在ggplot2中的地图上围绕点绘制具有特定半径的圆

时间:2015-12-09 15:47:20

标签: r ggplot2 gis geometry ggmap

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?

5 个答案:

答案 0 :(得分:15)

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。

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答案 1 :(得分:6)

好吧,正如referred posting已经建议的那样 - 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可以以米为单位指定:

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

将其转换回来并使用geom_path

将其添加到地块中
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)) 

enter image description here

答案 2 :(得分:4)

计算给定纬度和经度的km的距离并不是非常直接的;例如,1度纬度/长度在赤道处的距离大于在极点处的距离。如果您想要一个简单的解决方法,您可以考虑准确性,您可以尝试:

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)) + 
  geom_point(aes(x = longitude, y = latitude), data = data, size = 20, shape = 1,  color = "#ff0000")

enter image description here

您需要调整第二个size中的geom_point参数,以便更接近您想要的内容。我希望有所帮助!

答案 3 :(得分:1)

准确的解决方案是使用geosphere :: destPoint()函数。无需切换投影即可实现。

定义函数以确定在一个点附近具有特定半径的360个点:

library(dplyr)
library(geosphere)

fn_circle <- function(id1, lon1, lat1, radius){ 
   data.frame(ID = id1, degree = 1:360) %>%
      rowwise() %>%
      mutate(lon = destPoint(c(lon1, lat1), degree, radius)[1]) %>%
      mutate(lat = destPoint(c(lon1, lat1), degree, radius)[2]) 
}

将函数应用于data的每一行并转换为data.frame:

circle <- apply(data, 1, function(x) fn_circle(x[1], x[2], x[3], 450))
circle <- do.call(rbind, circle)

然后可以通过以下方式轻松获得地图:

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)) +
   geom_polygon(data = circle, aes(lon, lat, group = ID), color = "red", alpha = 0)

enter image description here

答案 4 :(得分:0)

使用sf软件包中的st_buffer()的解决方案。

library(ggmap)
library(ggplot2)
library(sf)

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

将data.frame转换为sf对象:

points_sf <- sf::st_as_sf(data, coords = c("longitude", "latitude"), crs = 4326)

在此示例中,我们使用UTM区域20,其中包含岛屿的坐标:

data_sf_utm <- sf::st_transform(points_sf, "+proj=utm +zone=20")

现在我们可以将点缓冲450米:

circle <- sf::st_buffer(data_sf_utm, dist = 450)

ggmap似乎与geom_sf有关。将Inherit.aes设置为FALSE会返回所需的映射。

island <- ggmap::get_map(location = c(lon = -63.247593, lat = 17.631598), zoom = 14, maptype = "satellite")

ggmap(island, extent = "panel", legend = "bottomright") + 
  geom_sf(data = points_sf, color = "red", inherit.aes = FALSE) +
  geom_sf(data = circle, color = "red", alpha = 0, inherit.aes = FALSE)

reprex package(v0.3.0)于2020-10-11创建