[R-sig-Geo] Problem with cell numbers when using a raster extent object

[Ned Horning]

Hi -

I have a script that calculates a common extent between two images than 
then uses the resulting extent to restrict the random selection of cells 
from a raster using the “sampleRandom” function. I use the following 
function:

sampleCells <- sampleRandom(predImage, size=numSamps, cells=TRUE, 
extent=commonExt)[,1]

Next I use "xyFromCell(predImage, sampleCells[i])" to calculate the 
coordinates of the center of a cell and all of the cell centers fall 
outside of the extent that I am using. Using "sp=TRUE" I get a similar 
result - all of the points are outside of the extent:

sampleCells <- sampleRandom(predImage, size=numSamps, sp=TRUE, 
ext=commonExt)

To get around this problem I tried to physically clip the image before 
running “sampleRandom” and the results are similar. The following line 
also produces cells that are outside of the extent “commonExt” when I 
use “xyFromCell”:

sampleCells <- sampleRandom(crop(predImage,commonExt), size=numSamps, 
ext=commonExt, na.rm=TRUE)

However, if I run the following line using"clip" and "sp=TRUE" the 
sample points fall within the extent:

sampleCells <- sampleRandom(crop(predImage,commonExt), size=numSamps, 
sp=TRUE, ext=commonExt, na.rm=TRUE)

So, there is a work-around but I'd prefer not to have the overhead of 
clipping the image.

This seems somewhat similar to a problem I reported a few months ago and 
was fixed. Can anyone replicate this problem? Am I doing something wrong?

I am using R version: 3.0.2 and Raster package version: 2.1-49 on Ubuntu 
12.04 64 bit

Ned