R - Problems with converting UTM coordinates with the rgdal package

Question

I have been given the task to convert a large set of UTM coordinates (Zone 33) to lat-long (WGS84) coordinates. The positions are supposed to be located near the Norwegian border. I have tried to convert the coordinates in R using the rgdal package

#extracting some examples from data set

lat <- c(7790281, 7726438, 7266202, 7259480, 7271802)
long <- c(1053817, 1054025, 451754, 475228, 462235)
df <- data.frame(lat, long)

#converting from UTM33 to WGS84

library(rgdal)
tmp <- data.frame(coords.x = df$lat, coords.y = df$long)
coordinates(tmp) <-c("coords.x","coords.y")
proj4string(tmp) <- CRS("+proj=utm +zone=33 ellps=WGS84") #UTM zone 33
CRS.new <- CRS("+init=epsg:4326") # WGS84
coords <- spTransform(tmp,CRS.new)

#making a dataframe out of coordinates
coords <- data.frame(lat=coords@coords[,1], long=coords@coords[,2])

This yields

       lat     long
1 69.19936 5.840162
2 68.92219 5.857922
3 66.55129 2.585804
4 66.52160 2.721701
5 66.58242 2.644578

However, when transforming the coordinates with an online converting tool (http://www.rcn.montana.edu/resources/converter.aspx) I get the following different results

  lat.corr long.corr
1 69.63112  29.37223
2 69.07562  29.00514
3 65.51455  13.95675
4 65.45688  14.46554
5 65.56618  14.18178

When plotting both data sets in the same map, one can clearly see that the points converted with rgdal are misplaced.

Map

If have tried to understand what the problem is, but after many hours of consideration and research, I was still unable to find it. Some help to find what the problem is would be much obliged!

Edit: it may have something to do with the Easting coordinates crossing the UTM zone borders. Could it be that rgdal has problems coping with that?

Answer 1

I guess you mixed latitude and longitude in

tmp <- data.frame(coords.x = df$lat, coords.y = df$long)

It should be :

tmp <- data.frame(coords.x = df$lon, coords.y = df$lat)

And you get :

> (coords <- data.frame(lon=coords@coords[,1], lat=coords@coords[,2]))
   lon     lat
1 29.37172 69.63114
2 29.00472 69.07564
3 13.95675 65.51455
4 14.46554 65.45688
5 14.18178 65.56618