[R-sig-Geo] LL to UTM
Gabor Grothendieck
ggrothendieck at gmail.com
Tue Mar 6 15:10:56 CET 2007
Thanks. Looking at ?convUL I see that it also has the
capability of automatically determining the zone. My
zone is fixed so its not a consideration but I will
keep it in mind.
Currently I am using rgdal so Roger's solution
lets me keep within my current framework but I
will check out PBSmapping too at some point.
On 3/6/07, Short, Tom <TShort at epri.com> wrote:
> 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
> > > > >
> > > >
> > > >
> > >
> > > _______________________________________________
> > > R-sig-Geo mailing list
> > > R-sig-Geo at stat.math.ethz.ch
> > > 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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> >
>
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