How to change map projection from pacific to Atlantic centered?

Question

library(sf)
library(tidyverse)

I have an sf object with

geometry type:point

projected over pacific

bbox: xmin: 0 ymin: -78 xmax: 359 ymax: 0 (WGS 84)

I want to re-project the sf object to Atlantic centered (-180,180) from pacific view (0,360). I found in sf package a function that allows to go from Atlantic to Pacific view (i.e.) st_shift_longitude(x). But what I want is the opposite ...

Help? Thanks

Answer 1

Tough to tell for sure without some hint at what the data looks like, but here's one way to do it:

I'm assuming the original sf object of points doesn't have a crs set, since 0-360 for longitude is unusual. The code below makes up some data points using -78-0 for latitude & 0-360 for longitude. A (somewhat unusual) crs of "+proj=longlat +ellps=WGS84 +pm=-360 +datum=WGS84 +no_defs" is set, and then transformed to the usual 4326 for lon/lat data.

library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
library(tidyverse)

set.seed(42)  # for reporducibility
points <- tibble(x = sample(0:359, size = 20, replace = T),
                 y = sample(-78:0, size = 20, replace = T)) %>%
  st_as_sf(coords = c("x", "y"), remove = F)

# Set a crs that understands 0-360 longitude
points <- st_set_crs(points, "+proj=longlat +ellps=WGS84 +pm=-360 +datum=WGS84 +no_defs")

# reproject to epsg 4326, the usual lon/lat crs
points_4326 <- points %>% st_transform(4326)

mapview::mapview(points_4326)

Head of the sample data showing both old (0-360) longitude, and new (-180 to 180) longitude:

> head(points_4326)
Simple feature collection with 6 features and 2 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: -166 ymin: -66 xmax: 88 ymax: -5
Geodetic CRS:  WGS 84
# A tibble: 6 × 3
      x     y    geometry
  <int> <int> <POINT [°]>
1   240   -66  (-120 -66)
2    23   -66    (23 -66)
3    46    -5     (46 -5)
4    88   -10    (88 -10)
5    17   -61    (17 -61)
6   194   -13  (-166 -13)

^{Created on 2022-04-19 by the reprex package (v2.0.1)}