[R-sig-Geo] Problem with spTransform() function

[ASANTOS]

Dear Members,

     I have a problem with spTransform() function, when I try to use a 
object in UTM Zone 23K south and project in latlong south. First, I have 
a polygon SP object in UTM ( CRS("+proj=utm +zone=23+south +datum=WGS84 
+units=m +no_defs"))

     > bbox(SP)
         min       max
x  772259.1  775259.1
y 7840046.0 7843046.0

   But if a using spTransform() for latlong (CRS("+proj=longlat +south 
+datum=WGS84")):

 > bbox(SPlatlong)
         min       max
x -37.67016 -37.58043
y  70.51439  70.54432

  There are something wrong, because the min values are x -37.67016 and 
y 70.51439, but I suppose to be x -42.4058069902 and y -19.5157348241. 
What's the conversion problem?

My example:


require(sp)
require(rgdal)

# Create one point in UTM
xcc<-773759.1
ycc<-7841546
p.central<-cbind(xcc,ycc) ##Centroid

###Countour area
coordV<-NULL
coordV 
<-rbind(coordV,cbind(p.central[,1]+c(-1500,1500,1500,-1500,-1500),p.central[,2]+c(1500,1500,-1500,-1500,1500)))
plot(coordV[,1],coordV[,2])
points(p.central[,1],p.central[,2], col="red")
#

# Creat a polygon
bnds <- cbind(x=c(coordV[,1]), y=c(coordV[,2]))

# Convert in spatial polygon and project in UTM Zone 23K
SP <- SpatialPolygons(list(Polygons(list(Polygon(bnds)), "1")))
proj4string(SP) = CRS("+proj=utm +zone=23+south +datum=WGS84 +units=m 
+no_defs") ## Projeção

# Reproject the same area in latlong south
SPlatlong<- spTransform(SP, CRS("+proj=longlat +south +datum=WGS84"))
#

Thanks,

-- 
======================================================================
Alexandre dos Santos
Proteção Florestal
IFMT - Instituto Federal de Educação, Ciência e Tecnologia de Mato Grosso
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         alexandre.santos at cas.ifmt.edu.br
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