Random Sampling from huge point data

MilanBudhathoki1 — Thu, 19 May 2011 01:06:50 GMT

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!

Re: Random Sampling from huge point data

JeffreyEvans — Sat, 11 Dec 2021 07:23:46 GMT

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 )
 }

Re: Random Sampling from huge point data

MichaelMcManus — Mon, 23 May 2011 19:09:53 GMT

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

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Random Sampling from huge point data

Re: Random Sampling from huge point data

Re: Random Sampling from huge point data