[R-sig-Geo] Utm to latlong conversion (Datum problem)

[Roger Bivand]

On Tue, 2 Sep 2008, milton ruser wrote:

> Dear all,
>
> I know that it is a knew issue, but I have some troubles
> on the conversion of UTM to Latlong of my shape file.
> In fact, it apears to work but my input file is on South America Datum
> (SAD69),
> but I can´t find the how to indicate the datum. I tryed to include
> "+datum=SAD69"
> on the proj4string, but I received the following error: "unknown elliptical
> parameter name"

It seems that SAD69 is s general description, and you will probably need 
to dig deeper to find the correct +towgs84= values for your data. Add your 
chosen +towgs84= to the CRS for your input data. There are possibly useful 
links in this thread:

http://postgis.refractions.net/pipermail/postgis-users/2006-December/014064.html

or here:

http://osdir.com/ml/gis.proj-4.devel/2006-07/msg00012.html

Try googling SAD69 and towgs84 for lots of different values!

Good luck, don't use the results for navigation without checking, please!

Roger


> Any help are welcome.
>
> Best wishes,
>
> miltinho astronaura
> brazil
> -------------
>
> require(sp)
> require(maptools)
> require(rgdal)
>
> setwd("G:\\HDExt\\R_scripts_genericos\\converte_utm_latlong")
>
> SP<-readShapePoly("area_infl_ind.shp", IDvar=NULL,
> proj4string=CRS("+proj=utm +zone=22 +units=m +south"))
>
> SPll<-spTransform(SP, CRS("+proj=longlat +datum=WGS84"))
>
> 	[[alternative HTML version deleted]]
>
>

-- 
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