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

Question

I am new to API's and R, and I was wondering how to use this GraphHopper API.(https://graphhopper.com/api/1/docs/isochrone/https://graphhopper.com/api/1/docs/isochrone/) At the page above there is this:

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

Is there a way to make to convert the response to a polygon object?

So far i got here, but I don't know how to convert the request to a Polygon:

library(httr)
library(jsonlite)

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

class(a)

a$status_code

Answer 1

This worked..

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)