add backtransform_range() to coord_map

Author: clauswilke

R/coord-map.r

@@ -119,6 +119,11 @@ CoordMap <- ggproto("CoordMap", Coord,
     out
   },
 
+  backtransform_range = function(panel_params) {
+    # range is stored in data coordinates and doesn't have to be back-transformed
+    list(x = panel_params$x.range, y = panel_params$y.range)
+  },
+
   distance = function(x, y, panel_params) {
     max_dist <- dist_central_angle(panel_params$x.range, panel_params$y.range)
     dist_central_angle(x, y) / max_dist