VSLAM ACCURACY AND DRAGONFLY PRECISION
Dragonfly, our Visual SLAM technology, provides high level of accuracy.
The “drift” is the location error accumulated over time during the simultaneous navigation and mapping of unknown environments (venues where Dragonfly has not been used before and thus for which there is not yet an existing 3D map like for example, the first time a forklift that makes use of Dragonfly is driven inside a warehouse). The drift can be expressed as a percentage:
- When using stereoscopic cameras the drift has been verified to range between 0.6% and 1.3%. This means that if you drive a forklift with Dragonfly installed on board along a 100 meters linear path, at the end Dragonfly will report a location with a ROC of 60-130 cm (the location could 60-130 cm away from the real location of the forklift).
- When using monocular cameras the drift in itself can be pretty high. The drift is high enough to NOT recommend relying on the location provided by Dragonfly engine in an un-mapped venue after 1 minute of navigation. This is why when Dragonfly is used with a monocular camera in an unknown environment it is mandatory to perform a pre-mapping of the entire environment with frequent loop closures (see below). After a pre-mapping of the venue, the ROC is usually 1% of the distance of the camera from the closest real-world reference (visual or virtual marker). For instance, in a 15,000 sqm warehouse, the average ROC is about 30 cm.
The drift of Dragonfly when used with monocular cameras (and also with stereoscopic cameras) is automatically corrected by Dragonfly each time there is a loop-closure.
A loop-closure is triggered each time the camera is moved from an area already mapped to an unknown area and then back to an area already mapped. When this happens Dragonfly corrects the location and the map is also updated. Loop-closures are the key to get the maximum accuracy when Dragonfly is used with monocular cameras.
It is strongly recommended to perform frequent loop-closures during the initial mapping, for both monocular and stereo cameras installations. A loop closure is triggered also when an existing map is fused with a new one (if the map fusion option is active inside the Dragonfly settings).
When navigating inside a known environment, when Dragonfly relocates the device inside a venue already mapped, the accuracy depends on the precision of the triangulation of known points (features). The radius of confidence, is typically 5-10 cm, and depends on several factors, including:
- The quality of the camera;
- The quality of the camera calibration process;
- The quality of the georeferencing process;
- The quality of the mapping process;
- The type of the environment:
- amount of objects/real-world reference (and thus features);
- availability/type of textures;
- dimension of the map.