Converts between longitude conventions

Converts longitude from [0, 360) to [-180, 180) and vice versa.

ConvertLongitude(lon, group = NULL, from = NULL)

Arguments

lon

numeric vector of longitude

group

optional vector of groups (the same length as longitude) that will be split on the edges (see examples)

from

optionally explicitly say from which convention to convert

Value

If group is missing, a numeric vector the same length of lon. Else, a list with vectors lon and group.

Examples

library(ggplot2)
library(data.table)
data(geopotential)

ggplot(geopotential[date == date[1]], aes(lon, lat, z = gh)) +
    geom_contour(color = "black") +
    geom_contour(aes(x = ConvertLongitude(lon)))


map <- setDT(map_data("world"))
map[, c("lon", "group2") := ConvertLongitude(long, group, from = 180)]
#>             long      lat group  order  region subregion       lon group2
#>            <num>    <num> <num>  <int>  <char>    <char>     <num> <char>
#>     1: -69.89912 12.45200     1      1   Aruba      <NA> 290.10088    1_2
#>     2: -69.89571 12.42300     1      2   Aruba      <NA> 290.10429    1_2
#>     3: -69.94219 12.43853     1      3   Aruba      <NA> 290.05781    1_2
#>     4: -70.00415 12.50049     1      4   Aruba      <NA> 289.99585    1_2
#>     5: -70.06612 12.54697     1      5   Aruba      <NA> 289.93388    1_2
#>    ---                                                                   
#> 99334:  12.43838 41.90620  1627 100960 Vatican   enclave  12.43838 1627_2
#> 99335:  12.43057 41.90547  1627 100961 Vatican   enclave  12.43057 1627_2
#> 99336:  12.42754 41.90073  1627 100962 Vatican   enclave  12.42754 1627_2
#> 99337:  12.43057 41.89756  1627 100963 Vatican   enclave  12.43057 1627_2
#> 99338:  12.43916 41.89839  1627 100964 Vatican   enclave  12.43916 1627_2

ggplot(map, aes(lon, lat, group = group2)) +
    geom_path()