Converting UTM coordinates to Lat/Long in R

Question

I am trying to convert UTM coordinates (Easting and Northing) to Lat/Long using R. A sample of my data is as follows:

dx	dy
-17.551	17.062
-4.947	2.336
-17.265	3.956
-12.157	-2.043

Here is my code:

    library(dplyr)
    library(ggmap)
    library(maps)
    library(rgdal)
    library(ggplot2)
    
    east<-as.numeric(ddata$dy)
    north<-as.numeric(ddata$dx)
    utm <- SpatialPoints(cbind(east,north), 
                 proj4string=CRS("+proj=utm +zone=59 +datume=WGS84 "))
    spTransform(utm, CRS("+proj=longlat +datum=WGS84"))

However, I'm not getting correct lat/long values, as the data is collected from New Zealand so the latitude, longitude values must be from this location. How can I correct this code to generate the right values of lat and long?

Here is a link to my data: https://drive.google.com/file/d/1X8pPFxV8ZBl1gAWOeYASG0BsnryovpyE/view?usp=sharing

Any help in this regard will be highly appreciated.

Welcome to Stack Overflow. Please paste sample data in the question; use dput(ddata) or use dput(head(ddata)) so that the question becomes reproducible to allow answers to be verified. minimal reproducible example provides useful guidance. — Peter
Could you include the packages you are using in the question? — Peter
Can you include the reference from which you collected the data? Are the Eastings and Northings defined? Check your assignments, typically longitude is the equated with the x-axis i.e. east <- as.numeric(ddata$dx). — Peter
Is there metadata for the variables in your data? i.e. an explanation of what the variables represent. Just checked definition of UTM and it seems as if latitude in the southern hemisphere is defined with positive values, so previous comment about negative latitude values withdrawn. Do you know what the x and y variables in the original dataset represent? — Peter

Peter Peter · Accepted Answer · 2021-04-24T16:22:46

This may help...

Data is the first 6 rows and columns from the link provided in the question. Have used x variable as longitude and y as latitude. A search on the internet revealed a crs for New Zealand to be 2193: New Zealand Transverse Mercator which at least puts the co-ordinates in New Zealand. But you'd need to confirm that. The co-ordinates seem to be very close to each other so all points overlap at the scale plotted - I've not experimented with this.

https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/projections/new-zealand-transverse-mercator-2000


library(sf)
library(tmap)

df_sf <- st_as_sf(x = df,                         
                  coords = c("x", "y"),
                  crs =     2193)

data("World")
nz <-  World[World$name == "New Zealand", ]

tm_shape(nz, projection = "wgs84") +
  tm_polygons()+
  tm_grid()+
  tm_shape(df_sf, projection = "wgs84")+
  tm_dots("id", size = 0.5)

To convert UTM x, y coordinates into longitude and latitude

library(proj4)

# Find the projection proj4 description of the coordinate reference system (espg 2193)
#  I've used information from this link:
# https://spatialreference.org/ref/epsg/nzgd2000-new-zealand-transverse-mercator-2000/proj4/

proj4 <- "+proj=tmerc +lat_0=0 +lon_0=173 +k=0.9996 +x_0=1600000 +y_0=10000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs "

# From the source data extract the x, y coordinates of the UTM
x_y <- df[, 1:2]

# Transform the data
lon_lat <- project(x_y, proj4, inverse = TRUE)

# convert to a data frame
data.frame(lon = lon_lat$x, lat = lon_lat$y)

#>        lon       lat
#> 1 132.3681 -71.33355
#> 2 132.3685 -71.33371
#> 3 132.3686 -71.33375
#> 4 132.3690 -71.33391
#> 5 132.3692 -71.33402
#> 6 132.3689 -71.33392

data

df <- structure(list(id = 423:428, x = c(1455320.99774103, 1455303.44574159, 
                                         1455298.49781114, 1455281.23215399, 1455269.07477818, 1455280.83403596
), y = c(5131693.29609067, 5131710.35870728, 5131712.69526321, 
         5131716.65168218, 5131714.60800342, 5131734.86699543), date = c("2019-03-12 00:02:00", 
                                                                         "2019-03-12 00:04:49", "2019-03-12 00:07:37", "2019-03-12 00:10:24", 
                                                                         "2019-03-12 00:13:19", "2019-03-12 00:16:06"), dx = c(-17.5519994448405, 
                                                                                                                               -4.94793045334518, -17.2656571443658, -12.1573758164886, 11.7592577852774, 
                                                                                                                               16.6252572031226), dy = c(17.0626166081056, 2.33655592985451, 
                                                                                                                                                         3.95641897153109, -2.04367875494063, 20.2589920070022, -29.7507258579135
                                                                                                                               )), class = "data.frame", row.names = c(NA, 6L))

^{Created on 2021-04-28 by the reprex package (v2.0.0)}

Converting UTM coordinates to Lat/Long in R

1 Answers