如何将 API 响应转换为 R 中的多边形对象? R 中的 Graphhopper API - 等时线

How do I convert an API response to a Polygon object in R? Graphhopper API in R - Isochrones

我是 API 和 R 的新手,我想知道如何使用这个 GraphHopper API。(https://graphhopper.com/api/1/docs/isochrone/https://graphhopper.com/api/1/docs/isochrone/) 上面的页面是这样的:

curl "https://graphhopper.com/api/1/isochrone?point=51.131108,12.414551&key=[YOUR_KEY]"

有没有办法将响应转换为多边形对象?

到目前为止我到了这里,但我不知道如何将请求转换为多边形:

library(httr)
library(jsonlite)

a = GET("https://graphhopper.com/api/1/isochrone?point=51.131108,12.414551&key=KEY")

class(a)

a$status_code

这有效..

library(RJSONIO)
library(sp)
library(leaflet)

## GraphHopper API
# https://graphhopper.com/api/1/docs/isochrone/

#Request
a <-fromJSON("https://graphhopper.com/api/1/isochrone?point=51.131108,12.414551&key=[GET YOUR OWN KEY]")

#Response
x = a$polygons$geometry$coordinates

#Response Manipulation
x = data.frame(unlist(x))
m = nrow(x)/2
x1 = x[1:m,1]
x2 = x[(1+m):nrow(x),1]
x0 = data.frame(cbind(x1,x2))

#Polygon plotting on Leaflet
p = Polygon(coords = x0)

leaflet()%>%
  addTiles()%>%
  addPolygons(data = p)