I have some coordinated in SWEREF 99 TM which I cannot convert into WGS84 using the proj4 package in R.
temp <- data.frame (x = c(598223, 598812, 598824, 598232, 597614, 597629),
y = c(7095460, 7095426, 7094827, 7094227, 7094821, 7095433))
ptransform(temp,
src.proj = '+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs ',
dst.proj = '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs', silent=TRUE)
Note that the output is not equivalent to coordinates in Sweden - latitudes are equivalent to those near the equator.