How can this loam build a completed map?

[jjrCN]

The finial output topic of the loam is "/laser_cloud_surround", but it is not a completed result of the input dag. The points in "/laser_cloud_surround" is only the nearest part of the intput lidar points. As the code below which is from the function "bool BasicLaserMapping::createDownsizedMap()", the points in "/laser_cloud_surround" is cleared every time.
// accumulate map cloud
_laserCloudSurround->clear();
for (auto ind : _laserCloudSurroundInd)
{
*_laserCloudSurround += *_laserCloudCornerArray[ind];
*_laserCloudSurround += *_laserCloudSurfArray[ind];
}

so, how can build a full and completed map?

[he-guo]

hello，have you solved this problem, I also encountered the same problem.