Description of 3.0_patch01

In SLEUTHv3.0beta, road weighting affected the distance of the "random walk" portion of road influenced growth. However, research undertaken primarily at UC Santa Barbara and Penn State University found that this response to road weight was having very little influence in the over all system. As a result, an alternative approach, offered by Dr. Keith Clarke, seems to have a more obvious affect.

Action of modification:

1. Road weighting does not affect the distance of the random walk. Previously, if road weighting was being used, this distance (run_value) was calculated by:

   run_value = (roads(i, j) / max_road_value * dispersion_coefficient)

   where run_value is the maximum number of steps traveled along the road network by an urban pixel. The value of a road pixel at a given location is described by road(i,j). Max_road_value is defined as 100. Run_value is at a maximum of 100 when (road(i,j) == max_road_value) and (dispersion_coefficient == 100).

This behavior has been removed, and run_value is determined only by the dispersion coefficient (the same as it has been when non-weighted roads are being used.)

run_value = dispersion_coefficient

2. Road weighting affects the likelihood of a new spreading center being established at the end of the random walk.
   This probability is calculated by:

   if (random_number <= road_value(i,j))
   {
        create new spreading center
   }

This modification was made in the function spr_road_walk( ) in the spread.c file. (To see the main body of the two functions click here.) The downloadable patch is an entirely new spread.c file. The model must be recompiled after the new file has been placed in the directory containing the code.

Discussion of the application and evolution of SLEUTH is highly encouraged. The discussion board has been created to facilitate the excange of information and ideas. For more information regarding this and other topics, please consult and/or contribute.