Google地图获得缩放级别的可见区域半径

Question

我正在构建一个应用，我在onCameraIdle中从API加载数据。该请求需要目标位置和半径，以便为我提供结果。

我用来从当前相机获取半径的代码是：

/**
 * @param map The Map on which to compute the radius.
 * @return The circle radius of the area visible on map, in meters.
 */
public float getRadiusVisibleOnMap(GoogleMap map) {
    VisibleRegion visibleRegion = map.getProjection().getVisibleRegion();

    LatLng farRight = visibleRegion.farRight;
    LatLng farLeft = visibleRegion.farLeft;
    LatLng nearRight = visibleRegion.nearRight;
    LatLng nearLeft = visibleRegion.nearLeft;

    float[] distanceWidth = new float[1];
    Location.distanceBetween(
            (farRight.latitude + nearRight.latitude) / 2,
            (farRight.longitude + nearRight.longitude) / 2,
            (farLeft.latitude + nearLeft.latitude) / 2,
            (farLeft.longitude + nearLeft.longitude) / 2,
            distanceWidth
    );


    float[] distanceHeight = new float[1];
    Location.distanceBetween(
            (farRight.latitude + nearRight.latitude) / 2,
            (farRight.longitude + nearRight.longitude) / 2,
            (farLeft.latitude + nearLeft.latitude) / 2,
            (farLeft.longitude + nearLeft.longitude) / 2,
            distanceHeight
    );

    float radius;

    if (distanceWidth[0] > distanceHeight[0]) {
        radius = distanceWidth[0];
    } else {
        radius = distanceHeight[0];
    }

    return radius;
}

我是从here

得到的

在某些情况下我只需要知道缩放级别，因此当缩放动画完成时，信息已经加载到地图上。

我尝试从here调整代码以获得知道缩放级别的半径，而不是相反。

public int getZoomLevel(Circle circle) {
    if (circle != null) {
        double radius = circle.getRadius();
        double scale = radius / 500;
        zoomLevel = (int) (16 - Math.log(scale) / Math.log(2));
    }
    return zoomLevel;
}

我得到了公式：

公式不正确。它没有输出正确的尺寸。对于14的缩放级别，我使用相机的VisibleRegion得到半径尺寸为2.697331km。如果我使用公式计算半径，结果是0.008km。

Answer 1

看起来最佳做法是找到适合内部地图矩形的最小半径值。

你几乎就在那里，使用下面的修改函数，使用Pythagorean theorem来找到包含地图“矩形”所需的最小半径。

@Override
public void onMapReady(GoogleMap googleMap) {
    this.googleMap = googleMap;
    googleMap.setOnMarkerClickListener(this);

    googleMap.setOnCameraIdleListener(() -> {
        CameraPosition cameraPosition = googleMap.getCameraPosition();
        double radiusInMeters = getMapVisibleRadius();
        double radiusInKilometers = radiusInMeters / 1000;
        double latitude = cameraPosition.target.latitude;
        double longitude = cameraPosition.target.longitude;

        // TODO you take it from here, 
        // I use firebase to get relevant markers based on the lat,long,radius

    });
}


private double getMapVisibleRadius() {
    VisibleRegion visibleRegion = googleMap.getProjection().getVisibleRegion();

    float[] distanceWidth = new float[1];
    float[] distanceHeight = new float[1];

    LatLng farRight = visibleRegion.farRight;
    LatLng farLeft = visibleRegion.farLeft;
    LatLng nearRight = visibleRegion.nearRight;
    LatLng nearLeft = visibleRegion.nearLeft;

    Location.distanceBetween(
            (farLeft.latitude + nearLeft.latitude) / 2,
            farLeft.longitude,
            (farRight.latitude + nearRight.latitude) / 2,
            farRight.longitude,
            distanceWidth
    );

    Location.distanceBetween(
            farRight.latitude,
            (farRight.longitude + farLeft.longitude) / 2,
            nearRight.latitude,
            (nearRight.longitude + nearLeft.longitude) / 2,
            distanceHeight
    );

    double radiusInMeters = Math.sqrt(Math.pow(distanceWidth[0], 2) + Math.pow(distanceHeight[0], 2)) / 2;
    return radiusInMeters;
}