Converting projected coordinates into decimals-CodePudding

I have the following data set with coordinates in decimals:

ID     Longitude  Latitude
 1     -93.2552   58.0879
 1     -93.2558   58.0876
 1     -93.2555   58.0873

For a previous project, I projected the coordinates using the following code:

  library(rgdal)
  coordinates(data) <- c("longitude", "latitude")
  proj4string(data) <- CRS(" init=epsg:4326")
  data <- spTransform(data, CRS(" init=epsg:5321"))
  data<-as.data.frame(data)

Now, I need to re-use the original decimal coordinates. Could anyone tell me how to convert the projected coordinates back into decimal?

CodePudding user response：

You can repeat your previous steps, but switch the projections in proj4string and spTransform.

library(rgdal)

data_old <- data
coordinates(data_old) <- c("Longitude", "Latitude")
proj4string(data_old) <- CRS(" init=epsg:4326")
data_old <- spTransform(data_old, CRS(" init=epsg:5321"))
data_old <- as.data.frame(data_old)

#    ID Longitude Latitude
# 1  1  451077.2  7117021
# 2  1  451037.6  7116991
# 3  1  451051.2  7116956

Then, you can just switch the projection in your code to revert back to the original coordinates.

data_new <- data_old
coordinates(data_new) <- c("Longitude", "Latitude")
proj4string(data_new) <- CRS(" init=epsg:5321")
data_new <- spTransform(data_new, CRS(" init=epsg:4326"))
data_new <- as.data.frame(data_new)

Output

  ID Longitude Latitude
1  1  -93.2552  58.0879
2  1  -93.2558  58.0876
3  1  -93.2555  58.0873

Another option using tidyverse and sf could be:

library(tidyverse)
library(sf)

data_old %>%
  st_as_sf(coords = c("Longitude", "Latitude"), dim = "XY") %>%
  st_set_crs(5321) %>%
  st_transform(4326) %>%
  as.data.frame() %>%
  extract(geometry,
          c('Longitude', 'Latitude'),
          '\\((.*), (.*)\\)',
          convert = TRUE)

Data

data <-
  structure(
    list(
      ID = c(1, 1, 1),
      Longitude = c(-93.2552,-93.2558,-93.2555),
      Latitude = c(58.0879, 58.0876, 58.0873)
    ),
    class = "data.frame",
    row.names = c(NA,-3L)
  )