Provided by: grass-doc_7.6.0-1_all

**NAME**

r.random.cells- Generates random cell values with spatial dependence.

**KEYWORDS**

raster, sampling, random, autocorrelation

**SYNOPSIS**

r.random.cellsr.random.cells--helpr.random.cellsoutput=namedistance=float[ncells=integer] [seed=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]Flags:--overwriteAllow output files to overwrite existing files--helpPrint usage summary--verboseVerbose module output--quietQuiet module output--uiForce launching GUI dialogParameters:output=name[required]Name for output raster mapdistance=float[required]Maximum distance of spatial correlation (value >= 0.0)ncells=integerMaximum number of cells to be created Options:1-seed=integerRandom seed, default [random]

**DESCRIPTION**

r.random.cellsgenerates a random sets of raster cells that are at leastdistanceapart. The cells are numbered from 1 to the numbers of cells generated, all other cells are NULL (no data). Random cells will not be generated in areas masked off.DetailedparameterdescriptionoutputRandom cells. Each random cell has a unique non-zero cell value ranging from 1 to the number of cells generated. The heuristic for this algorithm is to randomly pick cells until there are no cells outside of the chosen cell’s buffer of radiusdistance.distanceDetermines the minimum distance the centers of the random cells will be apart.seedSpecifies the random seed thatr.random.cellswill use to generate the cells. If the random seed is not given,r.random.cellswill get a seed from the process ID number.

**NOTES**

The original purpose for this program was to generate independent random samples of cells in a study area. Thedistancevalue is the amount of spatial autocorrelation for the map being studied.

**EXAMPLE**

RandomcellsingivendistancesNorth Carolina sample dataset example: g.region n=228500 s=215000 w=630000 e=645000 res=100 -p r.random.cells output=random_500m distance=500LimitednumberofrandompointsHere is another example where we will create given number of vector points with the given minimal distances. Let’s star with setting the region (we use large cells here): g.region raster=elevation g.region rows=20 cols=20 -p Then we generate random cells and we limit their count to 20: r.random.cells output=random_cells distance=1500 ncells=20 seed=200 Finally, we convert the raster cells to points usingr.to.vectmodule: r.to.vect input=random_cells output=random_points type=point An example of the result is at the Figure below on the left in comparison with the result without the cell limit on the right. Additionally, we can usev.perturbmodule to add random spatial deviation to their position so that they are not perfectly aligned with the grid. We cannot perturb the points too much, otherwise we might seriously break the minimal distance we set earlier. v.perturb input=random_points output=random_points_moved parameters=50 seed=200 In the above examples, we were using fixed seed. This is advantageous when we want to generate (pseudo) random data, but we want to get reproducible results at the same time.Figure:Generatedcellswithlimitednumberofcells(upperleft),derivedvectorpoints(lowerleft),cellswithoutacountlimit(upperright)andcorrespondingvectorpoints(lowerright)

**REFERENCES**

Random Field Software for GRASS GIS by Chuck Ehlschlaeger As part of my dissertation, I put together several programs that help GRASS (4.1 and beyond) develop uncertainty models of spatial data. I hope you find it useful and dependable. The following papers might clarify their use: · Ehlschlaeger, C.R., Shortridge, A.M., Goodchild, M.F., 1997. Visualizing spatial data uncertainty using animation. Computers & Geosciences 23, 387-395. doi:10.1016/S0098-3004(97)00005-8 · Modeling Uncertainty in Elevation Data for Geographical Analysis, by Charles R. Ehlschlaeger, and Ashton M. Shortridge. Proceedings of the 7th International Symposium on Spatial Data Handling, Delft, Netherlands, August 1996. · Dealing with Uncertainty in Categorical Coverage Maps: Defining, Visualizing, and Managing Data Errors, by Charles Ehlschlaeger and Michael Goodchild. Proceedings, Workshop on Geographic Information Systems at the Conference on Information and Knowledge Management, Gaithersburg MD, 1994. · Uncertainty in Spatial Data: Defining, Visualizing, and Managing Data Errors, by Charles Ehlschlaeger and Michael Goodchild. Proceedings, GIS/LIS’94, pp. 246-253, Phoenix AZ, 1994.

**SEE** **ALSO**

r.random.surface,r.random,v.random,r.to.vect,v.perturb

**AUTHOR**

Charles Ehlschlaeger; National Center for Geographic Information and Analysis, University of California, Santa Barbara.Lastchanged:$Date:2015-10-1022:01:15+0200(Sat,10Oct2015)$

**SOURCE** **CODE**

Available at: r.random.cells source code (history) Main index | Raster index | Topics index | Keywords index | Graphical index | Full index © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual