Add polygon to map R leaflet

Question

I am trying to display a map with R using the rCharts package. I am starting simple and so I want to add a polygon to my map. But I have no clue how. Any ideas? addPolygon doesnt work.

map <- Leaflet$new()


map$tileLayer(provider = 'Stamen.TonerLite')

map$setView(c(48.1, 16.7), zoom = 10)
map$addPolygon(
  c(48.99831, 49.08815, 49.08815, 48.99831, 48.99831),
  c(13.42666, 13.42666, 13.56383, 13.56358, 13.42666),
  layerId=c("1"),
  options=opts,
  defaultOptions=opts)
map

Narcoma

"Doesn't work" how? Error message? Don't see it on the map? Is it there in the code? Do you mean the leafletR package? Or something else not from CRAN? Where? What version? – Biddy

I am using the "rCharts" package and I get the following error message: Error in envRefInferField(x, what, getClass(class(x)), selfEnv) : ‘addPolygon’ is not a valid field or method name for reference class “Leaflet” – Narcoma

What makes you think "addPolygon" would do anything? Did you read it somewhere? There's no such thing in the package... – Biddy

you are right! Do you have any idea what function i could use to add a polygon to my map? Would it maybe be easier to do that with the leaftletR package? My problem witht the leafletR package is, that I dont know how to implement the map in shiny once I made. – Narcoma

Answer 1

Add the polygon to your map by converting to geoJSON format, as in example 10 in the rCharts source code: https://github.com/ramnathv/rCharts/blob/master/inst/libraries/leaflet/examples/example10.R

Note how lat and long are different between the xy coords in the geoJSON and the setView. This here code gives me a blue box in the Czech Republic close to Germany.

xy = cbind(
  c(13.42666, 13.42666, 13.56383, 13.56358, 13.42666),
    c(48.99831, 49.08815, 49.08815, 48.99831, 48.99831)
    )

xyjson = RJSONIO::toJSON(xy)

jsonX = paste(
    '{"type":"FeatureCollection","features":[
        {"type":"Feature",
         "properties":{"region_id":1, "region_name":"My Region"},
         "geometry":{"type":"Polygon","coordinates": [ ',xyjson,' ]}}
       ]
      }')

polys = RJSONIO::fromJSON(jsonX)
map = Leaflet$new()
map$tileLayer(provider = 'Stamen.TonerLite')
map$setView(c(49.1,13.5), zoom = 8)
map$geoJson(polys)
map
# or print(map) from a script probably.

If you have more than one polygon, you need to create several structures of the {"type": "Feature", and comma-separate them within the square brackets of the "features" of the "FeatureCollection". I've re-indented things a bit to show the structure better. Its getting to the point where a templating system like the brew package is going to help you...

Biddy

Newbie question, but how then can I draw TWO polygons? (I'm actually going to be drawing hundreds, would love to be able add labels/popups/colours to the polygons too) – Andi

I suspect it might be easier to ask the package authors to add some functionality since this is pretty common usage - but I've edited a bit to show how to do it in principle. – Biddy