使用ggmap创建正交贴图

在下面的脚本中,我读了许多点对并在地图上绘制线条.我正在使用ggmap从谷歌中提取地图来绘制这条线:

source('./library/latlong2state.R')

library(maps)
library(mapproj)
library(mapdata)
library(geosphere)
library(ggmap)

fileName = "_CanadaData/CanadaHospitalComplete.csv"

getLineColor <- function(val) {
  pal <- colorRampPalette(lineColours)
  colors <- pal(80)
  val.log <- log(val)

  if (val > 50) {
    col <- colors[80]
  } else {
    colindex <- max(1, round( 80 * val / 50))
    col <- colors[colindex]
  }
  return(col)
}

# Load the data
location <- read.csv(fileName, stringsAsFactors=FALSE)

# Omit locations that are not on the map of focus (not needed for city maps unless they are on a border)
location$state <- latlong2state(data.frame(location$lng, location$lat))
location$nearstate <- latlong2state(data.frame(location$lngnear, location$latnear))
location <- na.omit(location)

createMap <- function(bbox, thedata, mapzoom=3, linesize=0.6, pointsize=2) {
  basemap <- get_map(location=bbox, zoom=mapzoom, source='google', maptype="roadmap", color="color")
  ggmap(basemap) + geom_segment(aes(x=lng, xend=lngnear, y=lat, yend=latnear, color=dist_miles), size=0.6, data=thedata) + geom_point(aes(x=lngnear, y=latnear), size=2, color="#000000", border="black", data=thedata) + scale_color_gradient(low="blue", high="red", limits=c(0, max(thedata$dist_miles))) + coord_map("orthographic")
}

# Country bounding box c(left, bottom, right, top)
canada <- c(-140.920514, 42.016722, -52.524864, 83.2911)
createMap(canada, location)

不幸的是,由于加拿大的北纬度,这会导致地图顶部的距离大幅度扭曲:

这可以通过切换到正交图来轻松修复,我可以通过projection=mapprojection(orthographic)在createMap函数中添加来更改线条绘制方式的投影,但我无法更改从Google获得的地图图像的投影 - 它被卡在Web Mercator投影.有没有办法使用ggmap来做到这一点,还是我必须尝试不同的包？如果是这样,你推荐什么？