This article describes what the Hovermap LiDAR detects, and the factors that affect the quality of the point cloud. It covers sensor performance, point density, and the data recorded during a scan. For the conditions that limit safe operation, see Hovermap operating limitations.
LiDAR performance
Hovermap ST and Hovermap ST-X use different LiDAR types. The table below gives the performance of each.
Hovermap ST | Hovermap ST-X | |
|---|---|---|
Number of lasers | 16 | 32 |
Number of laser returns | 2 | 3 |
Laser range | 100 m | 300 m |
LiDAR field of view | 30° | 40° |
Number of points per second | Up to 300,000 (single return mode) | Up to 640,000 (single return mode) |
Hovermap field of view | 360° | 360° |
Point density
Point density is the number of points in an area. A quality scan needs knowledge of which areas receive the greatest point density, and of the conditions that reduce it.
Coverage and the blind spot
Hovermap has 360° coverage, but it focuses on some areas more than others. The area of greatest point density is directly in front of the LiDAR sensor, shown as a dark blue cone in the following image. A number of lasers always face this direction, even during rotation of the sensor head.
The rest of the sphere still has good coverage, but the point cloud in these areas is less dense. The remainder of the lasers are in constant motion, because the scanning head rotates.
A small blind spot exists behind the body of Hovermap, shown in gray in the following image. The body of Hovermap blocks the field of view in that direction. During a scan, account for any platform or person that holds Hovermap.
Dense forward cone and the blind spot behind the Hovermap body.
Surface type
Point density also depends on the surface. A highly reflective surface and a non-reflective surface both return fewer usable points than a textured surface. Water returns fewer points as it becomes clearer.
For the full list of surfaces that cause missing or noisy points, see Hovermap operating limitations.
Distance to the target
A shorter distance from Hovermap to the target gives greater accuracy, beyond the minimum scan distance of 0.5 m. A short distance to the target is more likely to give a clean point cloud on the first attempt, with less cleanup in the post-processing stage. Stay within 40 m of the target.
Improve point density
The factors above all have implications for use of Hovermap. In practice, visualize the cone of denser points as a flashlight. During a scan, focus the cone on each important feature to capture. The SLAM process then creates a denser, more accurate point cloud, and the risk of a SLAM slip decreases.
Hovermap records point data continuously. More time spent on the target area increases point density, even when the sensor cannot point directly at the area of interest.
Tips to improve point density
Move slowly.
Sweep the cone in all directions, to give denser point coverage.
Attach Hovermap to the drone or vehicle with the cone toward the largest number of features.
Captured data
The data captured by Hovermap includes characteristics such as range, intensity, and the time of capture. A mounted platform also lets the system embed GPS data into the collected LiDAR data. The post-processing stages can then use this embedded data.