Live map doesn't look like it should

Introduction

Problem description

Sometimes during the scan, the live map will display double walls, misaligned structures such as columns, or even curved corridors and unclosed loops.

The algorithm running on NavVis devices is called simultaneous localization and mapping (SLAM), which maps the area and estimates the device’s motion. While you are mapping, the device is running a "lighter" version of SLAM capable of mapping in real-time. Therefore, these artefacts are sometimes visible due to the accumulation of small errors. During post-processing, the software has a "heavier" version of SLAM that creates higher quality maps. This heavier algorithm uses loop closures to recognize revisited areas and correct the map. This is how doubled features will be aligned and drift errors removed.

Scope

This solution applies to any version of NavVis Processing.

Troubleshooting procedure

1. Proceed with the scan normally unless there is a large sudden jump in the trajectory, as if the device teleported to a whole new area. This means that the SLAM got lost and you should terminate the mapping and continue from where you stopped (no need to remap the whole area). The small errors in live mapping will be corrected after you post-process your recorded data. 

2. If you still see errors after processing, please contact our support team at support@navvis.com and document your issue (attach quality maps from before and after processing and log files). In most cases, we will need your datasets_rec folder. If possible, zip it and upload to an online drive where the team will be able to access it. We will then try to rectify your data and send you back the results.