Raster projection alignment issues
Wade, I was able to import the data into GRASS GIS (which uses gdal) without any problems (ultimately); the issue you're having is that the ACTUAL map projection is either not specified -OR- is specified as 'unprojected', which is what I think is the case. In reality, the map projection is latitude-longitude and the data is written that way within the netcdf file. In GRASS GIS I simply imported the data (a 1-commandline step) directly into a latitude-longitude GRASS GIS LOCATION, which I already had setup. I tested by over-laying U.S. state boundaries, which align perfectly. That the crs is defined as Albers Equal Area in the data set is CLEARLY an error. Personally, I think you would be far better served to use something like GRASS GIS for this kind of work; I have had a lot of success doing this. One very nice feature is that GRASS GIS plays together with R wonderfully, through the spgrass6 contributed package. Going this direction, allows one to read/write GRASS raster and vector files into/from R and do any and all the statistical manipulations you want. Additionally, I think for many things, you'll find you don't need R, like simple data visualization and most raster arithmetic. Best, Tom On Fri, Dec 19, 2014 at 7:34 AM, Wall, Wade A ERDC-RDE-CERL-IL <
Wade.A.Wall at usace.army.mil> wrote:
Hi all, I posted this over at gis.stackexchange.com, but thought this user group may be interested. I downloaded raster data from http://gdo-dcp.ucllnl.org/downscaled_cmip_projections/dcpInterface.html#Welcomein The BCSD-CMIP5 data is found under the tab "Projections: Complete Archives". The files are in netCDF format, but am running into some issues. The original raster data (let's call it rast1) when imported has the extent xmin 235.25 xmax 293 ymin 25.125 ymax 52.875 and a crs of +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 The other objects (both sp and raster) I am working with contain negative values for xmin and xmax xmin : -122.8021 xmax : -75.38249 ymin : 31.78881 ymax : 47.15952 When I attempt to reproject the raster data into Albers Equal Area (+proj=aea +lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-96 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs +ellps=GRS80+towgs84=0,0,0)using the following code: rast_new = projectRaster(rast1, rast2) ## rast2 is a raster with the crs for Albers Equal Area the extents still don't line up, so I have to do the following. rast_new = projectExtent(rast1,rast2) rast_new = projectRaster(rast1,rast_new) values(rast_new) = values(rast1) ### This is necessary because all the values were NA However, rast_new, even though its crs is defined as Albers Equal Area, does not project correctly. Even when I export these files from R and open in ArcGIS, the issues persist. However, if I import the netCDF files directly into ArcGIS and reproject, there are no problems. Any clues as to what I am doing wrong? Thanks for any assistance. Wade A. Wall US Army ERDC-CERL P.O. Box 9005 Champaign, IL 61826-9005 1-217-373-4420 Wade.A.Wall at usace.army.mil [[alternative HTML version deleted]]
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo