# Wrong northing value: standardizing with a correction by 10 000 000 meters

I'm trying to draw points on a map and I have a problem using the projections. I have no problem getting points from `longlat` to `UTM`. But it seems that there is a problem when specifying UTM zone 15M and then try to plot them. I figure out that there is a difference of `10 000 000 meters` between the 2 coordinates that I had. Why is that?

``````library(sp)
library(mapview)

gps.pt = data.frame(lon = -90.22139,
lat = -0.6893730)
lonlat= sp::SpatialPoints(gps.pt, proj4string=CRS("+proj=longlat +datum=WGS84"))
spgeo <- sp::spTransform(lonlat, CRS("+proj=utm +zone=15M +datum=WGS84"))
# OK!
mapview::mapView(spgeo)

# Wrong map (the easting and northing values were collected from [memento] on an Android smartphone)
gps.pt2 = data.frame(easting = 809289.5,
northing = 9923713)
spgeo2 = sp::SpatialPoints(gps.pt2, proj4string=CRS("+proj=utm +zone=15M +datum=WGS84"))
mapview::mapView(spgeo2)

# Now OK!
gps.pt3 = data.frame(easting = 809289.5,
northing = 9923713-10000000)
spgeo3 = sp::SpatialPoints(gps.pt3, proj4string=CRS("+proj=utm +zone=15M +datum=WGS84"))
mapview::mapView(spgeo3)
``````

Do I actually have to subtract 10 000 000 meters or I've just specified my CRS wrong? When should I apply a 10 000 000 meters correction?

• try `proj4string=CRS("+proj=utm +zone=15M +south +datum=WGS84")` to tell the projection you're in the southern hemisphere. Sep 17, 2019 at 12:34
• Worked beautifully! Thanks a lot! I haven't found a "cheatsheet" for all the CRS things we can put inside a CRS. Do you have something like that? Sep 17, 2019 at 13:30
• My goto reference is epsg.io. I am not aware of a cheatsheet as such. Sep 17, 2019 at 13:38
• For more general doc on the proj library see, proj.org. "M" is the latitude band, 0 to -8°, but I'm not sure that the proj library uses the latitude band to determine if the zone needs the +10million false northing. Thus, the +south parameter. Sep 17, 2019 at 16:32
• I think it's ignored, sf strips it but rgdal::CRSargs does not: sf::st_crs("+proj=utm +zone=15M +datum=WGS84") Sep 17, 2019 at 18:25