[R-sig-Geo] convUL to convert UTM in Lat/Long

[Roger Bivand]

On Mon, 22 Jan 2007, Berta wrote:

> 
> Hi R-geo users, I am trying to convert a data set in UTM (from Spain,
> zone=30) to the corresponding data set in longitude-latitude. Using
> convUL, it gives me strange results. Here I send my code, just in case
> somebody can tell me what i am missing. I suspect it has something to do
> with + proj or something that it is needed.  Thank you so much in
> advance, Berta
> 
> library(PBSmapping)
> datainUTM<-data.frame(cbind(c(559994, 559673),c(4781905,4781583), c(0, 0), c(1,2)))
> names(datainUTM)<-c("X", "Y", "PID", "POS")
> attr(datainUTM, "projection") <-"UTM"
> attr(datainUTM, "zone") <-30
> datosLL<-convUL(datainUTM)

Yes, can be reproduced, I've CC'ed the maintainer. I can't see anything 
wrong at the R level, but it seems that PBS is maybe expecting the UTM 
coordinates in km not m:

debug: if (inProj == "UTM") {
    inXY <- inXY * 1000
    toUTM <- FALSE
} else {
    toUTM <- TRUE
}

is rather tricky. Doing:

datainUTM$X <-  datainUTM$X/1000
datainUTM$Y <-  datainUTM$Y/1000
convUL(datainUTM)

does work.

Another possibility is:

library(rgdal)
SP <- SpatialPoints(cbind(datainUTM$X, datainUTM$Y), 
  proj4string=CRS("+proj=utm +zone=30"))
spTransform(SP, CRS("+proj=longlat"))

Roger


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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