java - 如何在 Google map 上选择正确的缩放比例

Question

我构建了一个使用带有多个标记的 GMaps 的应用程序。用户可以添加或删除标记，但我的问题是选择合适的缩放级别来显示所有标记。

如果用户添加或删除标记，该缩放级别可以改变。

为了使相机居中，我使用以下代码:

double xMin = 90.0 ;
double xMax =  0.0 ;
double yMin = 90.0 ;
double yMax =  0.0 ;

LatLngBounds.Builder builder = new LatLngBounds.Builder();

for (Place place : places) {
                if (place.getLatitude() < xMin)
                    xMin = place.getLatitude();

                if (place.getLatitude() > xMax)
                    xMax = place.getLatitude();

                if (place.getLongitude() < yMin)
                    yMin = place.getLongitude();

                if (place.getLongitude() > yMax)
                    yMax = place.getLongitude();

                MarkerOptions markerOptions = new MarkerOptions();
                markerOptions.position(new LatLng(place.getLatitude(), place.getLongitude()));
                markerOptions.title(String.valueOf(place.getId()));
                Marker marker = this.googleMap.addMarker(markerOptions);
                allMarkersMap.put(marker, place);
                displayMarkersMap.put(marker, place);
                builder.include(marker.getPosition());
            }

            double xPos = (xMax + xMin) / 2;
            double yPos = (yMax + yMin) / 2;

            LatLngBounds bounds = builder.build();
            int padding = 1; // offset from edges of the map in pixels
            //CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngBounds(bounds, padding);
            //this.googleMap.moveCamera(cameraUpdate);
            LatLng latLng = new LatLng(xPos, yPos);
            CameraPosition cameraPosition = new CameraPosition.Builder().target(latLng).zoom(2).build();
            this.googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

但我没有找到具有良好缩放值的解决方案。

Answer 1

我知道您需要为 map 定义一个中心并确保所有标记都在 View 内。

在这种情况下，您可以计算包含您的标记的 LatLngBounds，然后使用 SphericalUtil.computeOffset、SphericalUtil.computeDistanceBetween 和来自 Google Maps API Utility Library 的 SphericalUtil.computeHeading 方法

private LatLngBounds findBounds(List<LatLng> positions, LatLng center) {
    // Add all the positions to a LatLngBounds (including center)
    LatLngBounds.Builder boundsBuilder = new LatLngBounds.Builder();
    for (LatLng position : positions) {
        boundsBuilder.include(position);
    }
    boundsBuilder.include(center);
    LatLngBounds bounds = boundsBuilder.build();

    // Compute the farthest location from the center among the bound corners
    LatLng northWest = new LatLng(bounds.northeast.latitude, bounds.southwest.longitude);
    LatLng southEast = new LatLng(bounds.southwest.latitude, bounds.northeast.longitude);
    LatLng farthest = findFarthestLocation(center, bounds.northeast, northWest, southEast, bounds.southwest);

    // Expand the bounds adding the projection of the farthest location from the center
    // in the oposite direction
    bounds = bounds.including(SphericalUtil.computeOffset(center,
            SphericalUtil.computeDistanceBetween(center, farthest),
            SphericalUtil.computeHeading(center, farthest) + 180));

    return bounds;
}

private LatLng findFarthestLocation(LatLng from, LatLng... locations) {
    LatLng farthest = null;

    for (LatLng location : locations) {
        if (farthest == null ||
                SphericalUtil.computeDistanceBetween(from, location) > SphericalUtil.computeDistanceBetween(from, farthest)) {
            farthest = location;
        }
    }

    return farthest;
}

你可以测试这个方法做

LatLng center = new LatLng(40.384213, -3.875244);
List<LatLng> positions = new ArrayList<>();
positions.add(new LatLng(43.153102, 2.914307));
positions.add(new LatLng(42.976521, 1.508057));
positions.add(new LatLng(42.492353, 0.123779));

Display display = getActivity().getWindowManager().getDefaultDisplay();
                Point size = new Point();
                display.getSize(size);
                int width  = size.x;
                int height = size.y;

LatLngBounds bounds = findBounds(positions,center);
mMap.animateCamera(CameraUpdateFactory.newLatLngBounds(bounds,width,height,10));