r.spread(1grass) GRASS GIS User's Manual r.spread(1grass)
NAME
r.spread - Simulates elliptically anisotropic spread.
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. Usable for fire spread simu-
lations.
KEYWORDS
raster, fire, spread, hazard, model
SYNOPSIS
r.spread
r.spread --help
r.spread [-si] base_ros=string max_ros=string direction_ros=string
start=string [spotting_distance=string] [wind_speed=string]
[fuel_moisture=string] [least_size=odd int] [comp_dens=decimal]
[init_time=int (>= 0)] [lag=int (>= 0)] [backdrop=string] out-
put=string [x_output=string] [y_output=string] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
-s
Consider spotting effect (for wildfires)
-i
Use start raster map values in output spread time raster map
Designed to be used with output of previous run of r.spread when
computing spread iteratively. The values in start raster map are
considered as time. Allowed values in raster map are from zero to
the value of init_time option. If not enabled, init_time is used in
the area of start raster map
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
base_ros=string [required]
Raster map containing base ROS (cm/min)
Name of an existing raster map layer in the user’s current mapset
search path containing the ROS values in the directions perpendicu-
lar to maximum ROSes’ (cm/minute). These ROSes are also the ones
without the effect of directional factors.
max_ros=string [required]
Raster map containing maximal ROS (cm/min)
Name of an existing raster map layer in the user’s current mapset
search path containing the maximum ROS values (cm/minute).
direction_ros=string [required]
Raster map containing directions of maximal ROS (degree)
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).
start=string [required]
Raster map containing starting sources
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 (seeds).
spotting_distance=string
Raster map containing maximal spotting distance (m, required with
-s)
Name of an existing raster map layer in the user’s current mapset
search path containing the maximum potential spotting distances
(meters).
wind_speed=string
Raster map containing midflame wind speed (ft/min, required with
-s)
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).
fuel_moisture=string
Raster map containing fine fuel moisture of the cell receiving a
spotting firebrand (%, required with -s)
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
Basic sampling window size needed to meet certain accuracy (3)
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.
Options: 3, 5, 7, 9, 11, 13, 15
comp_dens=decimal
Sampling density for additional computing (range: 0.0 - 1.0 (0.5))
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 (>= 0)
Initial time for current simulation (0) (min)
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.
Default: 0
lag=int (>= 0)
Simulating time duration LAG (fill the region) (min)
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=string
Name of raster map as a display backdrop
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" move-
ment will be shown.
output=string [required]
Raster map to contain output spread time (min)
Name of the new raster map layer to contain the results of the cu-
mulative spread time needed for a phenomenon to reach each cell
from the starting sources (minutes).
x_output=string
Name of raster map to contain X back coordinates
Name of the new raster map layer to contain the results of backlink
information in UTM easting coordinates for each cell.
y_output=string
Name of raster map to contain Y back coordinates
Name of the new raster map layer to contain the results of backlink
information in UTM northing coordinates for each cell.
DESCRIPTION
r.spread is part of the wildfire simulation toolset. Preparational
steps for the fire simulation are the calculation of the rate of spread
(ROS) with r.ros, and the creating of spread map with r.spread. Even-
tually, the fire path(s) based on starting point(s) are calculated with
r.spreadpath.
Spread phenomena usually show uneven movement over space. Such uneven-
ness 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 an-
isotropic spread of wildfires.
One of the simplest spatial heterogeneous and anisotropic spread is el-
liptical spread, in which, each local spread shape can be thought as an
ellipse. In a raster setting, cell centers are foci of the spread el-
lipses, 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.spreadsimulates 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 loca-
tions in the current computational 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 lo-
cations reached by a spread event are constrained by the actual spread
origins and the elapsed spread time.
r.spreadoptionally produces raster maps to contain backlink UTM coordi-
nates for each raster cell of the spread time map. The spread paths can
be accurately traced based on the backlink information by r.spreadpath
module.
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).
Options spot_dist, w_speed and f_mois must all be given if the -s
(spotting) flag is used.
EXAMPLE
Assume we have inputs, the following simulates a spotting- involved
wildfire and generates three raster maps to contain spread time, back-
link information in UTM northing and easting coordinates:
r.spread -s 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 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 algo-
rithm. r.cost module 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 spe-
cial case.
2. Before running r.spread, the user should prepare the ROS (base, max
and direction) maps using appropriate models. For some wildfire spread,
the r.ros module 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 computational 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 computational region.
5. The user should be sure that the inputs to r.spread are in proper
units.
6. r.spread is a computationally intensive program. The user may need
to choose appropriate size of the computational 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.
REFERENCES
• Chase, Carolyn, H., 1984, Spotting distance from wind-driven
surface fires -- extensions of equations for pocket calcula-
tors, 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. Dis-
sertation, Rutgers University, New Brunswick, New Jersey (ref).
SEE ALSO
r.cost, r.mask, r.ros, r.spreadpath Sample data download: firedemo.sh
(run this script within the "Fire simulation data set" location.
AUTHOR
Jianping Xu and Richard G. Lathrop, Jr., Center for Remote Sensing and
Spatial Analysis, Rutgers University.
SOURCE CODE
Available at: r.spread source code (history)
Accessed: unknown
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GRASS 7.8.7 r.spread(1grass)
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