Hi Roger,
I apologize for multiple posting.  I thought the list automatically posts
the questions and  didn't know the questions go through admin before being
posted.  I'll be patient next time...




On Mon, Nov 12, 2012 at 2:40 PM, Roger Bivand <Roger.Bivand@nhh.no> wrote:

> Patience is a virtue - this is your third identical posting on this topic.
> Please do respect the time list members give. Please also read the list
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> On Mon, 12 Nov 2012, dani jon wrote:
>
>  Dear List,
>> I am interested in overlaying a regular polygon grid of 8 by 8 into a
>> spatial surface. Essentially, dividing the spatial surface into 64 polygon
>> grids and would like to take a sample of 10 points (pixels) with
>> corresponding xy coordinate and values for each of the 64 grids.  Here is
>> my attempt.
>>
>> library(maptools)
>> library(raster)
>> library(sp)
>> library(gstat)
>> library(maps)
>>
>> ## Creating spatial surface
>>
>> xg = seq(1, 100,, 100)
>> yg = seq(1, 100,, 100)
>> xy = expand.grid(xg, yg)
>> names(xy) <- c("x","y")
>> g.dummy <- gstat(formula=z~1, locations=~x+y, dummy=T, beta=1,
>> model=vgm(psill=0.025,model="
>> Exp",range=15), nmax=20)
>> yy <- predict(g.dummy, newdata=xy, nsim=1)
>> gridded(yy) = ~x+y
>> coor.yy <- coordinates(yy[1])
>> ytrue <-yy[1]@data
>> yyspdf<- SpatialPointsDataFrame(coords=**coor.yy, data=ytrue)
>> yyspdf[1:10,]
>> coordinates     sim1
>> 1       (1, 1) 1.305260
>> 2       (2, 1) 1.287697
>> 3       (3, 1) 1.219094
>> 4       (4, 1) 1.333913
>> 5       (5, 1) 1.268508
>> 6       (6, 1) 1.263417
>> 7       (7, 1) 1.243237
>> 8       (8, 1) 1.276870
>> 9       (9, 1) 1.231528
>> 10     (10, 1) 1.162322
>>
>> ## creating regular polygon grid (8x8)
>>
>> grd <- GridTopology(c(6.3,6.3), c(12.5,12.5), c(8,8))
>> SpP_grd <-as.SpatialPolygons.**GridTopology(grd)
>> plot(SpP_grd)
>> text(coordinates(SpP_grd), sapply(slot(SpP_grd, "polygons"), function(i)
>> slot(i, "ID")), cex=0.5)
>> ids <- sapply(slot(SpP_grd, 'polygons'), function(i) slot(i, 'ID'))
>> trdata <- data.frame(A=rep(c(1,2,3,4,5,**6,7,8), 8),
>> B=rep(c(1,2,3,4,5,6,7,8), each=8),
>> row.names=sapply(slot(SpP_grd, "polygons"), function(i) slot(i, "ID")))
>> SpPDF <- SpatialPolygonsDataFrame(SpP_**grd, trdata)
>> SpPDF@data = cbind(SpPDF@data,ids)
>>
>>  SpPDF@data[1:10,]
>>>
>>    A B ids
>> g1  1 1  g1
>> g2  2 1  g2
>> g3  3 1  g3
>> g4  4 1  g4
>> g5  5 1  g5
>> g6  6 1  g6
>> g7  7 1  g7
>> g8  8 1  g8
>> g9  1 2  g9
>> g10 2 2 g10
>>
>> ## Overlay
>> image(yy[1])
>> plot(SpPDF, border="magenta", add=TRUE)
>> text(coordinates(SpP_grd), sapply(slot(SpP_grd, "polygons"), function(i)
>> slot(i, "ID")), cex=0.5)
>>
>> My question is how to overlay yy[1] and SpPDF and take 10 samples within
>> each polygon grid (g1-g64) and extract the values and coordinates of
>> yy[1]?  So I will have an output with a sample of 640
>>
>> x  y   sim1        ids
>> 1  2   1.305260   g1
>> 1 3 1.02567     g1
>> .
>> .
>> 95 95 1.3487    g64
>>
>> Edzer  suggested something likes this, but it does not exactly  640
>> samples
>> (10*64) as I wanted.
>>
>> x = do.call(rbind, lapply(1:10, function(x) spsample(yy, cellsize = 12.5,
>> type = "stratified")))
>>
>> Thanks in advance
>> Best regards
>> Sam
>>
>>         [[alternative HTML version deleted]]
>>
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>>
>>
> --
> Roger Bivand
> Department of Economics, NHH Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand@nhh.no
>
>

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