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: [EMAIL PROTECTED]
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