//根据polyline设置地图范围

- (void)mapViewFitPolyLine:(BMKPolyline *) polyLine {

    CGFloat ltX, ltY, rbX, rbY;

    if (polyLine.pointCount < 1) {

        return;

    }

    BMKMapPoint pt = polyLine.points[0];

    ltX = pt.x, ltY = pt.y;

    rbX = pt.x, rbY = pt.y;

    for (int i = 1; i < polyLine.pointCount; i++) {

        BMKMapPoint pt = polyLine.points[i];

        if (pt.x < ltX) {

            ltX = pt.x;

        }

        if (pt.x > rbX) {

            rbX = pt.x;

        }

        if (pt.y > ltY) {

            ltY = pt.y;

        }

        if (pt.y < rbY) {

            rbY = pt.y;

        }

    }

    BMKMapRect rect;

    rect.origin = BMKMapPointMake(ltX , ltY);

    rect.size = BMKMapSizeMake(rbX - ltX, rbY - ltY);

    [_historyMapView setVisibleMapRect:rect];

    _historyMapView.zoomLevel = _historyMapView.zoomLevel - 0.3;

}