[R-sig-Geo] Selecting Random Polygons

[Edzer Pebesma]

require(sp)
# select 20 random polygons:
nysample = nylakes[sample(4466,20),]
plot(nysample)
# sample a single random point inside each polygon:
pts = do.call(rbind,
  lapply(nysample at polygons, spsample, n=1, type="random"))
plot(p, add=TRUE, col='red')

hth,

On 03/21/2014 02:30 PM, Robin Sleith wrote:
> Hello,
> I have a set of spatial polygons (nylakes) and I would like to randomly
> select a number of polygons from nylakes. I do not need an output file of
> polygons necessarily, just a set of points would do. I have tried spsample,
> but it places multiple points per polygon, even when stratified is
> selected. Any thoughts? Info below.
> 
> Thank you
> Robin
> 
>> nylakes
> class       : SpatialPolygons
> features    : 4466
> extent      : -80, -71.88637, 40.29375, 45.48771  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> 
> twenty <- spsample(nylakes, 20, type='random')
> twenty <- spsample(nylakes, 20, type='stratified')
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795

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