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

<h2>DESCRIPTION</h2>

<em>d.linegraph</em> is a module to draw simple x,y line graphs
(plots) based on numerical data contained in separate files.


<h3>Data format</h3>

The X and Y data files for the graph are essentially a column of numbers in
each file, with one input number per line.  The program expects that each X
value will have a corresponding Y value, therefore the number of lines in
each data input file should be the same.  Essentially, the X data becomes
the X axis reference to which the Y data is plotted as a line. Therefore,
the X data should be a monotonically increasing progression of numbers (i.e.
"1,2,3,..."; "0, 10, 100, 1000,..."; "...-5,-1,0,1,5...").  If multiple Y
data files are used, the Y axis scale will be based on the range of minimum
and maximum values from all Y files, then all Y data given will be graphed
according to that Y scale. Therefore, if multiple Y data inputs are used
with dissimilar units, the graph produced comparing the two will be
deceptive.


<h3>File inputs</h3>

If the <b>directory</b> option is provided, the paths to files can (and
should) be only relative paths to these files. While this is not recommended
for scripting, it can be advantageous when typing the paths
manually. For example when all files are stored in the directory
<tt>/home/john/data</tt>, the user can provide the following in the command
line:

<div class="code"><pre>
d.linegraph directory=/home/john/data x_file=x.txt y_file=y1.txt,y2.txt
</pre></div>


<h3>Managing colors</h3>

The user can specify the <b>y_color</b> option, the <b>color_table</b>
option or just leave the defaults to influence the color of the
plotted lines.

<p>
Colors specified by <b>y_color</b> option are used for drawing the lines
in the graph. If multiple Y data files are used, an equal number of
colors may be used to control the colors of the lines. Colors will be
assigned to Y data in respect to the sequence of instantiation on the
command line. It can be one of GRASS GIS named colors or the RGB
values from 0-255 separated by colons (RRR:GGG:BBB).

<p>
Alternatively, the user can use the <b>color_table</b> option to specify one
of the GRASS GIS predefined color tables.

<p>
By default, a series of colors will be chosen by the module if none are
provided upon invocation. The order of default colors is red, green,
violet, blue, orange, gray, brown, magenta, white, and indigo. The user is
advised not to rely on the order of default colors but to either use the
<b>y_color</b> or the <b>color_table</b> option to obtain predictable and
reproducible results.

<p>
The color to be used for titles, axis lines, tics, and scale numbers
is determined by the <b>title_color</b> option. The user can provide
one of the GRASS GIS named colors (such as gray, white, or black)
or use the GRASS GIS colon-separated format for RGB (RRR:GGG:BBB).

<h3>Titles, labels, and tics</h3>

The <b>title</b> option specifies the text for the title of the graph.
It will be centered over the top of graph.

The <b>x_title</b> option is a text to describe data for X axis. It will be
centered beneath the graph. Default is no text unless there is a need
for a unit descriptor determined by the <em>d.linegraph</em> module,
then string such as "in hundreds" is generated.

The <b>y_title</b> option is a text to describe data for Y axis. It
will be centered beneath the X data description. Similarly, to the
<b>x_title</b> option, default is no text unless there is a need for an
auto-generated description. In the case of graphs with multiple lines
(multiple inputs for Y axis), user may wish to use more specific text
placement using the <em><a href="d.text.html">d.text</a></em> or
<em><a href="v.label.html">v.label</a></em> programs.


<h2>NOTES</h2>

For historical reasons, the <em>d.linegraph</em> module accepts
titles of more than one word where the underscore character ("_")
is used to represent spaces (" "). For example "Census_data_1990" would be
printed over the graph as "Census data 1990". The use of underscores is not
necessary to use as long as the parameter is quoted in the command line.
In general, use of underscores is not recommended and there is no need to use
it at all in the GUI or when using <em>d.linegraph</em> in Python scripts.

<p>
The way the program locates and labels tic marks is less than perfect:
<br>
1) although distances between Y tics are proportional to the value, they are
not proportional on the X axis;
<br>
2) decimal values between -1 and 1 can be printed on the X axis, but not
on Y. (With respect to the later, the input for Y values can all be
multiplied by a factor of 10 before graphing).

<p>
Depending on the user's needs, it might be easier or more appropriate
to use a 3rd party tool such as xgraph, gnuplot, Matplotlib in Python,
or R instead of <em>d.linegraph</em>.
For a more general solution for plotting in GRASS GIS, the user is
advised to use the <em><a href="d.graph.html">d.graph</a></em> module.


<h2>EXAMPLE</h2>

The following can be executed in Bash to create the input data for this
example. The user can just create these files in a text editor, save
them and specify path to them.

<div class="code"><pre>
cat &gt; x.txt &lt;&lt;EOF
1
3
4
6
9
EOF
cat &gt; y1.txt &lt;&lt;EOF
50
58
65
34
27
EOF
cat &gt; y2.txt &lt;&lt;EOF
10
20
35
50
45
EOF
</pre></div>

<!--
export GRASS_FONT=sans  # fixes bad default font
d.mon start=cairo output=plot.png width=400 height=400
d.erase  # previous image is not cleaned
-->

<p>
The next command sequence creates a file <tt>plot.png</tt> in the current
directory which is the drawing made by <em>d.linegraph</em>.

<div class="code"><pre>
d.mon start=cairo output=plot.png width=400 height=400
d.linegraph x_file=x.txt y_file=y1.txt,y2.txt
d.mon stop=cairo
</pre></div>


<h2>SEE ALSO</h2>
<em>
<a href="d.frame.html">d.frame</a>,
<a href="d.text.html">d.text</a>,
<a href="v.label.html">v.label</a>,
<a href="d.graph.html">d.graph</a>,
<a href="d.histogram.html">d.histogram</a>
</em>


<h2>AUTHOR</h2>
Chris Rewerts, Agricultural Engineering, Purdue University

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