[R-sig-Geo] Setting raster x- and y-resolutions equal

[Gregovich, Dave P (DFG)]

Hello,
I have a stack of about 40 rasters with about 1 X 10^7 cells in each. I did not realize it, but it turns out the x-resolution and y-resolution differ at about the 13th decimal point. And I would like to feed this stack into a function (dynatopmodel::upslope.area) that requires xres(x)==yres(x).
Because of the minute difference between the x- and y- resolutions, I am fine just setting the x- and y- resolutions equal to each other. That would save me the time of resampling all of the bands of the stack. However, this does not seem to be working for me when I try to reproduce the problem, as shown below using a single band that mimics a single band from the stack I am working with:

library(raster);library(rgdal)
options(digits=20)

#Example 1, my situation, which is not working....
rast <- raster(nrows=4072, ncols=3111, xmn=656419.81022503704298, xmx=730403.88166906696279,
                                                                ymn=794177.97668560303282,ymx=891016.01555416302290)
rast[] <- rnorm(1:ncell(rast))
proj4string(rast) <- '+init=epsg:26931'
xres(rast);yres(rast)
res(rast)<-c(xres(rast),xres(rast))
#xres and yres differ!!!!....
res(rast)

#and then two examples that work, Example 2, with a raster of the same size but resetting the resolution to res(rast) <- c(5,5)....
rast <- raster(nrows=4072, ncols=3111, xmn=656419.81022503704298, xmx=730403.88166906696279,
                                                                ymn=794177.97668560303282,ymx=891016.01555416302290)
rast[] <- rnorm(1:ncell(rast))
proj4string(rast) <- '+init=epsg:26931'
xres(rast);yres(rast)
res(rast)<-c(5,5)
#new resolution as expected....
res(rast)

#and example 3, with a raster 100X smaller...
rast <- raster(nrows=407, ncols=311, xmn=65641.981022503704298, xmx=73040.388166906696279,
                                                                ymn=79417.797668560303282,ymx=89101.601555416302290)
rast[] <- rnorm(1:ncell(rast))
proj4string(rast) <- '+init=epsg:26931'
xres(rast);yres(rast)
res(rast)<-c(xres(rast),xres(rast))
res(rast)

#salient session info

R version 3.1.3 (2015-03-09)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1
raster_2.3-33      sp_1.0-17  rgdal_0.9-2

Thanks kindly for any help you can provide, r-sig-geo!
__________________________________
Dave Gregovich
Research Analyst
Alaska Department of Fish and Game
Wildlife Conservation Division
Douglas, AK 99821
(907) 465-4291
dave.gregovich at alaska.gov
__________________________________


	[[alternative HTML version deleted]]