Geografic-Information-System/raster/r.spread/r.spread.html

<h2>DESCRIPTION</h2>

Spread phenomena usually show uneven movement over space. Such unevenness
is due to two reasons:
<br>1) the uneven conditions from location to location, which can be called
SPATIAL HETEROGENEITY, and
<br>2) the uneven conditions in different directions, which can be called
ANISOTROPY.
<br>The anisotropy of spread occurs when any of the determining factors
have directional components. For example, wind and topography cause anisotropic
spread of wildfires.

<p>One of the simplest spatial heterogeneous and anisotropic spread
is elliptical spread, in which, each local spread shape can be thought
as an ellipse. In a raster setting, cell centers are foci of the spread
ellipses, and the spread phenomenon moves fastest toward apogees and slowest
to perigees. The sizes and shapes of spread ellipses may vary cell by cell.
So the overall spread shape is commonly not an ellipse.

<p><I>r.spread </I>simulates elliptically anisotropic spread phenomena,
given three raster map layers about ROS (base ROS, maximum ROS and direction
of the maximum ROS) plus a raster map layer showing the starting sources.
These ROS layers define unique ellipses for all cell locations in the current
geographic region as if each cell center was a potential spread origin.
For some wildfire spread, these ROS layers can be generated by another
GRASS raster program r.ros. The actual locations reached by a spread event
are constrained by the actual spread origins and the elapsed spread time.

<p><I>r.spread </I>optionally produces raster maps to contain backlink
UTM coordinates for each raster cell of the spread time map. The spread
paths can be accurately traced based on the backlink information by another
GRASS raster program r.spreadpath.

<p>Part of the spotting function in r.spread is based on Chase (1984)
and Rothermel (1983). More information on <I>r.spread</I>, <I><a href="r.ros.html">r.ros</a></I>
and <I><a href="r.spreadpath.html">r.spreadpath</a></I> can be found in
Xu (1994).

<h2>Flags:</h2>
<dl>

<dt>-d
<dd> Display the "live" simulation on screen. A graphics window
must be opened and selected before using this option.

<dt>-s
<dd> For wildfires, also consider spotting.
</dl>

<h2>Parameters</h2>
<dl>
 
<dt><b>max=</b>name
<dd>Name of an existing raster map layer in the user's current
mapset search path containing the maximum ROS values (cm/minute).

<dt><b>dir=</b>name 
<dd>Name of an existing raster map layer in the user's
current mapset search path containing directions of the maximum ROSes,
clockwise from north (degree).

<dt><b>base=</b>name 
<dd>Name of an existing raster map layer in the user's
current mapset search path containing the ROS values in the directions
perpendicular to maximum ROSes' (cm/minute). These ROSes are also the ones
without the effect of directional factors.

<dt><b>start=</b>name 
<dd>Name of an existing raster map layer in the
user's current mapset search path containing starting locations of the
spread phenomenon. Any positive integers in this map are recognized as
starting sources.

<dt><b>spot_dist=</b>name 
<dd>Name of an existing raster map layer in
the user's current mapset search path containing the maximum potential
spotting distances (meters).

<dt><b>w_speed=</b>name 
<dd>Name of an existing raster map layer in the
user's current mapset search path containing wind velocities at half of
the average flame height (feet/minute).

<dt><b>f_mois</b>=name 
<dd>Name of an existing raster map layer in the
user's current mapset search path containing the 1-hour (&lt;.25") fuel
moisture (percentage content multiplied by 100).

<dt><b>least_size=</b>odd int An odd integer ranging 3 - 15 indicating
the basic sampling window size within which all cells will be considered
to see whether they will be reached by the current spread cell. The default
number is 3 which means a 3x3 window.

<dt><b>comp_dens=</b>decimal A decimal number ranging 0.0 - 1.0 indicating
additional sampling cells will be considered to see whether they will be
reached by the current spread cell. The closer to 1.0 the decimal number
is, the longer the program will run and the higher the simulation accuracy
will be. The default number is 0.5.

<dt><b>init_time=</b>int A non-negative number specifying the initial
time for the current spread simulation (minutes). This is useful when multiple
phase simulation is conducted. The default time is 0.

<dt><b>lag=</b>int A non-negative integer specifying the simulating
duration time lag (minutes). The default is infinite, but the program will
terminate when the current geographic region/mask has been filled. It also
controls the computational time, the shorter the time lag, the faster the
program will run.

<dt><b>backdrop=</b>name 
<dd>Name of an existing raster map layer in the
user's current mapset search path to be used as the background on which
the "live" movement will be shown.

<dt><b>output=</b>name 
<dd>Name of the new raster map layer to contain
the results of the cumulative spread time needed for a phenomenon to reach
each cell from the starting sources (minutes).

<dt><b>x_output=</b>name 
<dd>Name of the new raster map layer to contain
the results of backlink information in UTM easting coordinates for each
cell.

<dt><b>y_output</b>=name 
<dd>Name of the new raster map layer to contain
the results of backlink information in UTM northing coordinates for each
cell.
</dl>

<h2>OPTIONS</h2>
The user can run r.spread either interactively or non- interactively. The
program is run interactively if the user types <I>r.spread</I> without
specifying flag settings and parameter values on the command line. In this
case, the user will be prompted for input.

<p>Alternately, the user can run r.spread non-interactively, by specifying
the names of raster map layers and desired options on the command line,
using the form:

<p>r.spread [-vds] max=name dir=name base=name start=name [spot_dist=name]
[w_speed=name] [f_mois=name] [least_size=odds int] [comp_dens=decimal]
[init_time=int (&gt;=0)] [lag=int (&gt;= 0)] [backdrop=name] output=name [x_output=name]
[y_output=name] The -d option can only be used after a graphics window
is opened and selected.

<p>Options spot_dist=name, w_speed=name and f_mois=name must all
be given if the -s option is used.


<h2>EXAMPLE</h2>
Assume we have inputs, the following simulates a spotting- involved wildfire
on the graphics window and generates three raster maps to contain spread
time, backlink information in UTM northing and easting coordinates:

<p>r.spread -ds max=my_ros.max dir=my_ros.maxdir base=my_ros.base
start=fire_origin spot_dist=my_ros.spotdist w_speed=wind_speed f_mois=1hour_moisture
backdrop=image_burned output=my_spread x_output=my_spread.x y_output=my_spread.y

<h2>NOTES</h2>
1. r.spread is a specific implementation of the shortest path algorithm.
r.cost GRASS program served as the starting point for the development of
r.spread. One of the major differences between the two programs is that
r.cost only simulates ISOTROPIC spread while r.spread can simulate ELLIPTICALLY
ANISOTROPIC spread, including isotropic spread as a special case.

<p>2. Before running r.spread, the user should prepare the ROS (base,
max and direction) maps using appropriate models. For some wildfire spread,
a separate GRASS program r.ros based on Rothermel's fire equation does
such work. The combination of the two forms a simulation of wildfire spread.

<p>3. The relationship of the start map and ROS maps should be logically
correct, i.e. a starting source (a positive value in the start map) should
not be located in a spread BARRIER (zero value in the ROS maps). Otherwise
the program refuses to run.

<p>4. r.spread uses the current geographic region settings. The output
map layer will not go outside the boundaries set in the region, and will
not be influenced by starting sources outside. So any change of the current
region may influence the output. The recommendation is to use slightly
larger region than needed. Refer to g.region to set an appropriate geographic
region.

<p>5. The inputs to r.spread should be in proper units.

<p>6. r.spread is a computationally intensive program. The user may
need to choose appropriate size of the geographic region and resolution.

<p>7. A low and medium (i.e. &lt;= 0.5) sampling density can improve
accuracy for elliptical simulation significantly, without adding significantly
extra running time. Further increasing the sample density will not gain
much accuracy while requiring greatly additional running time.

<h2>SEE ALSO</h2>

<em><a href="g.region.html">g.region</a></em>,
<em><a href="r.cost.html">r.cost</a></em>,
<!-- <em><a href="r.mask.html">r.mask</a></em>, -->
<em><a href="r.spreadpath.html">r.spreadpath</a></em>,
<em><a href="r.ros.html">r.ros</a></em>

<h2>REFERENCES</h2>
Chase, Carolyn, H., 1984, Spotting distance from wind-driven surface fires
-- extensions of equations for pocket calculators, US Forest Service, Res.
Note INT-346, Ogden, Utah.

<p>Rothermel, R. C., 1983, How to predict the spread and intensity
of forest and range fires. US Forest Service, Gen. Tech. Rep. INT-143.
Ogden, Utah.

<p>Xu, Jianping, 1994, Simulating the spread of wildfires using a
geographic information system and remote sensing, Ph. D. Dissertation,
Rutgers University, New Brunswick, New Jersey.

<h2>AUTHOR</h2>
Jianping Xu and Richard G. Lathrop, Jr., Center for Remote Sensing and
Spatial Analysis, Rutgers University.

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