[R-sig-Geo] convUL: wrong for Southern hemisphere

[Roger Bivand]

On Sat, 3 Nov 2007, Agustin Lobo wrote:

> Dear list,
>
> For negative latitudes (Southern hemisphere), convUL yields negative UTM
> coordinates as
> for Northern hemisphere, instead of positive UTMY coordinates for the
> South.  I don't see any option for modifying this behavior, is it?
> The same is true for spTransform, can't fnd the way of stating that
> the utm zone is in the Southern hemisphere (which should not be
> required, because of the negative latitude)
> spTransform(tomas1sp, CRS("+proj=utm +zone=19 +ellps=WGS84"))
> yields negative UTMY coordinates and
> spTransform(tomas1sp, CRS("+proj=utm +zone=-19 +ellps=WGS84"))

Well, it is an error. It is not accepted that a negative zone number is 
what is needed to add the y offset. In PROJ.4 notation, you simply add 
+south to the definition:

> library(rgdal)
> CRS("+init=epsg:32719")
CRS arguments:
  +init=epsg:32719 +proj=utm +zone=19 +south +ellps=WGS84 +datum=WGS84
+units=m +no_defs +towgs84=0,0,0

Details at:

http://www.remotesensing.org/geotiff/proj_list/transverse_mercator.html

Other notations may vary, but just assuming that minus indicates south is 
overoptimistic.

Roger

> an error
>
> Agus
>
>

-- 
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