What is loop closure and how do I get it?

A loop closure is when the Paracosm SLAM software recognizes a place that it’s been to before. When it recognizes that place, it looks to see if there was significant drift between those captured locations. 

If there was significant drift, then it closes the loop and corrects the error throughout the entire scan. If there is no significant drift, then nothing happens

The difference

Why Loop Closure helps

Paracosm SLAM tracks the motion of the device as you walk around a space. The tracking is frame to frame, which means we track where you are going based on where you just were. This tracking is very accurate when in wide open spaces because there are many common features. 

When traveling long linear distances (city blocks or long winding interior hallways) you are always seeing new parts of the environment with new features so there are more opportunities for drift to accumulate.

Environments to scan in loops:

Any environment where you travel a long linear distance from your starting point, without seeing many common features, e.g.:

  • Long winding hallways
  • Multiple city blocks
  • Tunnels
  • Warehouses with dense rows

Note: In narrow areas, like a hallway, it may not be best to backtrack to close a loop. For these environments, it is best to scan shorter distances (no more than 300 meters at a time) and register them in software.

Environments where loop closure may NOT be needed:

Any environment where you frequently see similar features. This is commonly more open spaces, where even if you scan a long time, you are capturing the same features multiple times, e.g.: 

  • Open warehouses
  • Outdoor courtyard
  • Open floor plan office
  • Small compact indoor environment

How to use Loop Closure

The PX-80 detects loops using the geometric features captured by the LiDAR. To detect a loop, it needs to be in a similar position in an environment and have a similar field of view

  • At the start of the scan, hold the PX-80 vertical and still for 20-30 seconds before tilting the pole.
  • When looping back to your starting point, move very slowly and again hold the PX-80 in the vertical position.
  • Overlap from your starting point by about 15-20 seconds
  • Note: loop closure will not fix broken scans due to tracking loss. When moving the PX-80 into new areas (rooms, doorways, hallways), moving slowly will improve the tracking quality. Try to scan smoothly, moving slowly when turning around or taking corners.