Random Sampling from huge point data

Question

Hi everyone,

I have 35,000 points datasets. It is tedious to incorporate all points for my analysis. I am trying to generate random sample points in ArcGIS 9.3.1 platform. Is it possible run sampling technique in ArcGIS 9.3.1?

Any kind of suggestion is welcome.

Thanks!

MichaelMcManus · Answer

The R package spsurvey can draw random samples, as well as spatially balanced probabilistic samples, so you might check out that package.  Here is a web site that describes some survey applications using spsurvey:
http://www.epa.gov/nheerl/arm/

Mike

JeffreyEvans · Answer

Here is code in R. It requires the rgdal library. If you search around the forum there are some example scripts for calling R from ArcMap. Here is one example form the ESRI scripts page. http://resources.arcgis.com/gallery/file/geoprocessing/details?entryID=F855D6D1-1422-2418-A0B2-643E624A8925 ################################################################## # PROGRAM: RandomFeatureSample.R # USE: RANDOM SAMPLING OF SPATIAL OBJECTS # REQUIRES: SP CLASS SpatialDataFrame OBJECT # # FUNCTIONS: # RandSP(x, ns=10, reps=1, replace=FALSE) # # ARGUMENTS: # x SP CLASS SpatialDataFrame OBJECT (POINT, POLYGON, LINE, PIXEL) # n NUMBER OF RANDOM SAMPLES # reps NUMBER OF REPLICATES (STRATA) # replace SAMPLE WITH REPLACEMENT (DEFAULT FALSE) # ... OPTIONAL ARGUMENTS TO PASS TO sample # # VALUE: # SUBSAMPLE OF SP FEATURECLASS AS SAME SP CLASS # # NOTES: # IF REPLACEMENT IS FALSE FEATURES ARE REMOVED FROM CONSIDERATION IN SUBSEQUENT # REPS # THIS MEANS THAT IF TRUE, THAT A FEATURE CAN BE SELECTED MULTIPLE TIMES ACROSS # REPLICATES. NOT RELEVANT IF REP=1. # # EXAMPLES: # require(rgdal) # require(sp) # # READ SHAPEFILE USING RGDAL # shape <- readOGR(dsn="C:/test", layer="polys", driver="ESRI Shapefile") # # # CREATES 4 REPLCATES WITH 5 RANDOM SAMPLES EACH WITHOUT REPLACEMENT # ssample <- RandSP(shape, n=5, reps=4, replace=FALSE) # # # CREATES 1 REPLCATE WITH 10% RANDOM SAMPLE WITHOUT REPLACEMENT # ssample <- RandSP(shape, n=round(dim(shape)[1]*0.10), digits=0), reps=1, replace=FALSE) # # # WRITE RANDOM SAMPLE SHAPEFILE USING RGDAL # writeOGR(ssample, dsn="C:/test", layer="RandSample", driver="ESRI Shapefile") # # # PLOT RANDOM SAMPLES COLORED BY REPLICATE # spplot(ssample, "REP", col.regions=terrain.colors(n=length(unique(ssample@data$REP)))) # # REFERENCES: # B.D. Ripley, 1981. Spatial Statistics, Wiley # # CONTACT: # Jeffrey S. Evans # Senior Landscape Ecologist # The Nature Conservancy - Central Science # Laramie, WY # (970)672-6766 # jeffrey_evans@tnc.org ################################################################## RandSP <- function(x, n=10, reps=1, replace=FALSE, ...) { if (!require(sp)) stop("sp PACKAGE MISSING") if (!inherits(x@data, "data.frame")) stop("MUST BE SP SpatialDataFrame OBJECT") spx <- x if ( dim(spx)[1] > n ) { s <- sample(1:nrow(spx@data), n) results <- spx[s, ] results@data <- data.frame(results@data, REP=1) if(replace==FALSE) { spx <- spx[-s, ] } if(reps > 1) { for (i in 2:reps ) { s <- sample(1:nrow(spx@data), n) ssamp <- spx[s, ] ssamp@data <- data.frame(ssamp@data, REP=i) results <- rbind(results, ssamp) if(replace==FALSE) { spx <- spx[-s, ] } } } } return( results ) }