Looking at the top right corner of the image on the left, one can see two different outlines for the same building. This is caused by drift during the data collection from the first time you pass see the building (green section of the trajectory) and the second time you pass the scan (orange section of the trajectory). Kaarta has an automated loop closure tool that can be applied if:
- The position at the end of the data collection is close to the same position where the scan was started
- The drift occurs over the entire data collection and not the result of an instantaneous twist
To minimize this drift, you can change the data collection method to overlap areas sooner, or avoid overlapping the area altogether. If the total drift between scan sightings is less than a quarter meter or so, Kaarta’s algorithms will close the gap automatically to prevent the double registration, but does not back-correct the data. This prevents the drift from propagating and limits the overall error due to drift.
Kaarta is working on a tool that can correct for drift, including instantaneous twists as well as address pointclouds that were collected with different start and stopping locations.
If you are interested in collecting datasets over longer distances, Kaarta sells Stencil which improves drift to around 0.2% of distance travelled without overlapping trajectories.