I have received a shapefile with measurement points to be analyzed, but no matter how I try, I can't find how to convert to lat lon. I suppose it would be good to know the projection but when I look into the file (with R and summary()) it says "Is projected: NA" and "proj4string : [NA]".
One measurement-point I know is close to the border Peru-Chile has x,y = 354521, 7997417.8.
How can I find out how to convert this point (and many others) to lat lon? I tried to follow the instructions of similar questions here, but to no avail.