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define projection for Raster data

2 messages · didimayr, Fischbach, Anthony

didimayr
# 
Hi all,
 

I have a very simple problem, I just want to define a projection for raster
data. However I have no experience with spatial analysis with R, so maybe
someone could give me a hint:
 
My data are radiation raster data for Austria, in .asc-format .
I have the following information:
 
Map projection: geographic (latitude/longitude), ellipsoid WGS84
North: 49N
South: 46:30N
West:  9:30E
East:   17:30E
Resolution 1'30''
 
...giving a total of 100 rows and 320 columns.

Is this information enough to get the right projection and if yes, how do I
define it in R?
 
Thank you so much and kind regards
Dieter Mayr from Vienna

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Fischbach, Anthony
# 
Dear Dieter,
Please refer to the documentation of rgdal and sp.  Also as another newbie
to spatial data in R, I can strongly recommend starting your reading with
Bivand, Pebesma and G?mez-Rubio (2008: Applied Spatial Data Analysis with R. 
Springer).

To cast your raster map into a spatialPixelDataFrame, you will need to write
a script that has these elements.
require(rgdal) 
require(sp)
##read ascii grid using GDAL binding
map <- readGDAL("[your working directory]/map.asc") 
## coerce into a spatialPixelDataFrame
hab <- asc2spixdf(map) 
## Assign a Coordinate Reference System using a PROJ.4 string
prj <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 + 
...[please see http://trac.osgeo.org/proj/wiki/GenParms to set your specific
parameters]")  
proj4string(hab) <- prj

HTH
Anthony



-----
Tony Fischbach, Wildlife Biologist
Walrus Research Program
Alaska Science Center
U.S. Geological Survey
4210 University Drive
Anchorage, AK 99508-4650

AFischbach at usgs.gov
http://alaska.usgs.gov/science/biology/walrus
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