12

I'm using Leaflet to transform some drawn polygons to GeoJSON and send them to a backend. But the GeoJSON objects generated by layer.toGeoJSON are like this:

{
 "type":"Feature",
 "properties":{},
 "geometry":{
    "type":"Polygon",
    "coordinates":[[[18.69873046875,51.481382896100975],[18.69873046875,51.890053935216926],[20.456542968749996,51.890053935216926],[20.456542968749996,51.481382896100975],[18.69873046875,51.481382896100975]]]
  }
 }

When I receive that GeoJSON object in the backend of my application (Django based) and create a GEOS object from it, epsg:4326 is assumed. Even when epsg:3857 is used for the map.

I know GeoJSON spec supports CRS definition, but I don't know how to include it in the GeoJSON object generated by toGeoJSON.

Any suggestion?

3 Answers 3

11

You can just set the crs field:

object.crs =  {
  "type": "name",
  "properties": {
    "name": "epsg:3857"
    }
  }

Note however that the coordinates you give in your example really are epsg:4326 coordinates, which is also what leaflet would output by default. I don't think you need a change here.

3
  • Thanks! You're right. For any reason, I was thinking about epsg:3857 as a not projected CRS, what obviously isn't. Those coords are 4326, of course. Silly me! Commented Dec 17, 2013 at 18:43
  • 9
    As this reply just got an upvote, note 4 years later that setting a crs is no longer part of the geojson standard. You should really consider working only in epsg:4326 all the time.
    – johanvdw
    Commented Oct 4, 2017 at 19:00
  • Thanks! So, this isn't the valid response anymore. Commented Oct 5, 2018 at 11:06
8

This is a link to the comment made by @johanvdw saying the CRS for all GeoJSON is epsg:4326 (WGS84) https://www.rfc-editor.org/rfc/rfc7946#section-4

0

I am not an expert but I would like to share what I did to tackle it. Since GeoJSON is basically a string, I added a string specifying the CRS (3857 in this example) manually. Might be useful to someone.

json = geo_df.to_json()
attr = grid_out.split(',', 1)
json_with_crs = attr[0] + ', "crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:EPSG::3857" } },' + attr[1]

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