Geografic-Information-System/display/d.legend/d.legend.html

<h2>DESCRIPTION</h2>

<em>d.legend</em> displays a legend for a user-specified raster map or
3D raster map layer in the active frame on the graphics monitor.  
<p>
The legend's default size is based on the dimensions of the
active frame, specifically its height.  <em>d.legend</em> will only
obscure those portions of the active frame that directly underlie the legend.


<h2>NOTES</h2>

When using the <b>at</b> to size &amp; place the legend, a user may
create a horizontal legend by making the box wider than it is tall.
<p>
Raster maps based on floating point values will display smoothed, from greatest
to smallest value, while categorical raster maps will display in order, from
top to bottom. Horizontal legends will always be smoothed. If the box is defined
with inverted y-values or an inverted <b>range</b>, the legend will automatically
flip. If this is not the desired result, the <b>-f</b> flag may be used to flip
it back.
<p>
If the user attempts to display a very long legend in a relatively short 
display frame, the legend may appear in unreadably small text, or even revert
to a smooth gradient legend. Use the <b>lines</b>, <b>thin</b>, <b>use</b>, <b>range</b>,
and/or <b>-n</b> options to reduce the number of categories to be displayed,
or the <b>-s</b> flag to force a smooth gradient legend. 
<p>
The <b>lines</b> option will display the first number of categories, as defined
by <em>value</em>, contained in the raster map. When used with the <b>-n</b> flag,
it takes on a new meaning: "up to category #". When used with both
<b>thin</b> and the <b>-n</b> flag, its meaning becomes more obscure. When
using <b>lines</b>, auto-scaled text similar to "4 of 16 categories" will be placed at 
the bottom of the legend.
<p>
The <b>thin</b> option sets the thinning factor. For raster maps with a 0th
category, <b>thin=</b><em>10</em> gives cats [0,10,20,...]. For raster maps 
starting at category 1, <b>thin=</b><em>10</em> gives cats [1,11,21,...].
<p>
The <b>use</b> option lets the user create a legend made up of arbitrary category
values. e.g.&nbsp;<b>use=</b><em>1000,100,10,0,-10,-100,-1000</em>
<p>
The <b>range</b> option lets the user define the minimum and maximum categories
to be used in the legend. It may also be used to define the limits of a smooth
gradient legend created from a raster containing floating point values. Note
the color scale will remain faithful to the category values as defined with
<em><a href="r.colors.html">r.colors</a></em>, and the <b>range</b> may be
extended to the limits defined by the <em><a href="r.colors.html">r.colors</a></em>
color map.
<p>
The flag <b>-n</b> is useful for categorial maps, as it suppresses the
drawing of non-existing categories (otherwise the full range is shown).
<p>
Vertical legends produced with <em>d.legend</em> will place text labels to the
right of the legend box, horizontal legends will place text below. This text
will be auto-scaled to fit within the frame, reducing the size of the legend
if necessary. Legends positioned with the <b>at</b> option
will not auto-scale text, in order to provide more control to the user.
Smaller text may be obtained in this case by reducing the height of the box
or by using the <b>fontsize</b> option. The <b>-c</b> and <b>-v</b> flags may
be used to suppress the display of category numbers and labels respectively,
or used together to suppress all text of categorial raster maps.
<p>
The text produced from floating-point raster maps will automatically create
output with a meaningful number of significant digits. For very small values,
numbers will be expressed in scientific notation, e.g.&nbsp;"1.7e-9". Option
<b>digits</b> can be used to determine how many digits after decimal point
will be displayed.
<p>
When the <b>-d</b> flag is used to display a histogram distribution along
side the smoothed gradient legend, note that the statistics are calculated
on the <i>current computational region</i> settings set by <em>g.region</em>.
The default <b>range</b> however covers the entire natural bounds of the input map.
If the histogram appears empty, check your region settings.
<p>
If the raster map's <i>units</i> metadata has been set with the
<em>r.support</em> module then it will be displayed along side the legend.
<p>
The option <b>title</b> will display the custom title at the top of the legend. 
In case of vertical legend the title is aligned to the left edge of legend, in case
of horizontal legend the title is aligned to the center. <b>title_fontsize</b> can
be used to set the size of legend title. By default the legend title font size is
the same as labels font size. 
<p>
There are different options to customize displayed labels. The <b>labelnum</b> set
the number of labels which are displayed in regular intervals. The <b>label_values</b>
will specify the values where the labels will be displayed. The <b>label_step</b> will
display labels at values which are divisible by this value.
<p>
The flag <b>-t</b> will show ticks at labels.
<p>
The flag <b>-b</b> will show the background. Options <b>bgcolor</b> and <b>border_color</b> can be
used to choose the color of border and background fill.
<p>
The flag <b>-l</b> will switch to logarithmic scale. In case this flag is used,
the provided step in <b>label_step</b> is interpreted in the logarithmic space.
<h2>EXAMPLE</h2>

Displaying the legend along with a histogram (North Carolina Sample dataset):

<div class="code"><pre>
g.region raster=elevation -p
d.rast elevation
d.legend -d elevation
</pre></div>

<center>
<img src="d_legend.png" alt="Elevation map with legend" border=1>
</center>

Displaying the legend with custom labels and background:

<div class="code"><pre>
g.region raster=elevation -p
d.rast elevation
d.legend raster=elevation -t label_step=20 label_values=108 title=Legend -b bgcolor=255:255:204 border_color=gray
</pre></div>

<center>
<img src="d_legend_custom_labels_and_background.png" alt="Elevation map with custom legend" border=1>
</center>

Displaying the legend with logarithmic scale:

<div class="code"><pre>
g.region raster=elevation -p
r.watershed -a elevation=elevation threshold=1000 accumulation=flowacc
d.rast flowacc
d.legend raster=flowacc -t -l label_step=1
</pre></div>

<center>
<img src="d_legend_logarithmic.png" alt="Flow accumulation map with logarithmic legend" border=1>
</center>



<h2>SEE ALSO</h2>

<em>
<a href="d.barscale.html">d.barscale</a>,
<a href="d.colortable.html">d.colortable</a>,
<a href="d.font.html">d.font</a>,
<a href="d.grid.html">d.grid</a>,
<a href="d.rast.html">d.rast</a>,
<a href="d.rast.leg.html">d.rast.leg</a>,
<a href="d.text.html">d.text</a>,
<a href="d.vect.thematic.html">d.vect.thematic</a>,
<a href="r.reclass.html">r.reclass</a>,
<a href="r.stats.html">r.stats</a>,
<a href="r3.stats.html">r3.stats</a>
</em>


<h2>AUTHORS</h2>
Bill Brown, U.S. Army Construction Engineering Research Laboratories
<br>Late 2002: Rewrite of much of the code. Hamish Bowman,
 Otago University, New Zealand
<br>Additional improvements from various authors

<p>
<i>Last changed: $Date$</i>