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go.geojson

Go.geojson is a package for encoding and decoding GeoJSON into Go structs. Supports both the json.Marshaler and json.Unmarshaler interfaces as well as sql.Scanner for directly scanning PostGIS query results. The package also provides helper functions such as UnmarshalFeatureCollection, UnmarshalFeature and UnmarshalGeometry.

Important

This package is best for lightweight interaction with GeoJSON. If you want to actually do stuff with the geometry take a look at orb/geojson which decodes the geometries into orb types which you can do all sorts of things with.

To install

go get github.com/paulmach/go.geojson

To use, imports as package name `geojson`:

import "github.com/paulmach/go.geojson"

Examples

Unmarshalling (JSON -> Go)

go.geojson supports both the json.Marshaler and json.Unmarshaler interfaces as well as helper functions such as UnmarshalFeatureCollection, UnmarshalFeature and UnmarshalGeometry.

  // Feature Collection
  rawFeatureJSON := []byte(`
    { "type": "FeatureCollection",
      "features": [
        { "type": "Feature",
          "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
          "properties": {"prop0": "value0"}
        }
      ]
    }`)

  fc1, err := geojson.UnmarshalFeatureCollection(rawFeatureJSON)

  fc2 := geojson.NewFeatureCollection()
  err := json.Unmarshal(rawJSON, fc2)

  // Geometry
  rawGeometryJSON := []byte(`{"type": "Point", "coordinates": [102.0, 0.5]}`)
  g, err := geojson.UnmarshalGeometry(rawGeometryJSON)

  g.IsPoint() == true
  g.Point == []float64{102.0, 0.5}

Marshalling (Go -> JSON)

  g := geojson.NewPointGeometry([]float64{1, 2})
  rawJSON, err := g.MarshalJSON()

  fc := geojson.NewFeatureCollection()
  fc.AddFeature(geojson.NewPointFeature([]float64{1,2}))
  rawJSON, err := fc.MarshalJSON()

Scanning PostGIS query results

  row := db.QueryRow("SELECT ST_AsGeoJSON(the_geom) FROM postgis_table)

  var geometry *geojson.Geometry
  row.Scan(&geometry)

Dealing with different Geometry types

A geometry can be of several types, causing problems in a statically typed language. Thus there is a separate attribute on Geometry for each type. See the Geometry object for more details.

  g := geojson.UnmarshalGeometry([]byte(`
  	{
        "type": "LineString",
        "coordinates": [
          [102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
        ]
      }`))

  switch {
  case g.IsPoint():
  	// do something with g.Point
  case g.IsLineString():
  	// do something with g.LineString
  }

Feature Properties

GeoJSON Features can have properties of any type. This can cause issues in a statically typed language such as Go. So, included are some helper methods on the Feature object to ease the pain.

// functions to do the casting for you
func (f Feature) PropertyBool(key string) (bool, error) {
func (f Feature) PropertyInt(key string) (int, error) {
func (f Feature) PropertyFloat64(key string) (float64, error) {
func (f Feature) PropertyString(key string) (string, error) {

// functions that hide the error and let you define default
func (f Feature) PropertyMustBool(key string, def ...bool) bool {
func (f Feature) PropertyMustInt(key string, def ...int) int {
func (f Feature) PropertyMustFloat64(key string, def ...float64) float64 {
func (f Feature) PropertyMustString(key string, def ...string) string {

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