spTransform / SpatialPixelsDataFrame
On Thu, 21 Apr 2016, twah at gmx.ch wrote:
Hello
I would like to reproject a SpatialPixelsDataFrame, changing the CRS. I am
trying to use the command "spTransform" from the package "sp". Unfortunately,
the command results in a SpatialPointsDataFrame, which is not desired. My
SpatialPixelsDataFrame has proj4string
+init=epsg:21781 +proj=somerc +lat_0=46.95240555555556
+lon_0=7.439583333333333 +k_0=1 +x_0=600000 +y_0=200000 +ellps=bessel
+towgs84=674.4,15.1,405.3,0,0,0,0
+units=m +no_defs
The command which results in a SpatialPointsDataFrame is:
SPDF2<-spTransform(SPDF1,CRS("+proj=longlat +datum=WGS84 +ellps=WGS84
+towgs84=0,0,0"))
An object transformation through
SPDF3<-as(SPDF2,"SpatialPixelsDataFrame")
results in an error, possibly since in the underlying problem the SPDF2 is a
subset for a particular layer, so it is not a full grid.
Can someone help?
You cannot in general project grids, because the spacings between cell centre points will no longer be fixed. You can convert to a raster object and *warp* that grid to a new grid in the new projection with regularly spaced points, but with output cell centre points that do not match the projected points. Often, interpolation is needed to decide which value should be assigned to the output grid cells. Roger
Thanks.
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Roger Bivand Department of Economics, Norwegian School of Economics, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 91 00 e-mail: Roger.Bivand at nhh.no http://orcid.org/0000-0003-2392-6140 https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en http://depsy.org/person/434412