[R-sig-Geo] spTransform: wrong results??

[Agustin Lobo]

I'm finding conflicting results at comparing
results of converting UTM ED50 coordinates
to lon,lat WGS84 using spTransform() (thus, proj4)
and other programs such as GlobalMapper and Compegps.

My main surprise is that spTransform() yields the same result
whatever the ellps field for the inverse transform. This is
what I'm doing with the meuse dataset as an example, you can
see that the results of the inverse transform to lon,lat WGS84 are identical to
those to lon,lat ED50, both starting from UTM50 or from UTMWGS84

At the end
I include results with GlobalMapper for the first point. Results
with GlobalMapper do differ for lon,lat WGS84 and lon,lat ED50

Any help would be appreciated, as I'm doing all my work
in UTM ED50 but have to pass the coordinates as lon,lat WGS84
for the flight.

data(meuse)
coordinates(meuse) <- c("x", "y")
proj4string(meuse) <- CRS("+proj=stere +lat_0=52.15616055555555 
+lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel 
+units=m")
meuse.utm <- spTransform(meuse, CRS("+proj=utm +zone=32 +ellps=WGS84"))
coordinates(meuse.utm)[1:3,]
             x       y
[1,] 272571.9 5653978
[2,] 272522.4 5653927
[3,] 272661.2 5653899

meuse.utmintl <- spTransform(meuse, CRS("+proj=utm +zone=32 +ellps=intl"))
coordinates(meuse.utmintl)[1:3,]
             x       y
[1,] 272561.0 5654094
[2,] 272511.5 5654043
[3,] 272650.3 5654015

meuse.lonlatWGS84WGS84 <- spTransform(meuse.utm, CRS("+proj=lonlat +ellps=WGS84"))
meuse.lonlatWGS84intl  <- spTransform(meuse.utm, CRS("+proj=lonlat +ellps=intl"))
coordinates(meuse.lonlatWGS84WGS84)[1:3,]
             x        y
[1,] 5.759053 50.99238
[2,] 5.758380 50.99190
[3,] 5.760373 50.99171

coordinates(meuse.lonlatWGS84intl)[1:3,]
             x        y
[1,] 5.759053 50.99238
[2,] 5.758380 50.99190
[3,] 5.760373 50.99171

meuse.lonlatintlWGS84 <- spTransform(meuse.utmintl, CRS("+proj=lonlat 
+ellps=WGS84"))
meuse.lonlatintlintl  <- spTransform(meuse.utmintl, CRS("+proj=lonlat +ellps=intl"))
coordinates(meuse.lonlatintlWGS84)[1:3,]
             x        y
[1,] 5.759053 50.99238
[2,] 5.758380 50.99190
[3,] 5.760373 50.99171

coordinates(meuse.lonlatintlintl)[1:3,]
             x        y
[1,] 5.759053 50.99238
[2,] 5.758380 50.99190
[3,] 5.760373 50.99171

Test with Global Mapper

UTM ED50 272561.0 5654094 to lon,lat:
WGS84   5° 45' 27.5632" E	50° 59' 29.5996" N
ED50    5° 45' 32.5898" E	50° 59' 32.5665" N

UTM WGS84 272571.9 5653978 to lon,lat:
WGS84   5° 45' 32.5900" E	50° 59' 32.5621" N
ED50    5° 45' 37.6165" E	50° 59' 35.5289" N

Also, utmWGS84 to utmED50 is different in GlobalMapper

UTM WGS84  272571.9     5653978
UTM ED50   272662.989	5654181.171


Thanks,

Agus
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