UIimage图片失真


图中我的位置图标失真以下是代码
- (void)mapView:(MAMapView *)mapView didAddAnnotationViews:(NSArray *)views
{
    MAAnnotationView *view = views[0];
    
    // 放到该方法中用以保证userlocation的annotationView已经添加到地图上了。
    if ([view.annotation isKindOfClass:[MAUserLocation class]])
    {
        MAUserLocationRepresentation *pre = [[MAUserLocationRepresentation alloc] init];
        pre.fillColor = [UIColor colorWithRed:0.196 green:0.196 blue:0.196 alpha:0.15];
        pre.strokeColor = [UIColor colorWithRed:0.196 green:0.196 blue:0.196 alpha:0.8];
        pre.image =  [self reSizeImage:[UIImage imageNamed:@"gps_me"] toSize:CGSizeMake(21, 49)];
        pre.lineWidth = 1;
//        pre.lineDashPattern = @[@6, @3];
        
        [_mapView updateUserLocationRepresentation:pre];
        
        view.calloutOffset = CGPointMake(0, 0);
        view.canShowCallout = NO;
        self.userLocationAnnotationView = view;
    }
}- (UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize{
    UIGraphicsBeginImageContext(CGSizeMake(reSize.width, reSize.height));
    [image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];
    UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return reSizeImage;
}
试过@2x不行，用更大分辨率的图片也不行