109 lines
4.1 KiB
Markdown
109 lines
4.1 KiB
Markdown
go.geojson
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==========
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Go.geojson is a package for **encoding and decoding** [GeoJSON](http://geojson.org/) into Go structs.
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Supports both the [json.Marshaler](http://golang.org/pkg/encoding/json/#Marshaler) and [json.Unmarshaler](http://golang.org/pkg/encoding/json/#Unmarshaler)
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interfaces as well as [sql.Scanner](http://golang.org/pkg/database/sql/#Scanner) for directly scanning PostGIS query results.
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The package also provides helper functions such as `UnmarshalFeatureCollection`, `UnmarshalFeature` and `UnmarshalGeometry`.
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### Important
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This package is best for lightweight interaction with GeoJSON. If you want to actually do
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stuff with the geometry take a look at [orb/geojson](https://github.com/paulmach/orb/tree/master/geojson) which
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decodes the geometries into [orb](https://github.com/paulmach/orb) types which you can do all sorts of things with.
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#### To install
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go get github.com/paulmach/go.geojson
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#### To use, imports as package name `geojson`:
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import "github.com/paulmach/go.geojson"
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[](https://travis-ci.org/paulmach/go.geojson)
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[](https://godoc.org/github.com/paulmach/go.geojson)
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## Examples
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* #### Unmarshalling (JSON -> Go)
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go.geojson supports both the [json.Marshaler](http://golang.org/pkg/encoding/json/#Marshaler) and [json.Unmarshaler](http://golang.org/pkg/encoding/json/#Unmarshaler) interfaces as well as helper functions such as `UnmarshalFeatureCollection`, `UnmarshalFeature` and `UnmarshalGeometry`.
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// Feature Collection
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rawFeatureJSON := []byte(`
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{ "type": "FeatureCollection",
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"features": [
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{ "type": "Feature",
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"geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
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"properties": {"prop0": "value0"}
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}
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]
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}`)
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fc1, err := geojson.UnmarshalFeatureCollection(rawFeatureJSON)
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fc2 := geojson.NewFeatureCollection()
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err := json.Unmarshal(rawJSON, fc2)
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// Geometry
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rawGeometryJSON := []byte(`{"type": "Point", "coordinates": [102.0, 0.5]}`)
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g, err := geojson.UnmarshalGeometry(rawGeometryJSON)
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g.IsPoint() == true
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g.Point == []float64{102.0, 0.5}
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* #### Marshalling (Go -> JSON)
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g := geojson.NewPointGeometry([]float64{1, 2})
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rawJSON, err := g.MarshalJSON()
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fc := geojson.NewFeatureCollection()
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fc.AddFeature(geojson.NewPointFeature([]float64{1,2}))
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rawJSON, err := fc.MarshalJSON()
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* #### Scanning PostGIS query results
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row := db.QueryRow("SELECT ST_AsGeoJSON(the_geom) FROM postgis_table)
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var geometry *geojson.Geometry
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row.Scan(&geometry)
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* #### Dealing with different Geometry types
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A geometry can be of several types, causing problems in a statically typed language.
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Thus there is a separate attribute on Geometry for each type.
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See the [Geometry object](https://godoc.org/github.com/paulmach/go.geojson#Geometry) for more details.
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g := geojson.UnmarshalGeometry([]byte(`
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{
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"type": "LineString",
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"coordinates": [
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[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
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]
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}`))
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switch {
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case g.IsPoint():
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// do something with g.Point
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case g.IsLineString():
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// do something with g.LineString
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}
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## Feature Properties
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GeoJSON [Features](http://geojson.org/geojson-spec.html#feature-objects) can have properties of any type.
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This can cause issues in a statically typed language such as Go.
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So, included are some helper methods on the Feature object to ease the pain.
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// functions to do the casting for you
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func (f Feature) PropertyBool(key string) (bool, error) {
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func (f Feature) PropertyInt(key string) (int, error) {
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func (f Feature) PropertyFloat64(key string) (float64, error) {
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func (f Feature) PropertyString(key string) (string, error) {
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// functions that hide the error and let you define default
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func (f Feature) PropertyMustBool(key string, def ...bool) bool {
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func (f Feature) PropertyMustInt(key string, def ...int) int {
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func (f Feature) PropertyMustFloat64(key string, def ...float64) float64 {
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func (f Feature) PropertyMustString(key string, def ...string) string {
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