[R-sig-Geo] reading img files with rgdal

[Roger Bivand]

On Wed, 11 Jul 2007, Matthew Landis wrote:

> Dear R-sig-Geo,
>
> I'm trying to get started with rgdal, and not having much luck so far.
> I'm running R 2.5.0 on an i386-pc-mingw32 with rgdal 0.5-9 and sp 0.9-14.
>
> For starters, I'd like to read in an .img file created in ArcGIS 9.2. As
> you can see below, the file is a global map in geographic coordinates
> with 0.5 degree resolution.
>
> > GDALinfo('swe20070615.img')
> Closing GDAL dataset handle 0x020d8660...  destroyed ... done.
> rows        360
> columns     720
> bands       1
> ll.x        -180
> ll.y        90.0321

This is the problem, since > 90N is not defined for geographical 
coordinates, and leads to the projection being rejected. Why Arc wants to 
believe in > 90N is probably not known. If you can find out where the fuzz 
is coming from, perhaps you can remove it?  If correcting the data is not 
an option, please ask again, and a work-round may be possible (reading the 
data without its projection information, and placing it in a correct 
grid).

Roger

> res.x       0.5
> res.y       0.5
> oblique.x   0
> oblique.y   0
> driver      HFA
> projection  +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
> file        swe20070615.img
>
> The result of readGDAL is initially promising, but ultimately fails,
> apparently due to a problem with the projection.
>
> > test <- readGDAL('swe20070615.img')
> swe20070615.img has GDAL driver HFA
> and has 360 rows and 720 columns
> Closing GDAL dataset handle 0x056988a8...  destroyed ... done.
> Closing GDAL dataset handle (nil)... done.
> Closing GDAL dataset handle 0x020dade8...  destroyed ... done.
> Closing GDAL dataset handle 0x05699470...  destroyed ... done.
> Error in `proj4string<-`(`*tmp*`, value = <S4 object of class "CRS">) :
>        Geographical CRS given to non-conformant data
> > str(test)
> Error in str(test) : object "test" not found
>
> Can anyone suggest what might be going wrong and how to fix it?
>
> In addition, I've had some trouble finding a good point of entry for how
> to use rgdal.  I have checked the standard documentation in the R help
> files and the GDAL websites, but having a bit of trouble penetrating it
> all.  If anyone can point me to a concise overview of how to use rgdal,
> I'd be most grateful.
>
> Many thanks in advance,
>
> Sincerely,
>
> Matt Landis
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no