[R-sig-Geo] SpTransform problem : conversion from WGS84 to UTM32N unregular

[FVASBIEN at atmo-alsace.net]

Hi list,

I use a kriging package for several years and it works successfully in my
automated air-quality forecasting chain, by using old versions of
libraries(e.g. 2009/2010 versions of sp, rgdal, …).
Currently, I’ve to change of server (from 32 bits to 64 bits) and I’ve
installed the same package (and so the last delivered versions of
libraries) on this new server.

I encounter an annoying problem: by using strictly the same package and the
same inputs data, the conversion of grids from Lon-Lat WGS84 (irregular
grid) to UTM32 doesn’t lead to a strictly regular grid, and this leads to a
problem for the kriging process.
By using the old libraries versions, the UTM32 grid obtained is strictly
regular with a step of 3km !

Concretely, my package begins by extracting the longitude and latitude of
my CTM model outputs at 3km resolution. I assign to these data the WGS84
projection via the attribute "CRS (" + init = epsg: 4326 ")". After this
treatment, I obtain as expected a list of lon-lat on each cell centroide.
This is the next step which raises concern: to convert this grid into a
regular grid, I apply the grid conversion into utm32 via the spTransform
package and the attribute "CRS ("+proj=utm +zone=32 +ellps=intl
+towgs84=-87, -96 , -120 +units=m +no_defs”)". My domain covers the East of
France and goes across Germany, hence the “towgs84” params added.
After this treatment, I obtain the coordinates of my grid in UTM32 North
zone, but these are not strictly regular (decimal data appear) and the step
never strictly equals to 3km.

Does anyone have any feedback or experience about my problem ? I thought to
an update in the attributes of the spTransform package, but I’ve found no
answer yet…
Any information regarding my problem would be nice !

Thanks you,

Greetings,
Florent.