Provided by: grass-doc_7.6.1-3build1_all bug

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 simulations.

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]   output=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  perpendicular  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" movement 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 cumulative 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.   Eventually, the fire path(s) based on starting point(s) are
       calculated with r.spreadpath.

       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.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
       locations 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 locations 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 coordinates 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, backlink 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  algorithm.  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
       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, 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 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 (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.

       Last changed: $Date: 2014-10-27 16:35:33 +0100 (Mon, 27 Oct 2014) $

SOURCE CODE

       Available at: r.spread source code (history)

       Main index | Raster index | Topics index | Keywords index | Graphical index | Full index

       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual