android google maps Polygon add circle hole

Question

hi currently im working on a google maps app.

and i want the following effect:

To do this i was thing of first creating a polygon overlay over the c

Answer 1

Unfortunately, Google Maps library doesn't let to get an array of LatLng of the circle. So you need to draw a circle yourself.

Basically, you need to provide a method that will create a hole (circle) for a polygon which fills your map.

There are 3 steps.

1 step is to build a method that will create a polygon that covers an entire map.

private static List createOuterBounds() {
    float delta = 0.01f;

    return new ArrayList() {{
        add(new LatLng(90 - delta, -180 + delta));
        add(new LatLng(0, -180 + delta));
        add(new LatLng(-90 + delta, -180 + delta));
        add(new LatLng(-90 + delta, 0));
        add(new LatLng(-90 + delta, 180 - delta));
        add(new LatLng(0, 180 - delta));
        add(new LatLng(90 - delta, 180 - delta));
        add(new LatLng(90 - delta, 0));
        add(new LatLng(90 - delta, -180 + delta));
    }};
}

2 step is to create a method that will return an Iterable with LatLngs of the circle.

private static Iterable createHole(LatLng center, int radius) {
    int points = 50; // number of corners of inscribed polygon

    double radiusLatitude = Math.toDegrees(radius / (float) EARTH_RADIUS);
    double radiusLongitude = radiusLatitude / Math.cos(Math.toRadians(center.latitude));

    List result = new ArrayList<>(points);

    double anglePerCircleRegion = 2 * Math.PI / points;

    for (int i = 0; i < points; i++) {
        double theta = i * anglePerCircleRegion;
        double latitude = center.latitude + (radiusLatitude * Math.sin(theta));
        double longitude = center.longitude + (radiusLongitude * Math.cos(theta));

        result.add(new LatLng(latitude, longitude));
    }

    return result;
}

3 and the last step is to use these methods for PolygonOptions creation.

static PolygonOptions createPolygonWithCircle(Context context, LatLng center, int radius) {
    return new PolygonOptions()
        .fillColor(ContextCompat.getColor(context, R.color.grey_500_transparent))
        .addAll(createOuterBounds())
        .addHole(createHole(center, radius))
        .strokeWidth(0);
}

I have also created a demo repository which contains an app which draws a needed circle. https://github.com/AntonyGolovin/Google-Map-mask. All needed logic is contained in MapHelper.java class.

Result: