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<H2>DESCRIPTION</H2>
<EM>r.buffer</EM> creates a new raster map layer showing
buffer (a.k.a. "distance" or "proximity") zones around all
cells that contain non-NULL category values in an existing
raster map layer. The distances of buffer zones from cells
with non-zero category values are user-chosen. Suppose,
for example, that you want to place buffer zones around
roads. This program could create the raster map layer
shown below on the right based on road information
contained in the raster map layer shown on the left.
<PRE>
000000000000000000000000 222233333333333333444444
111000000000000000000000 111222222222223333333333
000111111111100000000000 222111111111122223333333
000000001000011100000000 332222221222211122222222
000000001000000011111111 333333321233222211111111
000000001000000000000000 433333321233333222222222
000000001000000000000000 444443321233333333333333
000000001000000000000000 444443321233443333333333
000000001000000000000000 444443321233444444444444
Category 0: No roads
Category 1: Road location
Category 2: Buffer Zone 1 around roads
Category 3: Buffer Zone 2 around roads
Category 4: Buffer Zone 3 around roads
</PRE>
<H2>INTERACTIVE PROGRAM USE</H2>
The user can run the program interactively by simply typing
<B>r.buffer</B> without program arguments on the command
line. The program then prompts the user for parameter
values.
<OL>
<LI>You are requested to identify the existing raster map
layer from which distance-from calculations shall be based,
and a name (of your choice) for the new raster map layer
which will contain the results.
<LI>Then, identify the units of measurement in which buffer
(distance) zones are to be calculated, and the distance of
each buffer zone from each non-NULL cell in the
<EM>input</EM> map. The user has the option of identifying
up to 60 continuous zones. The zones are identified by
specifying the upper limit of each desired zone
(<EM>r.buffer</EM> assumes that 0 is the starting point).
("Continuous" is used in the sense that each category
zone's lower value is the previous zone's upper value. The
first buffer zone always has distance 0 as its lower
bound.) Distances can be entered in one of five units:
<EM>meters, kilometers, feet, miles</EM>, and <EM>nautmiles</EM>
(nautical miles).
<LI>Last, calculate distances from cells containing
user-specified category values, using the "fromcell"
method. [The "fromcell" method goes to each cell that
contains a category value from which distances are to be
calculated, and draws the requested distance rings around
them. This method works very fast when there are few cells
containing the category values of interest, but works
slowly when there are numerous cells containing the
category values of interest spread throughout the area.]
</OL>
<H2>NON-INTERACTIVE PROGRAM USE</H2>
The user can run <EM>r.buffer</EM> specifying all parameter
values on the command line (see above).
<H2>EXAMPLE</H2>
In the example below, the buffer zones would be (in the
default units of meters): 0-100, 101-200, 201-300, 301-400 and
401-500.
<DL>
<DT> Format:
<DD>
<B>r.buffer</B>
[<B>-q</B>]
<B>input=</B><EM>name</EM>
<B>output=</B><EM>name</EM>
<B>distances=</B><EM>value</EM>[,<EM>value</EM>,...]
<DT> Example:
<DD>
<B>r.buffer input=</B>roads <B>output=</B>roads.buf
<B>distances=</B>100,200,300,400,500
<B>units=</B>meters
</DL>
<DT> Result:
<DD>
<B>r.cats input=</B>roads.buf
<pre>
1 distances calculated from these locations
2 0-100 meters
3 100-200 meters
4 200-300 meters
5 300-400 meters
6 400-500 meters
</pre>
<H2>NOTES</H2>
<EM>r.buffer</EM> measures distances from center of cell to
center of cell using Euclidean distance measure for
planimetric databases (like UTM) and using ellipsoidal
geodesic distance measure for latitude/longitude
databases.
<P>
<EM>r.buffer</EM> calculates distance zones from all cells having non-NULL
category values in the <EM>input</EM> map.
If the user wishes to calculate distances from only selected <EM>input</EM> map layer
category values, the user should run (for example)
<EM><A HREF="r.reclass.html">r.reclass</A></EM> prior to
<EM>r.buffer</EM>, to reclass all categories from which distance zones
are not desired to be calculated into category NULL.
<H2>SEE ALSO</H2>
<EM><A HREF="g.region.html">g.region</A></EM><br>
<EM><A HREF="r.mapcalc.html">r.mapcalc</A></EM><br>
<EM><A HREF="r.reclass.html">r.reclass</A></EM>
<H2>AUTHORS</H2>
Michael Shapiro, U.S. Army Construction Engineering
Research Laboratory
<BR>
James Westervelt, U.S. Army Construction Engineering
Research Laboratory
<p><i>Last changed: $Date: 2004/05/25 13:03:03 $</i>
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