Develop Reference

Generating BoundingBox for GeoJSON data - android

I'm drawing GeoJSON polygons on my map using the Android Map Utils that Google provides (compile 'com.google.maps.android:android-maps-utils:0.4'). However, the GeoJSON I get does not include a bounding box, so sometimes the map is way off. Here's an example of the polygon stuff I get back:
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And I'm just adding it to the map by doing:
geoJsonObject = new JSONObject(response);
GeoJsonLayer layer = new GeoJsonLayer(getMap(), geoJsonObject);
layer.addLayerToMap();
However, because there are no "bounds" supplied in the KVP data, so any time I try to do, layer.getBoundingBox(), I always get a return value of null. Is there a way to generate the bounding box myself once I know the coordinates?

Looking at the sources of GeoJsonLayer.java and GeoJsonParser.java it's obvious that there's no code to calculate the bounding box. Even the parseFeatureCollection() method just parses the bounding box if it's in the GeoJSON data.
However the bounding box is a LatLngBounds object and the class has a nested Builder class which can be used to build a LatLngBounds object:
// Get the bounding box builder.
LatLngBounds.Builder builder = LatLngBounds.builder();
// Get the coordinates
for (GeoJsonFeature feature : layer.getFeatures()) {
if (feature.hasGeometry()) {
GeoJsonGeometry geometry = feature.getGeometry();
List<? extends List<LatLng>> lists =
((GeoJsonPolygon) geometry).getCoordinates();
// Feed the coordinates to the builder.
for (List<LatLng> list : lists) {
for (LatLng latLng : list) {
builder.include(latLng);
}
}
}
}
// Assign the builder's return value to a bounding box.
LatLngBounds bb = builder.build();
So, if you have only GeoJsonPolygons to draw it's not that much hassle to get a bounding box.
For a more complete solution you would have to build a more elaborate mechanism to extract the coordinates from any GeoJSON geometry object type. They are all implementations of the GeoJsonGeometry interface. The first thing is to differentiate between GeoJsonGeometryCollection and all the rest:
private LatLngBounds getLatLngBoundingBox(GeoJsonLayer layer) {
List<LatLng> coordinates = new ArrayList<>();
for (GeoJsonFeature feature : layer.getFeatures()) {
if (feature.hasGeometry()) {
GeoJsonGeometry geometry = feature.getGeometry();
if (geometry.getType().equals("GeometryCollection")) {
List<GeoJsonGeometry> geometries =
((GeoJsonGeometryCollection)geometry).getGeometries();
for (GeoJsonGeometry geom : geometries) {
coordinates.addAll(getCoordinatesFromGeometry(geom));
}
}
else {
coordinates.addAll(getCoordinatesFromGeometry(geometry));
}
}
}
// Get the bounding box builder.
LatLngBounds.Builder builder = LatLngBounds.builder();
// Feed the coordinates to the builder.
for (LatLng latLng : coordinates) {
builder.include(latLng);
}
LatLngBounds boundingBoxFromBuilder = builder.build();
//return boundingBox;
return boundingBoxFromBuilder;
}
The actual code (may have bugs) for extracting the coordinates would be something like:
private List<LatLng> getCoordinatesFromGeometry(GeoJsonGeometry geometry) {
List<LatLng> coordinates = new ArrayList<>();
// GeoJSON geometry types:
// http://geojson.org/geojson-spec.html#geometry-objects
switch (geometry.getType()) {
case "Point":
coordinates.add(((GeoJsonPoint) geometry).getCoordinates());
break;
case "MultiPoint":
List<GeoJsonPoint> points = ((GeoJsonMultiPoint) geometry).getPoints();
for (GeoJsonPoint point : points) {
coordinates.add(point.getCoordinates());
}
break;
case "LineString":
coordinates.addAll(((GeoJsonLineString) geometry).getCoordinates());
break;
case "MultiLineString":
List<GeoJsonLineString> lines =
((GeoJsonMultiLineString) geometry).getLineStrings();
for (GeoJsonLineString line : lines) {
coordinates.addAll(line.getCoordinates());
}
break;
case "Polygon":
List<? extends List<LatLng>> lists =
((GeoJsonPolygon) geometry).getCoordinates();
for (List<LatLng> list : lists) {
coordinates.addAll(list);
}
break;
case "MultiPolygon":
List<GeoJsonPolygon> polygons =
((GeoJsonMultiPolygon) geometry).getPolygons();
for (GeoJsonPolygon polygon : polygons) {
for (List<LatLng> list : polygon.getCoordinates()) {
coordinates.addAll(list);
}
}
break;
}
return coordinates;
}
You would then use the code like:
LatLngBounds bb = getLatLngBoundingBox(layer);

Related

I'm in a project with Xamarin Forms and OpenStreetMap.
I'm trying get the coordinates in the center of map.
This my code that create the map
public static Map CreateMap(double latitud, double longitud)
{
map = new Map();
var location = new Point(longitud, latitud);
var sphericalMercatorCoordinate = SphericalMercator.FromLonLat(location.X, location.Y);
map.Layers.Add(OpenStreetMap.CreateTileLayer());
map.Home = n => n.NavigateTo(sphericalMercatorCoordinate, map.Resolutions[15]);
return map;
}
This is my code in file xaml.
<maps:MapView x:Name="MapView"
TouchMove="MapView_TouchMove"
MyLocationFollow="True"
IsMyLocationButtonVisible="False"
VerticalOptions="FillAndExpand"
HorizontalOptions="FillAndExpand" />
Try adding a method "TouchMove". But only get Bounds of map and not the coordinate.
private void MapView_TouchMove(object sender, Mapsui.UI.TouchedEventArgs e)
{
var center = MapView.Bounds.Center;
}
So, try add a Method MapClicked, for invoke this method from "MapView_TouchMove" but i dont know how invoke.
private void MapView_MapClicked(object sender, MapClickedEventArgs e)
{
var lat = e.Point.Latitude;
}
Any idea..???
Thanks.

looking at the API docs, Envelope appears to return what you want
Gets the extents of the map based on the extents of all the layers in
the layers collection
The MapView control has a Map property, from which you can get Envelope

I want to use the world map in Unity and have been looking at the API of various map services. I need to show a screenshot (a static map with markers) on the screen, and move to the full map view to navigate it after clicking on it.
MapBox managed to display the map with the selected coordinates and add test markers, but that's all I can do with a query like this: https://api.mapbox.com/styles/v1/mapbox/streets-v11/static/url-https%3A%2F%2Fwww.mapbox.com%2Fimg%2Frocket.png(-76.9,38.9)/-76.9,38.9,15/1000x1000?access_token=pk.eyJ1IjoiZGVuZGVhZCIsImEiOiJja2F1dha4egixnnfhmnvtc2u0y3bua2ntin0.GGOyhgN_fEqtPpPc5n6OLg because this request returns a jpg image.
They also have a plugin for Unity, but it's only used in 3d projects and does not allow me to configure the display in 2d.
In MapBox, the mapping I need is implemented using JavaScript for Web and Java for Android. On Android I can do what I need. I can connect to the API on Android, but will I be able to use it in Unity later?
It's the same with Google maps.
Actually, the question is, did someone work with map services in Unity? And how can this be implemented correctly?

I don't know if this is still relevant, but I used Mapbox in Unity (the Mapbox plugin) to create a AR Soundscape by "registering" GameObjects to coordinates and moving them in real-time when the map is moved.
Your problem sounds an awful lot like the one I solved with that.
Basically you provide the Lat/Lon values for your objects and convert them to Unity world space coordinates using the AbstractMap.GeoToWorldPosition() function.
I used a raycast to actually pull that off in-engine, which is quite convenient.
//Edit:
Unity is quite capable of handling 2D projects. You just have to configure it properly and build your project around it.
The following is the class that I use to handle all positioning-related calculations. Maybe it's of some help to you.
namespace TehMightyPotato.Positioning
{
[Serializable]
public class GeoPosition
{
[Tooltip(
"Update frequency of position polling. Update every n-th frame. 1 is every frame, 60 is every 60th frame.")]
[Range(1, 60)]
public int positionUpdateFrequency = 1;
[Tooltip("Should the object have a specified altitude?")]
public bool useYOffset = false;
[Tooltip("If useMeterConversion is activated the yOffsets unit is meters, otherwise its unity units.")]
public bool useMeterConversion = false;
[Tooltip("The actual y position of the object in m or unity units depending on useMeterConversion.")]
public float yOffset = 0;
[Tooltip("X is LAT, Y is LON")]public Vector2d geoVector;
[HideInInspector] public float worldRelativeScale;
// Apply the result of this function to your gameobjects transform.position on every frame to keep them on this position.
public Vector3 GetUnityWorldSpaceCoordinates(AbstractMap map)
{
UpdateWorldRelativeScale(map);
var worldSpaceCoordinates = map.GeoToWorldPosition(geoVector, false);
if (useYOffset)
{
worldSpaceCoordinates.y = yOffset;
}
return worldSpaceCoordinates;
}
public void UpdateWorldRelativeScale(AbstractMap map)
{
worldRelativeScale = map.WorldRelativeScale;
}
public void SetGeoVectorFromRaycast(Vector3 position, AbstractMap map, LayerMask layerMask)
{
var ray = new Ray(position, Vector3.down);
if (Physics.Raycast(ray, out var hitInfo, Mathf.Infinity, layerMask))
{
geoVector = map.WorldToGeoPosition(hitInfo.point);
}
else
{
throw new NullReferenceException("Raycast did not hit the map. Did you turn on map preview?");
}
}
public void SetYOffsetFromRaycast(AbstractMap map, Vector3 position, LayerMask layerMask)
{
UpdateWorldRelativeScale(map);
// using raycast because of possible y-non-zero maps/ terrain etc.
var ray = new Ray(position, Vector3.down);
if (Physics.Raycast(ray, out var hitInfo, Mathf.Infinity, layerMask))
{
var worldSpaceDistance = Vector3.Distance(position, hitInfo.point);
if (useMeterConversion)
{
yOffset = worldSpaceDistance * worldRelativeScale;
}
else
{
yOffset = worldSpaceDistance;
}
}
else
{
throw new NullReferenceException("Could not find map below. Is map preview turned on?");
}
}
}
}

I'm fetching marker icon URL from server using volley library.
String icon_url = catObj.getString("icon_url");
and then assigning the icon_url to the variable declared in MyMarker class
this.mIconUrl = icon_url;
Now in setUpMap method I'm stuck how to replace marker icon with image I'm fetching from server. Here is the code for this:
for(MyMarker myMarker : markers)
{
Marker marker = mMap.addMarker(new MarkerOptions()
.position(myMarker.getmLatLng())
.title(myMarker.getmLabel())
.snippet(myMarker.getmIcon())
.icon( ??? )); //myMarker.getmIconUrl won't work as it return String
}
I've also tried from this link but it shows the image in ImageView:
http://www.simplifiedcoding.net/android-volley-example-to-load-image-from-internet/
Any help is appreciated.

I use BitmapFactory to render custom pattern. You can use similar to load bitmap from URL :
Android google mapv2 icon from URL
Or this just replace HttpUrlConnection with Volley :
google map api v2 add icon from url android
And when you get bitmap you can use .icon(BitmapDescriptorFactory.fromBitmap(bmp)));

For getting Images using Volley you have to first create an instance of MarkerOptions and then use Volley ImageLoader to get images from server and then set image to marker after you get it's bitmap. you may possibly have something like this:
ImageLoader imageloader =VolleySingleton.getInstance(getApplicationContext()).getImageLoader();
for(MyMarker myMarker : markers)
{
final MarkerOptions markerOptions = new MarkerOptions()
.position(myMarker.getmLatLng());
imageloader.get(myMarker.getmIconUrl(), new ImageLoader.ImageListener() {
#Override
public void onResponse(ImageLoader.ImageContainer response, boolean isImmediate)
{
Bitmap bitmap = response.getBitmap();
if (bitmap != null) {
markerOptions.icon(BitmapDescriptorFactory.fromBitmap(bitmap));
//add marker to your map using below codes
// mapMarkers is a HashMap of your markers and your possible values for that location(eg. id,name,..)
Marker marker = mMap.addMarker(markerOptions);
mapMarkers.put(marker, myMarker.getLocationId());
}
}
#Override
public void onErrorResponse(VolleyError error) {
}
});
}

I'm trying out the Google API V2 Heatmap (Android) which was introduced this february and it's not working entirely. I'm not sure if it's the same problem as Google Maps API v2 HeatMap Won't Reliably Display (and I can't contact him by comments because I don't have enough rep.. :c ).
Using locations from file
Anyway, what I was trying to do was an App with just a GoogleMap and the same locations as in their guide (https://developers.google.com/maps/documentation/android/utility/heatmap) and when I launch it, I can only see 3/5 locations.
I tried adding more points and still, it's consistently not showing them all, but I can't see a pattern or something. The code is the same as in their guide.
private void addHeatMap() {
List<LatLng> list = null;
// Get the data: latitude/longitude positions of police stations.
try {
list = readItems(R.raw.police_stations);
} catch (JSONException e) {
Toast.makeText(this, "Problem reading list of locations.", Toast.LENGTH_LONG).show();
}
// Create a heat map tile provider, passing it the latlngs of the police stations.
mProvider = new HeatmapTileProvider.Builder()
.data(list)
.build();
// Add a tile overlay to the map, using the heat map tile provider.
mOverlay = mMap.addTileOverlay(new TileOverlayOptions().tileProvider(mProvider));
}
private ArrayList<LatLng> readItems(int resource) throws JSONException {
ArrayList<LatLng> list = new ArrayList<LatLng>();
InputStream inputStream = getResources().openRawResource(resource);
String json = new Scanner(inputStream).useDelimiter("\\A").next();
JSONArray array = new JSONArray(json);
for (int i = 0; i < array.length(); i++) {
JSONObject object = array.getJSONObject(i);
double lat = object.getDouble("lat");
double lng = object.getDouble("lng");
LatLng latLng = new LatLng(lat, lng);
list.add(latLng);
}
return list;
}
Trying with weighted locations had the same result, some of them showing and some not.
Using locations "onClick"
In this case, normal LatLng were added and the map was updated until I got to the equator and then it stopped :p.
For the case of weightedLatLngs, it didn't update/show any :(
That's basically it... I don't know where to look for more information, whether it's something with the API, the device or something else.
Does anyone know why this might happen and/or where to look for a solution ?
Thank you in advance !
Btw, I'm using Android 4.0.4 on a Samsung Galaxy S Duos if that may prove useful..

The Googlemaps API for Heatmap only allows for 1,000 plotted points. You can reduced that by filtering out your original data or by converting to "weighted locations".

This looks like it was caused by this bug, where bounds calculations were excluding max values.
This is now fixed.

I am doing android app for field drawing and now I am making share function. Is there are any way to pass field coordinates from mobile to maps.google.com, make link, and send this link for example to friend via sms or email, that he just need to push the link and my drawed field will show up to him in browser? Is there any tool to do this or I need to create some web app for this?

Try out it
// To draw boundray on map
private void drawPolygon() {
polygonOptions = new PolygonOptions(); // consider new options
setStrokeWidth();
for (LatLng latLng : drawCoordinates) {
Marker marker = googleMap.addMarker(new MarkerOptions().position(latLng).title(latLng.toString()));
marker.setVisible(false);
polygonOptions.add(marker.getPosition()).strokeColor(Color.RED);
polygonOptions.fillColor(Color.TRANSPARENT);
polygonOptions.visible(true);
}
List<LatLng> points = polygonOptions.getPoints();
if (!points.isEmpty()) {
polygon = googleMap.addPolygon(polygonOptions);
Log.i("Poly lines","Successfully added polyline on map");
}
}