Werner Wernersen wrote:
It would be nicer to convert directly the entire shapefile object to long/lat
coordinates but if that is not possible, I will convert the other points to UTM.
Hence, I am playing around with rgdal.
library(rgdal)
SP <- SpatialPoints(cbind(32.29252, -0.3228500),
proj4string=CRS("+proj=longlat"))
spTransform(SP, CRS("+proj=utm +zone=36"))
spTransform(SP, CRS("+proj=utm +zone=36"))
SpatialPoints:
coords.x1 coords.x2
[1,] 421274.4 -35687.37
Coordinate Reference System (CRS) arguments: +proj=utm +zone=36 +ellps=WGS84
This result corresponds with what I get when using convUL() but my map of that
area in UTM coordinates does not extend to the negative.
An external program converts the point to x=420994 y=9964407 which also seems
correct with respect to the map. Fore sure, I am using the function wrongly
somehow. Can anyone give me a hint?
It looks like you are specifying 36S in your external program, and
(implicitly) 36N in R. Using your SP from above, note the following:
> spTransform(SP, CRS("+proj=utm +zone=36 +north"))
SpatialPoints:
coords.x1 coords.x2
[1,] 421274.4 -35687.37
Coordinate Reference System (CRS) arguments: +proj=utm +zone=36
+ellps=WGS84
> spTransform(SP, CRS("+proj=utm +zone=36 +south"))
SpatialPoints:
coords.x1 coords.x2
[1,] 421274.4 9964313
Coordinate Reference System (CRS) arguments: +proj=utm +zone=36 +south
+ellps=WGS84
The latter gets in the ballpark of output from your external program.
I'd speculate that the remaining differences owe to different
assumptions about e.g. the datum (WGS84 for the R statements given
above), but I must admit I'm not a geographer.
Hope that helps,
Jim
That's very much appreciated!
Thanks,
Werner
----- Ursprüngliche Mail ----
Von: Werner Wernersen <[EMAIL PROTECTED]>
An: [EMAIL PROTECTED]
Gesendet: Dienstag, den 19. August 2008, 20:28:29 Uhr
Betreff: converting coordinates from utm to longitude / latitude
Hi,
is there a function in R to convert data read with read.shape and which is
originally in UTM coordinates into longitude / latitude coordinates?
I found the convUL() function from the PBSmapping package but I have no idea
how I could apply that to the read.shape object.
Many thanks,
Werner
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