VLX appears to get lost during some scans

From time to time during a mapping operation the VLX appears to get lost/lose it's reference. This has happened when scanning tight to semi tight spaces such as tunnels. In the attached image you will see two shafts. These shafts are approximately 250' apart. During the scanning operation I noticed that though I was moving (slowly) the VLX user interface showed the VLX icon moving static like in the same place. The walls of the tunnel had many features that differed throughout the alignment.   I canceled the scan and performed a second scan. Though the second scan provided better results, the postprocessed data was off in total length. Is there a best practice that I can employ to avoid the VLX from becoming confused in terms of its' location in space. 

Hi Jason,

thanks for using our forum! (btw we moved your request from IVION to the M6/VLX section)

Tunnel mappings are always the most difficult situations for the system. Through your description there seemed to be indeed a SLAM lost when you noticed the VLX icon staying static in the screen, and a sensible decision to have a retake after noticing.

However, I'm not really sure of the features effectiveness in the tunnel. Just from the quality map it looks there are features, but in a repeated manner every 2-3 meters. This could be easily also a confusing environment for the SLAM. A specific feature is for example a barrel on the current point and after a few meters a chair (another unique feature) etc. 

In the post-processing stage, you can also try to select the outdoor preset for processing, this might also help to correct the original mapping's SLAM break.

I hope the above points can help to some extent. If you would like to deeper investigate on this mapping data, we can also move on to a support case. There we could check deeper with your original data, processed data etc. to see if there's anything to tweak in mapping and processing.

Best, Youlin

Thank you Youlin.

One of my scans is very disaligned. There was a lot of high grass and trees. so the slam made a mess. the buildings are doubles etc.

Is there anything that can be done in a case like that ?