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NAME
r.spread - Simulates elliptically anisotropic spread on a graphics window and generates a raster map of
the cumulative time of spread, given raster maps containing the rates of spread (ROS), the ROS directions
and the spread origins.
It optionally produces raster maps to contain backlink UTM coordinates for tracing spread paths.
KEYWORDS
raster, fire
SYNOPSIS
r.spread
r.spread help
r.spread [-vds] max=string dir=string base=string start=string [spot_dist=string] [w_speed=string]
[f_mois=string] [least_size=odd int] [comp_dens=decimal] [init_time=int (>= 0)] [lag=int (>= 0)]
[backdrop=string] output=string [x_output=string] [y_output=string] [--overwrite] [--verbose]
[--quiet]
Flags:
-v
Run VERBOSELY
-d
DISPLAY 'live' spread process on screen
-s
For wildfires: consider SPOTTING effect
--overwrite
Allow output files to overwrite existing files
--verbose
Verbose module output
--quiet
Quiet module output
Parameters:
max=string
Name of raster map containing MAX rate of spread (ROS) (cm/min)
dir=string
Name of raster map containing DIRections of max ROS (degree)
base=string
Name of raster map containing BASE ROS (cm/min)
start=string
Name of raster map containing STARTing sources
spot_dist=string
Name of raster map containing max SPOTting DISTance (m) (required w/ -s)
w_speed=string
Name of raster map containing midflame Wind SPEED (ft/min) (required w/ -s)
f_mois=string
Name of raster map containing fine Fuel MOISture of the cell receiving a spotting firebrand (%)
(required w/ -s)
least_size=odd int
Basic sampling window SIZE needed to meet certain accuracy (3)
Options: 3,5,7,9,11,13,15
comp_dens=decimal
Sampling DENSity for additional COMPutin (range: 0.0 - 1.0 (0.5))
init_time=int (>= 0)
INITial TIME for current simulation (0) (min)
lag=int (>= 0)
Simulating time duration LAG (fill the region) (min)
backdrop=string
Name of raster map as a display backdrop
output=string
Name of raster map to contain OUTPUT spread time (min)
x_output=string
Name of raster map to contain X_BACK coordinates
y_output=string
Name of raster map to contain Y_BACK coordinates
DESCRIPTION
Spread phenomena usually show uneven movement over space. Such unevenness is due to two reasons:
1) the uneven conditions from location to location, which can be called SPATIAL HETEROGENEITY, and
2) the uneven conditions in different directions, which can be called ANISOTROPY.
The anisotropy of spread occurs when any of the determining factors have directional components. For
example, wind and topography cause anisotropic spread of wildfires.
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.
r.spread 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.
r.spread 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.
Part of the spotting function in r.spread is based on Chase (1984) and Rothermel (1983). More information
on r.spread, r.ros and r.spreadpath can be found in Xu (1994).
Flags:
-v
Run verbosely, printing information about program progress to standard output.
-d
Display the "live" simulation on screen. A graphics window must be opened and selected before
using this option.
-s
For wildfires, also consider spotting.
Parameters
max=name
Name of an existing raster map layer in the user's current mapset search path containing the
maximum ROS values (cm/minute).
dir=name
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).
base=name
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.
start=name
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.
spot_dist=name
Name of an existing raster map layer in the user's current mapset search path containing the
maximum potential spotting distances (meters).
w_speed=name
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).
f_mois=name
Name of an existing raster map layer in the user's current mapset search path containing the
1-hour (<.25") fuel moisture (percentage content multiplied by 100).
least_size=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.
comp_dens=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.
init_time=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.
lag=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.
backdrop=name
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.
output=name
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).
x_output=name
Name of the new raster map layer to contain the results of backlink information in UTM easting
coordinates for each cell.
y_output=name
Name of the new raster map layer to contain the results of backlink information in UTM northing
coordinates for each cell.
OPTIONS
The user can run r.spread either interactively or non- interactively. The program is run interactively if
the user types r.spread without specifying flag settings and parameter values on the command line. In
this case, the user will be prompted for input.
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:
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 (>=0)] [lag=int (>= 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.
Options spot_dist=name, w_speed=name and f_mois=name must all be given if the -s option is used.
EXAMPLE
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:
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
NOTES
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.
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.
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.
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.
5. The inputs to r.spread should be in proper units.
6. r.spread is a computationally intensive program. The user may need to choose appropriate size of the
geographic region and resolution.
7. A low and medium (i.e. <= 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.
SEE ALSO
g.region, r.cost, r.spreadpath, r.ros
REFERENCES
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.
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.
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.
AUTHOR
Jianping Xu and Richard G. Lathrop, Jr., Center for Remote Sensing and Spatial Analysis, Rutgers
University.
Last changed: $Date: 2006-04-13 12:25:42 -0700 (Thu, 13 Apr 2006) $
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