百度地图判断坐标是否在屏幕显示范围

开发时对接的百度地图，需要统计有多少个坐标点在屏幕的显示范围之内，百度地图的BMKPolygonContainsCoordinate函数可以判断点是否在多边形内,如下：

/**
 *判断点是否在多边形内
 *@param point 待判断的经纬度点
 *@param polygon 目标多边形的顶点数组
 *@param count 目标多边形顶点数组元素个数
 *@return 如果在内，返回YES，否则返回NO
 */
UIKIT_EXTERN BOOL BMKPolygonContainsCoordinate(CLLocationCoordinate2D point, CLLocationCoordinate2D *polygon, NSUInteger count);

判断一个坐标是否在屏幕的显示范围，代码如下：

- (BOOL)isItOnTheScreenAndBMKMapView:(BMKMapView *)mapView AndCLLocationCoordinate2D:(CLLocationCoordinate2D)coor{
    // 当前屏幕中心点的经纬度
    double centerLongitude = mapView.region.center.longitude;
    double centerLatitude = mapView.region.center.latitude;
    //当前屏幕显示范围的经纬度
    CLLocationDegrees pointssLongitudeDelta = mapView.region.span.longitudeDelta;
    CLLocationDegrees pointssLatitudeDelta = mapView.region.span.latitudeDelta;
    double leftUpLong = centerLongitude + pointssLongitudeDelta/2.0;
    double leftUpLati = centerLatitude - pointssLatitudeDelta/2.0;
    double leftDownLong = centerLongitude - pointssLongitudeDelta/2.0;
    double leftDownlati = centerLatitude - pointssLatitudeDelta/2.0;
    double rightDownLong = centerLongitude - pointssLongitudeDelta/2.0;
    double rightDownLati = centerLatitude + pointssLatitudeDelta/2.0;
    double rightUpLong = centerLongitude + pointssLongitudeDelta/2.0;
    double rightUpLati = centerLatitude + pointssLatitudeDelta/2.0;
    //构造BMKPolygonContainsCoordinate函数的参数数组
    CLLocationCoordinate2D coordinates[4];
    coordinates[0].latitude = leftUpLati;
    coordinates[0].longitude = leftUpLong;
    coordinates[1].latitude = leftDownlati;
    coordinates[1].longitude = leftDownLong;
    coordinates[2].latitude =  rightDownLati;
    coordinates[2].longitude = rightDownLong;
    coordinates[3].latitude = rightUpLati;
    coordinates[3].longitude = rightUpLong;
    
    return BMKPolygonContainsCoordinate(coor,coordinates,4);
    
}

需要注意的是在构造参数数组时，依次传入的顶点经纬度坐标顺序不能混乱，可以借助百度地图的- (BMKOverlayView *)mapView:(BMKMapView *)mapView viewForOverlay:(id <BMKOverlay>)overlay;函数进行区域验证，如下：

/**
 *根据overlay生成对应的View
 *@param mapView 地图View
 *@param overlay 指定的overlay
 *@return 生成的覆盖物View
 */
- (BMKOverlayView *)mapView:(BMKMapView *)mapView viewForOverlay:(id <BMKOverlay>)overlay;

- (BOOL)isItOnTheScreenAndBMKMapView:(BMKMapView *)mapView AndCLLocationCoordinate2D:(CLLocationCoordinate2D)coor{
    // 当前屏幕中心点的经纬度
    double centerLongitude = mapView.region.center.longitude;
    double centerLatitude = mapView.region.center.latitude;
    //当前屏幕显示范围的经纬度
    CLLocationDegrees pointssLongitudeDelta = mapView.region.span.longitudeDelta;
    CLLocationDegrees pointssLatitudeDelta = mapView.region.span.latitudeDelta;
    double leftUpLong = centerLongitude + pointssLongitudeDelta/2.0;
    double leftUpLati = centerLatitude - pointssLatitudeDelta/2.0;
    double leftDownLong = centerLongitude - pointssLongitudeDelta/2.0;
    double leftDownlati = centerLatitude - pointssLatitudeDelta/2.0;
    double rightDownLong = centerLongitude - pointssLongitudeDelta/2.0;
    double rightDownLati = centerLatitude + pointssLatitudeDelta/2.0;
    double rightUpLong = centerLongitude + pointssLongitudeDelta/2.0;
    double rightUpLati = centerLatitude + pointssLatitudeDelta/2.0;
    //构造BMKPolygonContainsCoordinate函数的参数数组
    CLLocationCoordinate2D coordinates[4];
    coordinates[0].latitude = leftUpLati;
    coordinates[0].longitude = leftUpLong;
    coordinates[1].latitude = leftDownlati;
    coordinates[1].longitude = leftDownLong;
    coordinates[2].latitude =  rightDownLati;
    coordinates[2].longitude = rightDownLong;
    coordinates[3].latitude = rightUpLati;
    coordinates[3].longitude = rightUpLong;
    
    BMKPolygon  *polygon = [BMKPolygon polygonWithCoordinates:coordinates count:4];
    [_mapView addOverlay:polygon];
    
    return BMKPolygonContainsCoordinate(coor,coordinates,4);
    
}

- (BMKOverlayView *)mapView:(BMKMapView *)mapView viewForOverlay:(id <BMKOverlay>)overlay{
    if ([overlay isKindOfClass:[BMKPolygon class]]){
        BMKPolygonView* polygonView = [[BMKPolygonView alloc] initWithOverlay:overlay];
        polygonView.strokeColor = [[UIColor alloc] initWithRed:0.0 green:0 blue:0.5 alpha:1];
        polygonView.fillColor = [[UIColor alloc] initWithRed:0 green:1 blue:1 alpha:0.2];
        polygonView.lineWidth = 2.0;
        polygonView.lineDash = YES;
        return polygonView;
    }
    return nil;
}

正常顺序下，区域是这样的： 屏幕快照 2019-07-30 下午6.44.23.png

而打乱顺序后，得到的区域可能是这样的：

屏幕快照 2019-07-30 下午6.49.04.png