reproject

This module provides operators to reproject GeoJSON objects between coordinate reference systems.

reprojectGeoJson

Signature

reprojectGeoJson (geoJson, target)

Description

Reprojects a GeoJSON object in place to the specified target coordinate reference system.

The source CRS is automatically extracted from the root GeoJSON object using extractGeoJsonCRS. When no CRS is declared, WGS84 is assumed.

The whole GeoJSON document is expected to use this single root CRS. Nested CRS declarations are not supported by validateGeoJson and should be rejected before reprojection.

All geometry types, Feature, FeatureCollection, and nested GeometryCollection objects are supported.

Existing bbox members are removed because they become invalid after reprojection.

When the target projection is equivalent to WGS84, the crs member is removed. Otherwise, the target CRS is stored as a named CRS. EPSG identifiers are written using the OGC URN form, for example EPSG:3857 becomes urn:ogc:def:crs:EPSG::3857.

Altitude values are preserved.

The input object is mutated and returned.

The operator checks that the input is GeoJSON-like and that both source and target projections are registered. It does not perform the full coordinate and topology validation provided by validateGeoJson; validate external or untrusted data before reprojection.

Parameters

Name	Type	Required	Description
geoJson	object	yes	Any valid GeoJSON object
target	string	yes	Name of a registered target projection

Returns

Type	Description
object	The reprojected GeoJSON object. The returned object is the same instance as geoJson

Throws

Throws if geoJson is not a valid GeoJSON object.

Throws if the source CRS is not a registered projection.

Throws if target is not a registered projection.

Examples

// WGS84 to Web Mercator
const point = {
  type: 'Point',
  coordinates: [2.35, 48.85]
}

reprojectGeoJson(point, 'EPSG:3857')

// {
//   type: 'Point',
//   coordinates: [261600.803..., 6249447.752...],
//   crs: {
//     type: 'name',
//     properties: {
//       name: 'urn:ogc:def:crs:EPSG::3857'
//     }
//   }
// }

// Source CRS is read from the GeoJSON object
const point = {
  type: 'Point',
  coordinates: [261600.8034, 6249447.7528],
  crs: {
    type: 'name',
    properties: {
      name: 'EPSG:3857'
    }
  }
}

reprojectGeoJson(point, 'EPSG:4326')

// {
//   type: 'Point',
//   coordinates: [2.35, 48.85]
// }

// Existing bbox is removed
const feature = {
  type: 'Feature',
  bbox: [2, 48, 3, 49],
  geometry: {
    type: 'Point',
    coordinates: [2.35, 48.85]
  },
  properties: {}
}

reprojectGeoJson(feature, 'EPSG:3857')

// feature.bbox === undefined

// Altitude is preserved
const point = {
  type: 'Point',
  coordinates: [2.35, 48.85, 100]
}

reprojectGeoJson(point, 'EPSG:3857')

// [261600.803..., 6249447.752..., 100]