//清理坐标数据的视图和数据
    [_bMapView removeAnnotations:_mapAnnotations];
    [_mapAnnotations removeAllObjects];
    [_carPointArray removeAllObjects];
    //声明解析时对坐标数据的位置区域的筛选，包括经度和纬度的最小值和最大值
    CLLocationDegrees minLat;
    CLLocationDegrees maxLat;
    CLLocationDegrees minLon;
    CLLocationDegrees maxLon;
    //解析数据
    for (int i=0; i<rows.count; i++) {
        NSDictionary *row = [rows objectAtIndex:i];
        坐标模型类 *item = [[坐标模型类 alloc] initWithJson:row];
        if (item.vehicleNo && [item.vehicleNo length]>0) {
            标注模型类 *annotation = [[标注模型类 alloc] init];
            annotation.coordinate = item.baiduCoordinate;
            annotation.item = item;
            [_mapAnnotations addObject:annotation];
            [_bMapView addAnnotation:annotation];
            [annotation release];
            
            if (i==0) {
                //以第一个坐标点做初始值
                minLat = item.baiduCoordinate.latitude;
                maxLat = item.baiduCoordinate.latitude;
                minLon = item.baiduCoordinate.longitude;
                maxLon = item.baiduCoordinate.longitude;
            }else{
                //对比筛选出最小纬度，最大纬度；最小经度，最大经度
                minLat = MIN(minLat, item.baiduCoordinate.latitude);
                maxLat = MAX(maxLat, item.baiduCoordinate.latitude);
                minLon = MIN(minLon, item.baiduCoordinate.longitude);
                maxLon = MAX(maxLon, item.baiduCoordinate.longitude);
            }
            
            [_carPointArray addObject:item];
        }
        [item release];
    }
    //动态的根据坐标数据的区域，来确定地图的显示中心点和缩放级别
    if (_carPointArray.count > 0) {
        //计算中心点
        CLLocationCoordinate2D centCoor;
        centCoor.latitude = (CLLocationDegrees)((maxLat+minLat) * 0.5f);
        centCoor.longitude = (CLLocationDegrees)((maxLon+minLon) * 0.5f);
        BMKCoordinateSpan span;
        //计算地理位置的跨度
        span.latitudeDelta = maxLat - minLat;
        span.longitudeDelta = maxLon - minLon;
        //得出数据的坐标区域
        BMKCoordinateRegion region = BMKCoordinateRegionMake(centCoor, span);
        //百度地图的坐标范围转换成相对视图的位置
        CGRect fitRect = [_bMapView convertRegion:region toRectToView:_bMapView];
        //将地图视图的位置转换成地图的位置
        BMKMapRect fitMapRect = [_bMapView convertRect:fitRect toMapRectFromView:_bMapView];
        //设置地图可视范围为数据所在的地图位置
        [_bMapView setVisibleMapRect:fitMapRect animated:YES];
        
    }

MKMapRect zoomRect = MKMapRectNull;
for (id <MKAnnotation> annotation in mapView.annotations) {
    MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
    MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0, 0);
    if (MKMapRectIsNull(zoomRect)) {
        zoomRect = pointRect;
    } else {
        zoomRect = MKMapRectUnion(zoomRect, pointRect);
    }
}
[mapView setVisibleMapRect:zoomRect animated:YES];