ST_AsGeoJSON doesn't export the CRS of multiple geometry columns

[tobwen]

summary

ST_AsGeoJSON only uses the first geometry column to create the feature's geometry. The other geometry columns get stored in properties. But here, the CRS is missing. It's not in GeoJSON specs, but it might be useful to reconstruct the geometry.

example

SELECT
    ST_AsGeoJSON(data.*)
FROM
    (SELECT
        1 AS id,
        ST_Transform(geom, 3035) geom,
        ST_Transform(geom, 25832) geom
    FROM
        ST_SetSRID(ST_MakePoint(7, 51), 4326) geom
    ) data;

result

{
  "type":"Feature",
  "geometry":{
    "type":"Point",
    "crs":{
      "type":"name",
      "properties":{
        "name":"EPSG:3035"
      }
    },
    "coordinates":[
      4110471.051819585,
      3103060.820290524
    ]
  },
  "properties":{
    "id":1,
    "geom":{
      "type":"Point",
      "coordinates":[
        359666.70366028673,
        5651728.682548149
      ]
    }
  }
}

nice to have

{
  "type":"Feature",
  "geometry":{
    "type":"Point",
    "crs":{
      "type":"name",
      "properties":{
        "name":"EPSG:3035"
      }
    },
    "coordinates":[
      4110471.051819585,
      3103060.820290524
    ]
  },
  "properties":{
    "id":1,
    "geom":{
      "crs":{
        "type":"name",
        "properties":{
          "name":"EPSG:25832"
        }
      },
      "type":"Point",
      "coordinates":[
        359666.70366028673,
        5651728.682548149
      ]
    }
  }
}

[Paul Ramsey <pramsey@…>]

In a9382ae/git:

Include srs in GeoJSON where it exists in spatial_ref_sys, closes #4799