.html">auto</a> mode,
but with more user-configurable options.
</p>
<p>
<strong>Usage:</strong>
<pre>
shadingN=density colorN=<rrggbb>|red|blue|...
densemapN=<map-name>|<color>-<color>[-<color>...]
denseclipN=<lo>,<hi> denseflipN=true|false
densequantN=<number> densefuncN=log|linear|sqrt|square
densesubN=<lo>,<hi>
</pre>
</p>
<p>All the parameters listed here
affect only the relevant layer,
identified by the suffix
<code>N</code>.
</p>
<p>
<strong>Example:</strong>
</p>
<div align="center"><img src="plot2-shading-density.png" alt="" align="middle"></div>
<p><pre> stilts plot2plane layer1=mark in1=dr5qso.fits
<strong>shading1=density</strong> <strong>densemap1=viridis</strong>
x1=psfmag_g-psfmag_r y1=psfmag_u-psfmag_g size1=2
xmin=-0.5 xmax=2.5 ymin=-1 ymax=6</pre></p>
<p>Associated parameters are as follows:
<dl>
<dt><strong><code>colorN = <rrggbb>|red|blue|...</code> <em>(<a href="http://docs.oracle.com/javase/6/docs/api/java/awt/Color.html">Color</a>)</em></strong></dt>
<dd>The color of plotted data,
given by name or as a hexadecimal RGB value.
<p>The standard plotting colour names are
<code>red</code>, <code>blue</code>, <code>green</code>, <code>grey</code>, <code>magenta</code>, <code>cyan</code>, <code>orange</code>, <code>pink</code>, <code>yellow</code>, <code>black</code>, <code>light_grey</code>, <code>white</code>.
However, many other common colour names (too many to list here)
are also understood.
The list currently contains those colour names understood
by most web browsers,
from <code>AliceBlue</code> to <code>YellowGreen</code>,
listed e.g. in the
<em>Extended color keywords</em> section of
the <a href="http://www.w3c.org/TR/css3-color#svg-color">CSS3</a> standard.
</p>
<p>Alternatively, a six-digit hexadecimal number <em>RRGGBB</em>
may be supplied,
optionally prefixed by "<code>#</code>" or "<code>0x</code>",
giving red, green and blue intensities,
e.g. "<code>ff00ff</code>", "<code>#ff00ff</code>"
or "<code>0xff00ff</code>" for magenta.
</p>
<p>[Default: <code>red</code>]
</p>
</dd>
<dt><strong><code>denseclipN = <lo>,<hi></code> <em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot2/Subrange.html">Subrange</a>)</em></strong></dt>
<dd>Defines a subrange of the colour ramp to be used for
Density shading.
The value is specified as a (low,high) comma-separated pair
of two numbers between 0 and 1.
<p>If the full range <code>0,1</code> is used,
the whole range of colours specified by the selected
shader will be used.
But if for instance a value of <code>0,0.5</code> is given,
only those colours at the left hand end of the ramp
will be seen.
</p>
<p>If the null (default) value is chosen,
a default clip will be used.
This generally covers most or all of the range 0-1
but for colour maps which fade to white,
a small proportion of the lower end may be excluded,
to ensure that all the colours are visually distinguishable
from a white background.
This default is usually a good idea if the colour map
is being used with something like a scatter plot,
where markers are plotted against a white background.
However, for something like a density map when the whole
plotting area is tiled with colours from the map,
it may be better to supply the whole range
<code>0,1</code> explicitly.
</p>
</dd>
<dt><strong><code>denseflipN = true|false</code> <em>(Boolean)</em></strong></dt>
<dd>If true, the colour map on the
Density
axis will be reversed.
<p>[Default: <code>false</code>]
</p>
</dd>
<dt><strong><code>densefuncN = log|linear|sqrt|square</code> <em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot2/Scaling.html">Scaling</a>)</em></strong></dt>
<dd>Defines the way that values in the
Density
range are mapped to the selected colour ramp.
<p>The available options are:
<ul>
<li><code>log</code>: Logarithmic scaling
</li>
<li><code>linear</code>: Linear scaling
</li>
<li><code>sqrt</code>: Square root scaling
</li>
<li><code>square</code>: Square scaling
</li>
</ul>
</p>
<p>[Default: <code>log</code>]
</p>
</dd>
<dt><strong><code>densemapN = <map-name>|<color>-<color>[-<color>...]</code> <em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot/Shader.html">Shader</a>)</em></strong></dt>
<dd>Color map used for
Density
axis shading.
<p>A mixed bag of colour ramps are available:
<code>blacker</code>,
<code>whiter</code>,
<code>inferno</code>,
<code>magma</code>,
<code>plasma</code>,
<code>viridis</code>,
<code>cubehelix</code>,
<code>sron</code>,
<code>rainbow</code>,
<code>rainbow2</code>,
<code>rainbow3</code>,
<code>pastel</code>,
<code>accent</code>,
<code>gnuplot</code>,
<code>gnuplot2</code>,
<code>specxby</code>,
<code>set1</code>,
<code>paired</code>,
<code>hotcold</code>,
<code>rdbu</code>,
<code>piyg</code>,
<code>brbg</code>,
<code>cyan-magenta</code>,
<code>red-blue</code>,
<code>brg</code>,
<code>heat</code>,
<code>cold</code>,
<code>light</code>,
<code>greyscale</code>,
<code>colour</code>,
<code>standard</code>,
<code>bugn</code>,
<code>bupu</code>,
<code>orrd</code>,
<code>pubu</code>,
<code>purd</code>,
<code>huecl</code>,
<code>hue</code>,
<code>intensity</code>,
<code>rgb_red</code>,
<code>rgb_green</code>,
<code>rgb_blue</code>,
<code>hsv_h</code>,
<code>hsv_s</code>,
<code>hsv_v</code>,
<code>yuv_y</code>,
<code>yuv_u</code>,
<code>yuv_v</code>,
<code>scale_hsv_s</code>,
<code>scale_hsv_v</code>,
<code>scale_yuv_y</code>.
<em>Note:</em>
many of these, including rainbow-like ones,
are frowned upon by the visualisation community.
</p>
<p>You can also construct your own custom colour map
by giving a sequence of colour names separated by
minus sign ("<code>-</code>") characters.
In this case the ramp is a linear interpolation
between each pair of colours named,
using the same syntax as when specifying
a colour value.
So for instance
"<code>yellow-hotpink-#0000ff</code>"
would shade from yellow via hot pink to blue.
</p>
<p>[Default: <code>blacker</code>]
</p>
</dd>
<dt><strong><code>densequantN = <number></code> <em>(Double)</em></strong></dt>
<dd>Allows the colour map used for the
Density
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.
<p>If left blank, the colour map is
nominally continuous (though in practice it may be quantised
to a medium-sized number like 256).
</p>
</dd>
<dt><strong><code>densesubN = <lo>,<hi></code> <em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot2/Subrange.html">Subrange</a>)</em></strong></dt>
<dd>Defines a normalised adjustment to the data range of the
Density 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.
<p>The default value "<code>0,1</code>" therefore has
no effect.
The range could be restricted to its lower half
with the value <code>0,0.5</code>.
</p>
<p>[Default: <code>0,1</code>]
</p>
</dd>
</dl>
</p>
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<hr><i>STILTS - Starlink Tables Infrastructure Library Tool Set<br>Starlink User Note256<br>STILTS web page:
<a href="http://www.starlink.ac.uk/stilts/">http://www.starlink.ac.uk/stilts/</a><br>Author email:
<a href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a><br>Mailing list:
<a href="mailto:topcat-user@jiscmail.ac.uk">topcat-user@jiscmail.ac.uk</a><br></i></body>
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