change projection?
On Thu, 22 Nov 2007, Ingo Holz wrote:
Hi, I imported a ESRIAsciiGrid with readGDAL(). The result is a
SpatialGridDataFrame (SGDF).
The projection of the grid (only the xllcorner, yllcorner ?) is: Projection LAMBERT Units METERS Spheroid BESSEL (more details at the end of this email)
You should be able to construct a string to represent this projection (which is more likely +proj=lcc than +proj=laea), although I cannot see it in the EPSG list as such.
How can I change this to gauss-krueger projection zone 3 (gk3)?
This is a different projection, which means that the regular raster cells in the input will become irregular polygons in the output in general, and you need to warp from one to the other. You can interpolate to a regular grid in the output projection using standard interpolation tools.
I did not specify the projection in the SGDF, how is this done?
proj4string(SGDF) <- CRS("<myprj>")
or if a *.prj file is present, readGDAL() may detect it.
Roger
summary(SGDF):
Closing GDAL dataset handle (nil)... done.
Object of class SpatialGridDataFrame
Coordinates:
min max
x -250000 500000
y 20000 1020000
Is projected: NA
proj4string : [NA]
Number of points: 2
Grid attributes:
cellcentre.offset cellsize cells.dim
x -249500 1000 750
y 20500 1000 1000
Data attributes:
band1
Min. : 812
....
There should be a simple way to use library(proj4) to make this transformation?
Are I am right that actually only the "xllcorner, yllcorner"-values are transformed?
Where can I find an easy (and maybe short) introduction to this topic?
Thank you,
Ingo
######
Description of Grid ...*
Cell Size (meters) = 1000.000 Data Type:
Integer
Number of Rows = 1000 Number of Values = ....*
Number of Columns = 750 Attribute Data (bytes) = ...*
BOUNDARY: STATISTICS:
Xmin = -250000.000 Minimum Value = ...*
Xmax = 500000.000 Maximum Value = ...*
Ymin = 20000.000 Mean = ...*
Ymax = 1020000.000 Standard Deviation = ...*
COORDINATE SYSTEM DESCRIPTION
Projection LAMBERT
Units METERS
Spheroid BESSEL
Parameters:
1st standard parallel 50 0 0.000
2nd standard parallel 51 0 0.000
central meridian 9 0 0.000
latitude of projection's origin 47 0 0.000
false easting (meters) 0.00000
false northing (meters) 0.00000
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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