Geografic-Information-System/scripts/r.buffer.lowmem/r.buffer.lowmem.html

<h2>DESCRIPTION</h2>

<em>r.buffer.lowmem</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.

<p>
This is the low-memory alternative to the classic <em>r.buffer</em>
module. It is much slower than the classic version, but will
run on massive raster maps without using a lot of RAM. If your
raster map is larger than 32000x32000 cells on a system with
1 GB of RAM, or larger than 90000x90000 cells on a system with
8 GB of RAM, consider using this module.

<p>
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.

<div class="code"><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></div>
<br>

<h2>NOTES</h2>

The user has the option of identifying up to 250 continuous zones.
The zones are identified by specifying the upper limit of each desired zone
(<em>r.buffer</em> assumes that <tt>0</tt> 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 <tt>0</tt> as its lower
bound.) Buffer distances can be specified using one of five units with the <em>
units</em> parameter: <em>meters, kilometers, feet, miles</em>, and <em>nautmiles</em>
(nautical miles).
<p>
<!-- ??? is this the real method used or some ancient option ??? -->
Distances from cells containing the user-specified category values
are calculated using the "fromcell" method. This method locates 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.
<p>
<em>r.buffer</em> measures distances from center of cell to
center of cell using Euclidean distance measure for
planimetric locations (like UTM) and using ellipsoidal
geodesic distance measure for latitude/longitude locations.
<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. 
<p>
The <b>-z</b> flag can be used to ignore raster values of zero instead of NULL
values in the input raster map.
<p>
<h2>EXAMPLE</h2>

In the following example, the buffer zones would be (in the default units
of meters):  0-100, 101-200, 201-300, 301-400 and 401-500.
<br>
<div class="code"><pre>
<b>r.buffer input=</b>roads <b>output=</b>roads.buf <b>distances=</b>100,200,300,400,500
</pre></div>

Result:

<div class="code"><pre>
<b>r.category input=</b>roads.buf

      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></div>

<h2>SEE ALSO</h2>

<em>
<a href="g.region.html">g.region</a><br>
<a href="r.buffer.html">r.buffer</a><br>
<a href="r.cost.html">r.cost</a><br>
<a href="r.grow.distance.html">r.grow.distance</a><br>
<a href="r.mapcalc.html">r.mapcalc</a><br>
<a href="r.reclass.html">r.reclass</a><br>
<a href="v.buffer.html">v.buffer</a>
</em>


<h2>AUTHORS</h2>

Michael Shapiro, U.S. Army Construction Engineering 
Research Laboratory
<br>
James Westervelt, U.S. Army Construction Engineering 
Research Laboratory
<br>
Low-memory Python version by Glynn Clements

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