- How to design a flight plan for mapping an area using a low-cost multi-beam LiDAR mounted on a UAS platform and what are the input and output parameters?
- What is the expected point density in an urban region at different flying heights, sidelaps, and flying speeds using low-cost multi-beam LiDARs?
- Among the considered low-cost LiDAR sensors, which one is more efficient for mapping purposes in terms of coverage and point density?
2. Methodology and Developed Tool
- Swath width of the scan
- Number of flight strips
- Separation distance between flight strips
- Number and location of the flight waypoints
- Estimated point density
- Estimated flight duration
2.1. Flight Plan Design
- LiDAR specifications: Every multi-beam LiDAR sensor has its own geometric structure, which includes FOV, angular distribution of beams, angular resolution, output rate pts/m2, rotation speed, and the maximum scanning range. Table 1 shows the characteristics of the three selected low-cost multi-beam LiDAR sensors, as published by their manufacturers [35,36,37].
- Flight plan specifications: They include flying height H, flying speed m/s, and the required sidelap % between adjacent scanning strips. It should be noted that a larger overlap percentage ensures higher coverage but requires a longer flight time, which should be carefully considered.
- : project area dimensions defined as a rectangle with a length and width .
- flying height above the ground level.
- scanning range of the LiDAR.
- distance between two successive waypoints.
- : along track scanning width.
- : across track swath width of the scanning.
- : scanning field of view out of the offered 360° FOV.
- : separation distance between the flight strips.
- : number of flight strips rounded to positive infinity.
- number of waypoints per strip.
2.2. Scanning Simulation
- : the measured range distance from the LiDAR to the object points.
- : rotation matrix of the boresight angles.
- : the measured azimuth angle of the laser beam.
- : the vertical angle of the laser beam measured from the horizon.
- , and : the coordinates of the LiDAR sensor.
- and : the coordinates of the scanned point.
- Compute the scan vector from the LiDAR to the object direction point . This vector might intersect the simulated object before or after at (Figure 5).
- Define the object plane normal by the parameters.
- Compute the vector = Dot product), which should be a non-zero value if the LiDAR beam line and the object plane are not parallel and should intersect at a unique object point .
3. Results and Discussion
3.1. Flight Planning Tool
3.2. Estimated Average Point Density
3.3. UAS LiDAR Mapping of an Urban Area
- In contrary to the image-based UAS missions, even with the nadir orientation of the LiDAR, a significant coverage and point density on building facades could be attained.
- M8 had a higher performance than VLP-16 LiDAR and OS-1-16, especially on facade features.
- Density achieved on facades was approximately half the density achieved on the ground and roof features.
- Ouster OS-1-16 slightly outperformed the VLP-16 LiDAR on the ground and facades.
- The density achieved on facades was better at the high altitude parts than the lower altitude parts.
- Sample the reference model as a point cloud with a uniform spacing of 10 cm.
- For every point in the reference point cloud, find any scanning point within a 25 cm search radius.
- Label reference points as “covered” if they have a neighboring scanned point, or “uncovered” if there are distant scanned points (≥25 cm).
- Use the “uncovered” points as an indicator of completeness.
3.4. UAS LiDAR Mapping of a Communication Tower
Conflicts of Interest
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|LiDAR Sensor/System||Velodyne ||Quanergy ||Ouster |
|Max. Range||≤ 100 m||> 100 m @ 80%||≤ 120 m @ 80%|
|Range Accuracy 1σ||±3 cm (Typical)||±3 cm||±1.5-10 cm|
|Output rate pts/sec.||≈300000||≈420000 (1 return)||≈327680|
|FOV - Vertical||≈30° (±15°)||≈20° (+3°/–17°)||≈33.2° (±16.6°)|
|Rotation rate||5-20 Hz||5-20 Hz||10-20 Hz|
|Vertical resolution||V:2°||V:3°||V: 2.2°|
|Horizontal resolution||H: 0.4°@ 20Hz||H: 0.14°@ 20Hz||H:0.35°@ 20Hz|
|Weight||830 g||900 g||425 g|
|Power consumption||8 w||18 w||14-20 w|
|Speed @ 10 m/s||Speed @ 5 m/s|
|LiDAR Type||Density pts/m2||Lack of Coverage|
|VLP-16||162 ± 62||11.1 %|
|OS-1-16||184 ± 70||8.2 %|
|M8||235 ± 93||7.6 %|
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