[R] spTransform longlat to utm
Alexander Belousov
mynewsmailbox at gmx.de
Thu Oct 18 17:32:18 CEST 2012
Dear all,
I am trying to project my LongLat-maps to a plane.
The ultimate purpose is to do a search of points in vicinity of other points using overlay-commands (sp) with radius in km.
I am applying spTransform (package rgdal) and it gives my some curious results.
An example.
Let's take a point lying somewhere in Germany, zone=32U
x <- 8.968735
y <- 49.454735
After conversion I sould get something like
Easting: 426858 (km)
Northing: 5427937 (km)
sp1 <- SpatialPoints(matrix(c(x,y), ncol=2), proj4string = CRS("+proj=longlat +datum=WGS84"))
sp1Transformed <- spTransform(sp1, CRS("+proj=merc +zone=32u +datum=WGS84"))
coordinates(sp1Transformed)
coords.x1 coords.x2
[1,] 998395.0133 6319888.068
The result is an obvious nonsense.
Well, after some deliberation I swapped the original coordinate columns:
x <- 49.454735
y <- 8.968735
sp2 <- SpatialPoints(matrix(c(x,y), ncol=2), proj4string = CRS("+proj=longlat +datum=WGS84"))
sp2Transformed <- spTransform(sp2, CRS("+proj=merc +zone=32u +datum=WGS84"))
coordinates(sp2Transformed)
coords.x1 coords.x2
[1,] 5505275.918 995840.692
Now the northing (which comes first after swapping) looks better, at least it falls within Germany, which is however not to say about the easting.
Apparently I am missing an important point by the transformation.
Any help will be greatly appreciated!
Regards
Alex
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