To get accurate LiDAR scan results, a pilot needs to follow a few rules:
- Calibrate IMU (Inertial Measurement Unit) properly
- Maintain correct flight height and line spacing between scans to ensure coverage and point density
- Ensure the right drone turns and line scanning to minimize IMU error accumulation and excessive shaking of LiDAR above the area of interest
It is challenging to perfect every detail in manual flight mode, and even more so with flight planning tools designed for photogrammetry surveys. UgCS LiDAR toolset by SPH Engineering unlocks the full potential of LiDARs, making remote sensing the most effective with no human errors:
- IMU initialization patterns as drone commands:
- Eight figure
- IMU calibration segments for DJI L1
- Flight patterns for route planning:
- LIDAR Area
- LIDAR Corridor
- Pattern calibration (within mission)
- The preset drone turns:
- Bank turns
- Loop turns
- AGL (above ground level) and AMSL (above mean sea level) line spacing
Let’s see in more detail how it works.
IMU (Inertial Measurement Unit) calibration is typically performed at least two times per flight. Before scanning begins and after scanning ends. Optionally, the pilot may pause the flight and perform an additional IMU calibration to reset accumulated errors. The calibration can be performed manually or using an automated IMU calibration command within UgCS.
Different LiDAR manufacturers recommend different calibration patterns. UgCS does support the most popular calibration patterns:
- Eight figure
- DJI L1 calibration (back and forth)
The main goal of the calibration pattern is to put drones to their maximum capacity in terms of roll angle. This means the figure must be executed at the highest possible speed to properly calibrate the IMU.
To add the figure, the pilot can click on the map to specify a center and an altitude and then the width, length, speed, altitude, and direction angle of the turns.
Input parameters are very similar to eight-figure. However, the generated trajectory is different. The drone makes several passes back and forth and then makes a U-turn (Figure 1).
When the drone (M300, M600, M210, M200) is connected to UgCS, the "Pattern" button will be available in the "Commands". To add the figure, a pilot specifies turns' width, length, speed, altitude, and direction angle.
DJI recommends performing a back-and-forth pattern every 100 seconds or every 1000 meters during the flight mission (whichever comes first). This pattern is added automatically by default to LiDAR Area and Corridor missions. It can be added/removed by checking/unchecking the “IMU Calibration” checkbox in the route segment settings.
There are two different LiDAR survey segments in UgCS:
- LiDAR Corridor
- LiDAR Area
LiDAR area scanning is helpful for the following: construction sites, open-pit mines, power stations, landfills, archeology, and forestry.
The pilot has to specify the following:
- Area boundaries as a polygon
- Flight height AGL or AMSL
- LiDAR sensor FOV (field of view) angle
The area can be divided into the following trajectories:
- Single grid
- Double grid
LiDAR corridor scanning is helpful for the following applications: roads, power lines, and pipelines.
The corridor can be divided into the following trajectories:
- Single pass - along the corridor center line
- Multiple passes to cover a certain corridor width with scans of a certain lateral overlap
In the case of corridor geometry, a user specifies a centerline and width.
Besides the general trajectory shape, pilots input the following:
The FOV should always be specified manually by the pilot. The general assumption is that a drone always flies at altitudes lower than the LiDAR range; i.e. the pilot defines FOV and altitude independently. These parameters affect line spacing.
Line spacing is calculated differently for AGL and AMSL modes:
SW (Scan Width) = 2*H*tan (FOV/2)
Line Spacing (Side distance) = SW*(1-Side Overlap Percentage)
The quality of LIDAR data is greatly influenced by the way drone makes turns. The most important thing is to reduce the shaking of the sensor and follow the trajectory as accurately as possible.
The turn should look like a normal bank turn for angles bigger than “Loop turn angle” degrees (Figure 3).
The radius of the bank turn should be as specified in the “Corner radius.”
For angles less than or equal to “Loop turn angle” degrees, turns may look like a loop maneuver (Figure 4).
Important: after the loop turn, before entering the next segment, the drone should fly “Straight flight time after turn” seconds straight.
Loop turns do not apply to turns in overshoot segments. In case of overshoot turns, a bank pattern applies.
By default, trajectory and LIDAR footprint are assumed to be inside the corridor or area.
An area buffer applies to all flight areas to improve coverage on borders by extending the original shape.
Overshoot extends forward passes to make turns outside of the main trajectory.
- Phoenix LIDAR
- LIDAR USA
- Rock Robotic
- GeoSun LIDAR
- 3DT Scanfly
- Balko Tech
UgCS LiDAR toolset is currently supported for DJI M300, M350, M600, M210/200, drones, Freefly Alta X, Freefly Astro, Inspired Flight and other Ardu and PX4-based vehicles.
The new LiDAR functionality is available on the UgCS EXPERT and UgCS ENTERPRISE license types.