How to rotate a map made with ggplot2 and include a north arrow?-CodePudding

I am making a map in ggplot2 and am trying to rotate the map slightly. Following

Changing the CRS to the oblique mercator yields a rotated image but no north arrow:

crs_string = " proj=omerc  lat_0=39.95276  lonc=-75.16340,  alpha=0  k_0=1  datum=WGS84  units=m  no_defs  gamma=-11"

ggplot() 
  geom_sf(data = places,fill=NA,color='black',linewidth = 1) 
  geom_sf(data = roads[roads$RTTYP=="S",],color="black",linewidth=1) 
  north(data = places,
        location = 'topleft',
        scale = .1,
        symbol = 11) 
  coord_sf(datum = NA, crs = crs_string)

Finally, changing the data projection for the north arrow brings the north arrow back, but yields a north arrow that points directly "up" rather than to true north.

ggplot() 
  geom_sf(data = places,fill=NA,color='black',linewidth = 1) 
  geom_sf(data = roads[roads$RTTYP=="S",],color="black",linewidth=1) 
  north(data = st_transform(places,crs = " proj=omerc  lat_0=39.95276  lonc=-75.16340,  alpha=10  k_0=1  datum=WGS84  units=m  no_defs  gamma=0"),
        location = 'topleft',
        scale = .1,
        symbol = 11) 
  coord_sf(datum = NA, crs = crs_string)

CodePudding user response：

Okay, not with ggsn but with ggspatial I was able to get this to work:

library(sf)
library(ggplot2)
library(tigris)
library(ggspatial)

places<-places(state = 42)
places<-places[places$NAME=="Philadelphia",]
roads<-roads(state = "42",county = "101")

crs_string = " proj=omerc  lat_0=39.95276  lonc=-75.16340,  alpha=0  k_0=1  datum=WGS84  units=m  no_defs  gamma=-11"

ggplot() 
  geom_sf(data = places,fill=NA,color='black',linewidth = 1) 
  geom_sf(data = roads[roads$RTTYP=="S",],color="black",linewidth=1) 
  annotation_north_arrow(which_north = "true",style = north_arrow_minimal(),location ="tl") 
  coord_sf(datum = NA, crs = crs_string)