使用Polygon在整个地图上绘制一个矩形

Question

I have been trying to draw a rectangle on the whole map(in a map activity) in Android Studio, i need a delimitation of the equator area, from one part of the map to the other. ( in a big rectangle) But every time i put the coordinates for the rectangle it goes the other way around, so it goes backwards and makes a small square from Pacific ocean to China , Australia and back.

Also, any idea how i can make a button take the shape of a country on the map?

package com.example.android.coffeeknowledge;

import android.content.res.Resources;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.util.Log;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MapStyleOptions;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.maps.model.Polygon;
import com.google.android.gms.maps.model.PolygonOptions;
import com.google.android.gms.maps.model.PolylineOptions;

public class coffeeMap extends FragmentActivity implements OnMapReadyCallback {

private GoogleMap mMap;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_coffee_map);
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
}

/**
 * Manipulates the map once available.
 * This callback is triggered when the map is ready to be used.
 * This is where we can add markers or lines, add listeners or move the camera. In this case,
 * we just add a marker near Sydney, Australia.
 * If Google Play services is not installed on the device, the user will be prompted to install
 * it inside the SupportMapFragment. This method will only be triggered once the user has
 * installed Google Play services and returned to the app.
 */
private static final LatLng cameraZoom = new LatLng(37.35, -122.0);
@Override
public void onMapReady(GoogleMap googleMap) {
    try{
        boolean success = googleMap.setMapStyle(
            MapStyleOptions.loadRawResourceStyle(this, R.raw.mapstyle));
            if(!success){
                Log.e("coffeeMap","Style parsing failed.");
            }

        }catch(Resources.NotFoundException e){
        Log.e("coffeeMap", "Can`t find style.Error: " , e);
    }

    mMap = googleMap;
   // Instantiates a new Polygon object and adds points to define a rectangle
    PolygonOptions rectOptions = new PolygonOptions()
            .fillColor(R.color.white)
            .add(new LatLng(24.376368, 101.181309),
                    new LatLng(-28.912738, 103.818027),
                    new LatLng(-26.841671, -117.944509),
                    new LatLng(27.616242, -122.020003),
                    new LatLng(24.376368, 101.181309));
            // Get back the mutable Polygon
    Polygon polygon = mMap.addPolygon(rectOptions);
    // Add a marker in Sydney and move the camera
    //mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(cameraZoom, 13));
    LatLng sydney = new LatLng(35.175321, -107.619365);
    mMap.addMarker(new MarkerOptions().position(sydney).title("Marker"));
 }
 }

Thank you.

Answer 1

The map api will always choose the shortest route between 2 points taking into account geodesic path or rectangular projection. The segments of interest in your example are:

new LatLng(-28.912738, 103.818027),   // A
new LatLng(-26.841671, -117.944509),  // B

and

new LatLng(27.616242, -122.020003),   // C
new LatLng(24.376368, 101.181309))    // D

These two segments will cross the anti-meridian (and not go the other way around) because that is the shortest path between those two points. (This is always what would be desired.)

So to overcome this in your example, simply add an intermediate mid-point (assuming non-geodesic, or rectangular projection) in the segments (AB and CD) to force it to go "the other way". Using AB as an example:

new LatLng(-28.912738, 103.818027),
new LatLng(-27.877204, -7.0),        // approximate midpoint in desired direction (M)
new LatLng(-26.841671, -117.944509),

So the original distance from AB (assuming geodesic) is 12830 km. And with the forced intermediate point is: AM 10320km and MB 10460km. These distance calculations are merely to demonstrate the point (pun intended).

The same approach applies to CD.

---

So in pictures, your OP view using:

PolygonOptions rectOptions = new PolygonOptions()
    .fillColor(R.color.colorPrimary)
            .add(new LatLng(24.376368, 101.181309),
                 new LatLng(-28.912738, 103.818027),
                 new LatLng(-26.841671, -117.944509),
                 new LatLng(27.616242, -122.020003),
                 new LatLng(24.376368, 101.181309));

is displayed as:

and with the 2 intermediate points:

    PolygonOptions rectOptions = new PolygonOptions()
            .fillColor(R.color.colorPrimary)
            .add(new LatLng(24.376368, 101.181309),
                    new LatLng(-28.912738, 103.818027),
                    new LatLng(-27.877204, -7.0),
                    new LatLng(-26.841671, -117.944509),
                    new LatLng(27.616242, -122.020003),
                    new LatLng( 25.9, -7.0),
                    new LatLng(24.376368, 101.181309));

is displayed as:

Just for fun, and to emphasize the midpoint determination depends on the projection, here is the same polygon using geodesic:

Finding the spherical midpoint for 2 points spanning an arc greater than pi radians is a problem for another day...

A handy online tool for more consideration: https://www.movable-type.co.uk/scripts/latlong.html .