Android Google Map how to check if user is in marker rectangle region

Question

I am using Google Maps, and want to be able to detect if a user is in the rectangle of a Marker (placed on a map), using the user's current location. I have the user's current location coordinates (latitude and longitude) and the marker's coordinates but do not know how to calculate whether the user is in the area.

Answer 1

The short answer is to use the PolyUtil.containsLocation using the rectangle corner points (centered on the marker) and the user's location:

boolean isWithin = PolyUtil.containsLocation(userPt, rectanglePts, true);

Here is docs on map utils. And the PolyUtil java docs

Here is a code fragment demonstrating. Note the rectangle rotation is handled by the utility so it need not be aligned to the coordinate system. In fact it doesn't even need to be a rectangle.

(I chose to use circles for display purposes but can be replaced with markers.):

In this example, the marker is drawn as a circle in green, the containing rectangle and two arbitrary points (possible user locations) to show result of calculation (RED=in, BLUE=out).

// Create rectangle coordinates 
LatLng upperLeft = new LatLng(39.274659,-77.639552);
LatLng upperRight = SphericalUtil.computeOffset(upperLeft, 12000, 120);
LatLng lowerRight = SphericalUtil.computeOffset(upperRight, 5000, 210);
LatLng lowerLeft = SphericalUtil.computeOffset(lowerRight, 12000, 300);

// Make a list for the polygon
List<LatLng> polygonPts = new ArrayList<>();
    polygonPts.add(upperLeft);
    polygonPts.add(upperRight);
    polygonPts.add(lowerRight);
    polygonPts.add(lowerLeft);

// Draw rectangle
mMap.addPolygon(new PolygonOptions().addAll(polygonPts).geodesic(true).strokeColor(Color.BLACK));

// Draw marker (center of rectangle)
LatLng mPos = SphericalUtil.computeOffset(SphericalUtil.computeOffset(upperLeft,6000,120),2500, 210);

// Now add a circle to represent the marker - circles display nicer
mMap.addCircle(new CircleOptions().center(mPos).fillColor(Color.GREEN).radius(300).strokeWidth(1));


// Add two points and compute whether they are inside or outside rectangle and
// set color based on that (RED=inside BLUE=outside)
LatLng circleInside = SphericalUtil.computeOffset(mPos,1000, 320);
LatLng circleOutside = SphericalUtil.computeOffset(mPos,4000, 45);

// Determine if point is inside rectangle and set color accordingly.
int insideCircleColor = (PolyUtil.containsLocation(circleInside, polygonPts, true) ? Color.RED : Color.BLUE);
int outsideCircleColor = (PolyUtil.containsLocation(circleOutside, polygonPts, true) ? Color.RED : Color.BLUE);

// Add to map
mMap.addCircle(new CircleOptions().center(SphericalUtil.computeOffset(circleInside,1000, 320)).fillColor(insideCircleColor).radius(200).strokeWidth(1));
mMap.addCircle(new CircleOptions().center(SphericalUtil.computeOffset(circleOutside,1000, 320)).fillColor(outsideCircleColor).radius(200).strokeWidth(1));

// and zoom to center
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(mPos, 12.0f));

And display: