[R-sig-Geo] LL to UTM

[Short, Tom]

Gabor, 

I've used convUL in the PBSmapping package to convert from UTM to
lat/lon for some weather data I was playing with. It will also convert
from lat/lon to UTM (I haven't tried that direction though).

Here's the code I used:

  library(PBSmapping)  
  subs = read.csv("ngrid/SubAsPoints.csv", comment="")
  names(subs) = tolower(names(subs))
  attr(subs, "zone") = 18
  attr(subs, "projection") = "UTM"
  subs$X = subs$point_x * 12 * 2.54 / 1e5 # convert to km
  subs$Y = subs$point_y * 12 * 2.54 / 1e5
  subs$sub_num = subs$sub_number
  subs = convUL(subs)

Here's the code from the help file for converting the other way:

  data(nepacLL)
  #--- set the zone attribute
  attr(nepacLL, "zone") <- 9
  #--- convert to UTM
  nepacUTM <- convUL(nepacLL)

- Tom

Tom Short
EPRI
  

> -----Original Message-----
> From: r-sig-geo-bounces at stat.math.ethz.ch 
> [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Roger Bivand
> Sent: Tuesday, March 06, 2007 8:28 AM
> To: Gabor Grothendieck
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: [R-sig-Geo] LL to UTM
> 
> On Tue, 6 Mar 2007, Gabor Grothendieck wrote:
> 
> > Thanks. I looked at spTransform prior to posting but don't 
> understand it.
> > What I want is to create a function that returns UTM coordinates:
> > 
> > LL2UTM <- function(lat, long, zone = 18) { ...
> > }
> 
> library(rgdal)
> LL2UTM <- function(lat, long, zone=18) {
>   project(cbind(long, lat), paste("+proj=utm +zone=", zone, sep="")) }
> 
> gets you there, for example for:
> 
> lat <- seq(30,45,1)
> long <- seq(-78,-72,1)
> grd <- expand.grid(lat, long)
> LL2UTM(grd[,1], grd[,2])
> 
> The project() interface to PROJ4 does not support datum 
> transfromation, the spTransform() method does. The cost is 
> having to convert the data to a Spatial* object:
> 
> SP_grd <- SpatialPoints(cbind(grd[,2], grd[,1]),
>   proj4string=CRS("+proj=longlat +datum=NAD83"))
> SP_grd1 <- spTransform(SP_grd, CRS("+proj=utm +zone=18 +datum=NAD83"))
> 
> returning a SpatialPoints object - use the coordinates() 
> method to retrieve as a matrix.
> 
> Assuming that your input geographical coordinates are in 
> NAD84/WGS84, and the output UTM coordinates are in the same 
> datum, project() will be OK. If you need datum 
> transformation, which may lead to errors of hundreds of 
> metres if not used, the PROJ4 string needs more detail. If 
> this is at the block scale, datum transformation will make a 
> difference if the input and output specifications vary (say 
> placing points on a UTM map not in WGS84/NAD83). At the 
> continental scale the differences are typically not great, 
> but then you wouldn't use UTM anyway.
> 
> Hope this helps,
> 
> Roger
> 
> > 
> > If necessary, zone=18 can be hardcoded in the function and that arg 
> > removed.
> > 
> > I assume that using spTransform its just a one line body. 
> Can you give 
> > me the specific line that it should be?
> > 
> > Thanks.
> > 
> > 
> > On 3/6/07, Edzer J. Pebesma <e.pebesma at geo.uu.nl> wrote:
> > > Gabor,
> > >
> > > package rgdal provides an interface to the PROJ.4 library for 
> > > projection of geographical data. Look for the function (or rather 
> > > method) spTransform. It takes any of the spatial classes 
> provided by 
> > > package sp, and afaik any of the known projection 
> systems, including 
> > > UTM and ellipsoids (LL reference "model").
> > > --
> > > Edzer
> > >
> > > Gabor Grothendieck wrote:
> > > > I am currently using this web page to convert LL to UTM 
> (and UTM to LL).
> > > >
> > > >    http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html
> > > >
> > > > All my points are in zone 18.  How would I accomplish the same 
> > > > thing using R?
> > > >
> > > > Thanks.
> > > >
> > > > _______________________________________________
> > > > R-sig-Geo mailing list
> > > > R-sig-Geo at stat.math.ethz.ch
> > > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > > >
> > >
> > >
> > 
> > _______________________________________________
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> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > 
> 
> --
> 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
> 
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