geoJSON and leaflet

Hi Benjamin,
What you get back from the jsonlite::fromJSON() call is a simplified list
with the data (including the geometry information) as a data frame in one
of the list slots. GeoJson is usually a character string. Therefore, if you
open your map in the browser and open the console (Ctrl + i) you will see
the error message: "Invalid GeoJson object".

I am no expert on geojson structure, but it seems that the data that you
request is not in standard format. I tried a few different ways of parsing
the data to a valid GeoJson string but did not have success. Maybe someone
else with more insight has some helpful ideas how to achieve this.

However, I found a workaround to get the polygons shown on the map using
library(sf) - see code below. Note, this only visualises the geometry
information only, so direct popup queries via "~" are not possible.

library(leaflet)
library(jsonlite)
library(sf)

url <- "
http://www.georisques.gouv.fr/api/v1/sis?rayon=1000&latlon=4.854899%2C%2045.763079&page=1&page_size=10
"

geojson <- jsonlite::fromJSON(url)

# convert coordinate arrays to matrices
geom = lapply(geojson$data$geom$coordinates, matrix, ncol = 2)
# create multipolygon from coordinate matrices
geom = st_cast(st_polygon(geom), "MULTIPOLYGON")

leaflet() %>%
  addTiles()%>%
  setView(lng = 4.854899, lat = 45.763079, zoom = 14) %>%
  addMarkers(lng = 4.872536, lat = 45.758321)%>%
  addPolygons(data = geom)

HTH,
Tim



On Tue, Jul 9, 2019 at 1:49 PM Benjamin Pauget <benjamin.pauget at tesora.fr>
wrote:

Hi,

I?m writting because I have some trouble with a geoJSON file and a leaflet.

I?m trying to display polygon on a leaflet map, but nothing append ?

I have no error message.

Do you have some advice/ideas?



Best regards





Here is my code :

library(leaflet)

library(jsonlite)

url <- "
http://www.georisques.gouv.fr/api/v1/sis?rayon=1000&latlon=4.854899%2C%2045.763079&page=1&page_size=10
"

geojson <- jsonlite::fromJSON(url)

leaflet() %>%

  addTiles()%>%

  setView(lng = 4.854899, lat = 45.763079, zoom = 14) %>%

  addMarkers(lng = 4.872536, lat = 45.758321)%>%

  addGeoJSON(geojson) # doesn?t work by using geojson$data or
geojson$data$geom









*Benjamin PAUGET*

Responsable R&D

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