ggplot_scalebar

gistfile1.txt

From: 

https://stackoverflow.com/questions/34416892/how-to-add-a-scale-bar-in-ggplot-map

library(maps)
library(maptools)
library(ggplot2)
library(grid)

#
# Result #
#--------#
# Return a list whose elements are :
#   - rectangle : a data.frame containing the coordinates to draw the first rectangle ;
#   - rectangle2 : a data.frame containing the coordinates to draw the second rectangle ;
#   - legend : a data.frame containing the coordinates of the legend texts, and the texts as well.
#
# Arguments : #
#-------------#
# lon, lat : longitude and latitude of the bottom left point of the first rectangle to draw ;
# distanceLon : length of each rectangle ;
# distanceLat : width of each rectangle ;
# distanceLegend : distance between rectangles and legend texts ;
# dist.units : units of distance "km" (kilometers) (default), "nm" (nautical miles), "mi" (statute miles).
createScaleBar <- function(lon,lat,distanceLon,distanceLat,distanceLegend, dist.units = "km"){
  # First rectangle
  bottomRight <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon, dist.units = dist.units, model = "WGS84")

  topLeft <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLat, dist.units = dist.units, model = "WGS84")
  rectangle <- cbind(lon=c(lon, lon, bottomRight[1,"long"], bottomRight[1,"long"], lon),
                     lat = c(lat, topLeft[1,"lat"], topLeft[1,"lat"],lat, lat))
  rectangle <- data.frame(rectangle, stringsAsFactors = FALSE)

  # Second rectangle t right of the first rectangle
  bottomRight2 <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon*2, dist.units = dist.units, model = "WGS84")
  rectangle2 <- cbind(lon = c(bottomRight[1,"long"], bottomRight[1,"long"], bottomRight2[1,"long"], bottomRight2[1,"long"], bottomRight[1,"long"]),
                      lat=c(lat, topLeft[1,"lat"], topLeft[1,"lat"], lat, lat))
  rectangle2 <- data.frame(rectangle2, stringsAsFactors = FALSE)

  # Now let's deal with the text
  onTop <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLegend, dist.units = dist.units, model = "WGS84")
  onTop2 <- onTop3 <- onTop
  onTop2[1,"long"] <- bottomRight[1,"long"]
  onTop3[1,"long"] <- bottomRight2[1,"long"]

  legend <- rbind(onTop, onTop2, onTop3)
  legend <- data.frame(cbind(legend, text = c(0, distanceLon, distanceLon*2)), stringsAsFactors = FALSE, row.names = NULL)
  return(list(rectangle = rectangle, rectangle2 = rectangle2, legend = legend))
}