GeoJSON
The Mapbox Java SDK's GeoJSON module provides support for GeoJSON, an open standard file format for representing map data. Read the GeoJSON specification and the Mapbox Glossary's GeoJSON entry for more information about GeoJSON.
Geometries
The Java SDK provides classes for all GeoJSON geometry types. Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon, and GeometryCollection all end up implementing the Geometry interface. This shared interface gives you flexibility as you work with the Java SDK and potentially other Mapbox SDKs for Android.
The Point object represents a single geographical coordinate. It contains two values, longitude and latitude, in that order. This order is the reverse of the LatLng object in the Mapbox Maps SDK for Android. If you're using the Maps SDK and the Java SDK together, you'll need to convert between Point and LatLng objects.
val point = Point.fromLngLat(LONGITUDE, LATITUDE) // Java SDK
val latLng = LatLng(point.latitude(), point.longitude()) // Maps SDK
val point = Point.fromLngLat(latLng.longitude, latLng.latitude)
All geometry classes can be created via several different static methods. Always use a static method to create a GeoJSON geometry class.
Creating a single Polygon:
val polygon: Polygon = Polygon.fromLngLats(listOfPointList)
val polygonFromOuterInner: Polygon = Polygon.fromOuterInner(outerLineStringObject,innerLineStringObject)
Creating a single MultiLineString:
val multiLineString = MultiLineString.fromLineString(singleLineString)
val multiLineStringFromLngLat = MultiLineString.fromLngLats(listOfPointList)
val multiLineStringFromJson = MultiLineString.fromJson(JSON_STRING)
Feature and FeatureCollection
In the GeoJSON specification, a feature is an individual (or in some cases, a group of) points, lines, or polygons. Read more about features in the Mapbox Glossary. A group of features is called a feature collection.
The Java SDK's GeoJSON module also provides Feature and FeatureCollection classes. These classes can be combined with the various GeoJSON geometry classes.
val pointFeature = Feature.fromGeometry(Point.fromLngLat(LONGITUDE, LATITUDE))
val multiPointFeature = Feature.fromGeometry(MultiPoint.fromLngLats(listOfPoints))
val featureCollectionFromSingleFeature = FeatureCollection.fromFeature(pointFeature)
val featureCollection: FeatureCollection = FeatureCollection.fromFeatures(listOfFeatures)
val featureCollectionFromJson = FeatureCollection.fromJson(jsonString)
Cast to a specific geometry object
A Feature's Geometry can be cast to a specific geometry object.
In the code below, a Feature is used to create a Polygon:
val polygonFeatureJson =
"""
{
"type": "Feature",
"properties": {},
"geometry": {
"type": "Polygon",
"coordinates": [
[
[
-34.453125,
-45.08903556483102
],
[
71.71875,
-45.08903556483102
],
[
71.71875,
43.32517767999296
],
[
-34.453125,
43.32517767999296
],
[
-34.453125,
-45.08903556483102
]
]
]
}
}
"""
val singleFeature = Feature.fromJson(polygonFeatureJson)
val polygon = singleFeature.geometry() as Polygon?
Check a geometry type
You can check a Feature's geometry type. In the code below, a log message would appear whenever a Feature is a Point:
val featureCollection = FeatureCollection.fromFeatures(featureList)
featureCollection.features()?.let { featureList ->
for (singleFeature in featureList) {
if (singleFeature.geometry() is Point) {
Log.d(TAG, "is a Point geometry")
}
}
}
Use with the Maps SDK
When installed with Maven, the Mapbox Maps SDK for Android includes the Java SDK's GeoJSON module, which means you don't have to explicitly declare the Java SDK module if you're already using the Maps SDK. If you install the Maps SDK via direct download, you will need to declare the Java SDK explicitly.
Because of the Maps SDK's dependency on the GeoJSON module, the Maps SDK has been developed to support the Geometry, Feature, and FeatureCollection classes.
GeoJSON updates
The Java and Maps SDKs are often used together to create a Maps SDK GeoJsonSource with a Feature or FeatureCollection.
For example, here's how you can create a GeoJsonSource with a Feature and then add the GeoJsonSource to the map.
mapboxMap.getStyle {
// Create a list to store our line coordinates.
val routeCoordinates = ArrayList<Point>()
routeCoordinates.add(Point.fromLngLat(-118.394391, 33.397676))
routeCoordinates.add(Point.fromLngLat(-118.370917, 33.391142))
// Create the LineString from the list of coordinates and then make a GeoJSON FeatureCollection so that you can add the line to our map as a layer.
val lineString = LineString.fromLngLats(routeCoordinates)
val feature = Feature.fromGeometry(lineString)
val geoJsonSource = GeoJsonSource("geojson-source", feature)
it.addSource(geoJsonSource)
}
}
You can also update a GeoJsonSource's GeoJSON data to visually update the data on the map. Rather than passing through a Feature or FeatureCollection in the source.setGeoJson() method, you can pass a Geometry object to setGeoJson() directly.
For example, here's how to set a GeoJsonSource's GeoJSON data with a LineString:
mapboxMap?.getStyle { style ->
val source = style.getSourceAs<GeoJsonSource>(sourceId)
if (source != null && directionsRoute.geometry() != null) {
source.setGeoJson(LineString.fromPolyline(directionsRoute.geometry()!!, Constants.PRECISION_6))
}
}
Serialize and deserialize geometries
There might be a situation where you want to pass geometry data from one part of your project to another. A common case is putting data into an Android Intent as you start a new activity.
The geometry classes all have fromJson() and toJson() static methods, which help with serialization. The formatted valid JSON String passed through the fromJson() method will create the geometry object. This fromJson() method also means you can use Gson or other serialization/deserialization strategies.
val multiLineStringFromJson = MultiPolygon.fromJson(JSON_STRING)
val multiPolygonString = multiPolygon.toJson()