reading img files with rgdal
Dear Roger, Many thanks for your rapid reply! I guess I was so caught up in the details of rgdal that I completely failed to see that obvious problem. I've managed to fix the coordinates, and now rgdal reads the image just fine. I'm still searching for a good overview of rgdal or gdal though - any pointers would be wonderful. Sincerely, Matt
Roger Bivand wrote:
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