1r.spread(1)                 GRASS GIS User's Manual                r.spread(1)
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NAME

6       r.spread  - Simulates elliptically anisotropic spread.
7       Generates  a  raster map of the cumulative time of spread, given raster
8       maps containing the rates of spread (ROS), the ROS directions  and  the
9       spread  origins. It optionally produces raster maps to contain backlink
10       UTM coordinates for tracing spread paths. Usable for fire spread  simu‐
11       lations.
12

KEYWORDS

14       raster, fire, spread, hazard, model
15

SYNOPSIS

17       r.spread
18       r.spread --help
19       r.spread   [-si]  base_ros=string  max_ros=string  direction_ros=string
20       start=string      [spotting_distance=string]        [wind_speed=string]
21       [fuel_moisture=string]     [least_size=odd  int]    [comp_dens=decimal]
22       [init_time=int (>= 0)]   [lag=int  (>=  0)]    [backdrop=string]   out‐
23       put=string    [x_output=string]     [y_output=string]     [--overwrite]
24       [--help]  [--verbose]  [--quiet]  [--ui]
25
26   Flags:
27       -s
28           Consider spotting effect (for wildfires)
29
30       -i
31           Use start raster map values in output spread time raster map
32           Designed to be used with output of previous run  of  r.spread  when
33           computing  spread  iteratively.  The values in start raster map are
34           considered as time. Allowed values in raster map are from  zero  to
35           the value of init_time option. If not enabled, init_time is used in
36           the area of start raster map
37
38       --overwrite
39           Allow output files to overwrite existing files
40
41       --help
42           Print usage summary
43
44       --verbose
45           Verbose module output
46
47       --quiet
48           Quiet module output
49
50       --ui
51           Force launching GUI dialog
52
53   Parameters:
54       base_ros=string [required]
55           Raster map containing base ROS (cm/min)
56           Name of an existing raster map layer in the user’s  current  mapset
57           search path containing the ROS values in the directions perpendicu‐
58           lar to maximum ROSes’ (cm/minute). These ROSes are  also  the  ones
59           without the effect of directional factors.
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61       max_ros=string [required]
62           Raster map containing maximal ROS (cm/min)
63           Name  of  an existing raster map layer in the user’s current mapset
64           search path containing the maximum ROS values (cm/minute).
65
66       direction_ros=string [required]
67           Raster map containing directions of maximal ROS (degree)
68           Name of an existing raster map layer in the user’s  current  mapset
69           search  path  containing directions of the maximum ROSes, clockwise
70           from north (degree).
71
72       start=string [required]
73           Raster map containing starting sources
74           Name of an existing raster map layer in the user’s  current  mapset
75           search path containing starting locations of the spread phenomenon.
76           Any positive integers  in  this  map  are  recognized  as  starting
77           sources (seeds).
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79       spotting_distance=string
80           Raster  map  containing maximal spotting distance (m, required with
81           -s)
82           Name of an existing raster map layer in the user’s  current  mapset
83           search  path  containing  the  maximum potential spotting distances
84           (meters).
85
86       wind_speed=string
87           Raster map containing midflame wind speed  (ft/min,  required  with
88           -s)
89           Name  of  an existing raster map layer in the user’s current mapset
90           search path containing wind velocities at half of the average flame
91           height (feet/minute).
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93       fuel_moisture=string
94           Raster  map  containing  fine fuel moisture of the cell receiving a
95           spotting firebrand (%, required with -s)
96           Name of an existing raster map layer in the user’s  current  mapset
97           search path containing the 1-hour (<.25") fuel moisture (percentage
98           content multiplied by 100).
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100       least_size=odd int
101           Basic sampling window size needed to meet certain accuracy (3)
102           An odd integer ranging 3 - 15 indicating the basic sampling  window
103           size  within which all cells will be considered to see whether they
104           will be reached by the current spread cell. The default number is 3
105           which means a 3x3 window.
106           Options: 3, 5, 7, 9, 11, 13, 15
107
108       comp_dens=decimal
109           Sampling density for additional computing (range: 0.0 - 1.0 (0.5))
110           A  decimal  number ranging 0.0 - 1.0 indicating additional sampling
111           cells will be considered to see whether they will be reached by the
112           current  spread  cell. The closer to 1.0 the decimal number is, the
113           longer the program will run and the higher the simulation  accuracy
114           will be. The default number is 0.5.
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116       init_time=int (>= 0)
117           Initial time for current simulation (0) (min)
118           A  non-negative  number specifying the initial time for the current
119           spread simulation (minutes). This is  useful  when  multiple  phase
120           simulation is conducted. The default time is 0.
121           Default: 0
122
123       lag=int (>= 0)
124           Simulating time duration LAG (fill the region) (min)
125           A  non-negative integer specifying the simulating duration time lag
126           (minutes). The default is infinite, but the program will  terminate
127           when  the  current  geographic region/mask has been filled. It also
128           controls the computational time, the  shorter  the  time  lag,  the
129           faster the program will run.
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131       backdrop=string
132           Name of raster map as a display backdrop
133           Name  of  an existing raster map layer in the user’s current mapset
134           search path to be used as the background on which the "live"  move‐
135           ment will be shown.
136
137       output=string [required]
138           Raster map to contain output spread time (min)
139           Name  of  the  new  raster  map layer to contain the results of the
140           cumulative spread time needed for a phenomenon to reach  each  cell
141           from the starting sources (minutes).
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143       x_output=string
144           Name of raster map to contain X back coordinates
145           Name of the new raster map layer to contain the results of backlink
146           information in UTM easting coordinates for each cell.
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148       y_output=string
149           Name of raster map to contain Y back coordinates
150           Name of the new raster map layer to contain the results of backlink
151           information in UTM northing coordinates for each cell.
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DESCRIPTION

154       r.spread  is  part  of  the  wildfire simulation toolset. Preparational
155       steps for the fire simulation are the calculation of the rate of spread
156       (ROS)  with r.ros, and the creating of spread map with r.spread.  Even‐
157       tually, the fire path(s) based on starting point(s) are calculated with
158       r.spreadpath.
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160       Spread  phenomena usually show uneven movement over space. Such uneven‐
161       ness is due to two reasons:
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163       1      the uneven conditions from location to location,  which  can  be
164              called spatial heterogeneity, and
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166       2      the  uneven  conditions  in  different  directions, which can be
167              called anisotropy.
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169       The anisotropy of spread occurs when any  of  the  determining  factors
170       have directional components. For example, wind and topography cause an‐
171       isotropic spread of wildfires.
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173       One of the simplest spatial heterogeneous  and  anisotropic  spread  is
174       elliptical  spread, in which, each local spread shape can be thought as
175       an ellipse. In a raster setting, cell centers are foci  of  the  spread
176       ellipses,  and  the  spread phenomenon moves fastest toward apogees and
177       slowest to perigees. The sizes and shapes of spread ellipses  may  vary
178       cell by cell.  So the overall spread shape is commonly not an ellipse.
179
180       r.spreadsimulates  elliptically  anisotropic  spread  phenomena,  given
181       three raster map layers about ROS (base ROS, maximum ROS and  direction
182       of  the  maximum  ROS)  plus  a  raster  map layer showing the starting
183       sources.  These ROS layers define unique ellipses for  all  cell  loca‐
184       tions  in the current computational region as if each cell center was a
185       potential spread origin.  For some wildfire spread,  these  ROS  layers
186       can  be  generated  by  another  GRASS raster program r.ros. The actual
187       locations reached by a spread  event  are  constrained  by  the  actual
188       spread origins and the elapsed spread time.
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190       r.spreadoptionally produces raster maps to contain backlink UTM coordi‐
191       nates for each raster cell of the spread time map. The spread paths can
192       be  accurately traced based on the backlink information by r.spreadpath
193       module.
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195       Part of the spotting function in r.spread is based on Chase (1984)  and
196       Rothermel  (1983). More information on r.spread, r.ros and r.spreadpath
197       can be found in Xu (1994).
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199       Options spot_dist, w_speed and f_mois must  all  be  given  if  the  -s
200       (spotting) flag is used.
201

EXAMPLE

203       Assume  we  have  inputs,  the following simulates a spotting- involved
204       wildfire and generates three raster maps to contain spread time,  back‐
205       link information in UTM northing and easting coordinates:
206       r.spread -s max=my_ros.max dir=my_ros.maxdir base=my_ros.base \
207           start=fire_origin spot_dist=my_ros.spotdist w_speed=wind_speed \
208           f_mois=1hour_moisture output=my_spread \
209           x_output=my_spread.x y_output=my_spread.y
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NOTES

212       1.  r.spread  is  a  specific implementation of the shortest path algo‐
213       rithm. r.cost module served as the starting point for  the  development
214       of  r.spread.  One of the major differences between the two programs is
215       that r.cost only simulates isotropic spread while r.spread can simulate
216       elliptically  anisotropic  spread, including isotropic spread as a spe‐
217       cial case.
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219       2. Before running r.spread, the user should prepare the ROS (base,  max
220       and direction) maps using appropriate models. For some wildfire spread,
221       the r.ros module based on Rothermel’s fire  equation  does  such  work.
222       The combination of the two forms a simulation of wildfire spread.
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224       3.  The  relationship of the start map and ROS maps should be logically
225       correct, i.e. a starting source (a positive value  in  the  start  map)
226       should not be located in a spread barrier (zero value in the ROS maps).
227       Otherwise the program refuses to run.
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229       4. r.spread uses the current computational region settings. The  output
230       map  layer  will  not  go outside the boundaries set in the region, and
231       will not be influenced by starting sources outside. So  any  change  of
232       the  current  region may influence the output. The recommendation is to
233       use slightly larger region than needed.  Refer to g.region  to  set  an
234       appropriate computational region.
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236       5.  The  user  should be sure that the inputs to r.spread are in proper
237       units.
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239       6. r.spread is a computationally intensive program. The user  may  need
240       to choose appropriate size of the computational region and resolution.
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242       7. A low and medium (i.e. <= 0.5) sampling density can improve accuracy
243       for elliptical simulation significantly, without  adding  significantly
244       extra running time. Further increasing the sample density will not gain
245       much accuracy while requiring greatly additional running time.
246

REFERENCES

248           ·   Chase, Carolyn, H., 1984, Spotting  distance  from  wind-driven
249               surface  fires  --  extensions of equations for pocket calcula‐
250               tors, US Forest Service, Res.  Note INT-346, Ogden, Utah.
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252           ·   Rothermel, R. C., 1983, How to predict the spread and intensity
253               of  forest  and range fires. US Forest Service, Gen. Tech. Rep.
254               INT-143.  Ogden, Utah.
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256           ·   Xu, Jianping, 1994, Simulating the spread of wildfires using  a
257               geographic  information  system and remote sensing, Ph. D. Dis‐
258               sertation, Rutgers University, New Brunswick, New Jersey (ref).
259

SEE ALSO

261        r.cost, r.mask, r.ros, r.spreadpath Sample data download:  firedemo.sh
262       (run this script within the "Fire simulation data set" location.
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AUTHOR

265       Jianping  Xu and Richard G. Lathrop, Jr., Center for Remote Sensing and
266       Spatial Analysis, Rutgers University.
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SOURCE CODE

269       Available at: r.spread source code (history)
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271       Main index | Raster index | Topics index | Keywords index  |  Graphical
272       index | Full index
273
274       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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278GRASS 7.8.5                                                        r.spread(1)
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