在ggplot2中的地图上围绕点绘制具有特定半径的圆

我有一张地图,上面画着8个点:

library(ggplot2)
library(ggmap)
data = data.frame(
    ID = as.numeric(c(1:8)),
    longitude = as.numeric(c(-63.27462, -63.26499, -63.25658, -63.2519, -63.2311, -63.2175, -63.23623, -63.25958)),
    latitude = as.numeric(c(17.6328, 17.64614, 17.64755, 17.64632, 17.64888, 17.63113, 17.61252, 17.62463))
)

island = get_map(location = c(lon = -63.247593, lat = 17.631598), zoom = 13, maptype = "satellite")
islandMap = ggmap(island, extent = "panel", legend = "bottomright")
RL = geom_point(aes(x = longitude, y = latitude), data = data, color = "#ff0000")
islandMap + RL + scale_x_continuous(limits = c(-63.280, -63.21), expand = c(0, 0)) + scale_y_continuous(limits = c(17.605, 17.66), expand = c(0, 0))

现在我想围绕8个绘制位置绘制一个圆圈.圆的半径必须为450米.

这就是我的意思,但随后使用ggplot:https://gis.stackexchange.com/questions/119736/ggmap-create-circle-symbol-where-radius-represents-distance-miles-or-km

我怎样才能做到这一点？

如果你只在地球的一个小区域工作,这里是近似值.每个纬度都代表40075/360公里.每个经度表示(40075/360)*cos(纬度)千米.有了这个,我们可以计算大约一个数据框,包括圆上的所有点,知道圆心和半径.

library(ggplot2)
library(ggmap)
data = data.frame(
    ID = as.numeric(c(1:8)),
    longitude = as.numeric(c(-63.27462, -63.26499, -63.25658, -63.2519, -63.2311, -63.2175, -63.23623, -63.25958)),
    latitude = as.numeric(c(17.6328, 17.64614, 17.64755, 17.64632, 17.64888, 17.63113, 17.61252, 17.62463))
)

#################################################################################
# create circles data frame from the centers data frame
make_circles <- function(centers, radius, nPoints = 100){
    # centers: the data frame of centers with ID
    # radius: radius measured in kilometer
    #
    meanLat <- mean(centers$latitude)
    # length per longitude changes with lattitude, so need correction
    radiusLon <- radius /111 / cos(meanLat/57.3) 
    radiusLat <- radius / 111
    circleDF <- data.frame(ID = rep(centers$ID, each = nPoints))
    angle <- seq(0,2*pi,length.out = nPoints)

    circleDF$lon <- unlist(lapply(centers$longitude, function(x) x + radiusLon * cos(angle)))
    circleDF$lat <- unlist(lapply(centers$latitude, function(x) x + radiusLat * sin(angle)))
    return(circleDF)
}

# here is the data frame for all circles
myCircles <- make_circles(data, 0.45)
##################################################################################


island = get_map(location = c(lon = -63.247593, lat = 17.631598), zoom = 13, maptype = "satellite")
islandMap = ggmap(island, extent = "panel", legend = "bottomright")
RL = geom_point(aes(x = longitude, y = latitude), data = data, color = "#ff0000")
islandMap + RL + 
    scale_x_continuous(limits = c(-63.280, -63.21), expand = c(0, 0)) + 
    scale_y_continuous(limits = c(17.605, 17.66), expand = c(0, 0)) +
    ########### add circles
    geom_polygon(data = myCircles, aes(lon, lat, group = ID), color = "red", alpha = 0)

好吧,正如推荐的帖子已经暗示的那样 - 切换到以米为单位的投影,然后返回:

library(rgeos)
library(sp)
d <- SpatialPointsDataFrame(coords = data[, -1], 
                            data = data, 
                            proj4string = CRS("+init=epsg:4326"))
d_mrc <- spTransform(d, CRS("+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs"))

现在,width可以用米来指定:

d_mrc_bff_mrc <- gBuffer(d_mrc, byid = TRUE, width = 450)

将其转换回来并使用geom_path以下方法将其添加到绘图中:

d_mrc_bff <- spTransform(d_mrc_bff_mrc, CRS("+init=epsg:4326"))
d_mrc_bff_fort <- fortify(d_mrc_bff)
islandMap + 
  RL + 
  geom_path(data=d_mrc_bff_fort, aes(long, lat, group=group), color="red") + 
  scale_x_continuous(limits = c(-63.280, -63.21), expand = c(0, 0)) + 
  scale_y_continuous(limits = c(17.605, 17.66), expand = c(0, 0))