How to flip y axis in geom_sf()?

Question

Trying to combine a geom_sf() with some other geoms. I need to reverse the y-axis for the plot to appear correctly. However, geom_sf() seems to ignore scale_y_reverse().

Example:

# install the dev version of ggplot2
devtools::install_github("tidyverse/ggplot2")

library(ggplot2)
library(sf)
library(rgeos)
library(sp)

# make triangle
tmpdf <- data.frame(id = 1,
                    geom = c("LINESTRING(10 10,-10 10,0 0,10 10)"), stringsAsFactors = F)


# read WKT polygons into 'sp' SpatialPolygons object
tmpdf$spgeom <- lapply(tmpdf$geom, FUN = function(x) readWKT(x))

# extract coordinates from the linestring (there has got to be a better way to do this...)
test <- tmpdf[1,"spgeom"]
test2 <- sapply(test, FUN=function(x) x@lines)
test3 <- sapply(test2, FUN=function(x) x@Lines)
test4 <- lapply(test3, FUN=function(x) x@coords)

# plot the sp coordinates
ggplot() + 
  geom_point(data=data.frame(test4[[1]]), aes(x,y), color="blue") + 
  geom_path(data=data.frame(test4[[1]]), aes(x=x, y=y), color="blue") + 
  coord_fixed()

# make an 'sf' sfc_POLYGON object
tmpdf$sfgeom <- st_as_sfc(tmpdf$geom) 

## plot both together, they overlap
ggplot() + 
  geom_point(data=data.frame(test4[[1]]), aes(x,y), color="blue") + 
  geom_path(data=data.frame(test4[[1]]), aes(x=x, y=y), color="blue") + 
  coord_fixed() +  
  geom_sf(data=tmpdf, aes(geometry=sfgeom), color="red")

plot outputs with warning:

Coordinate system already present. Adding new coordinate system, which will replace the existing one.

## plot with scale reverse, and everything but the geom_sf flips.
ggplot() + 
  geom_point(data=data.frame(test4[[1]]), aes(x,y), color="blue") + 
  geom_path(data=data.frame(test4[[1]]), aes(x=x, y=y), color="blue") + 
  coord_fixed() +  
  geom_sf(data=tmpdf, aes(geometry=sfgeom), color="red") + 
  scale_y_reverse()

plot outputs with warning:

Coordinate system already present. Adding new coordinate system, which will replace the existing one.

Suggestions for getting the geom_sf y coordinates reversed?

I tried this:

coord_sf(ylim=-(range(st_coordinates(tmpdf$sfgeom)[,"Y"])))

and all that did was change the axis, not the actual geoms.

Answer 1

Aha! Here's a workaround:

## get the geom coordinates as data.frame
geomdf <- st_coordinates(tmpdf$sfgeom)

## reverse Y coords
geomdf[,"Y"] <- geomdf[,"Y"]*-1

## re-create geom
tmpdf$sfgeom2 <- st_as_sfc(st_as_text(st_linestring(geomdf)))

## plot the reversed y-coordinate geom:
ggplot() + 
  geom_point(data=data.frame(test4[[1]]), aes(x,y), color="blue") + 
  geom_path(data=data.frame(test4[[1]]), aes(x=x, y=y), color="blue") + 
  coord_fixed() +  
  geom_sf(data=tmpdf, aes(geometry=sfgeom2), color="red") + 
  scale_y_reverse()