Application | Drone LiDAR survey planning with UgCS

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UgCS: Flight Planning & Control
October 16, 2023

The UgCS toolset for LiDAR mission planning is currently enabled for UgCS EXPERT and UgCS ENTERPRISE licenses and for supported DJI, Ardu, and PX4 drones. To use the LiDAR toolset - create a new route in UgCS.

Overview

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:
  1. Eight figure
  2. U-figure
  3. IMU calibration segments for DJI L1, L2
  • Flight patterns for route planning:
  1. LIDAR Area
  2. LIDAR Corridor
  3. Pattern calibration (within mission)
  • The preset drone turns:
  1. Bank turns
  2. Loop turns
  • AGL (above ground level) and AMSL (above mean sea level) line spacing

Let’s see in more detail how it works.

Content

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
  • U-shape
  • DJI L1, L2 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.

Parameter Definition
Speed, m/s The horizontal speed of the drone, m/s
Width, m Width of the bounding box of the figure. Default: 30 meters
Length, m Length of the bounding box of the figure
Altitude, m Altitude above elevation in the figure center
Direction angle Specifies the azimuth of forwarding passes (you can turn figure)
Number of passes The number of passes the drone should execute in the pattern

 

Figure 1. U-figure turn

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.

Parameter Definition
Speed, m/s The horizontal speed of the drone, m/s
Width, m Width of the bounding box of the figure. Default: 30 meters
Length, m Length of the bounding box of the figure
Altitude, m Altitude above elevation in the figure center
Direction angle Specifies the azimuth of forwarding passes (you can turn figure)
Number of cycles Number of cycles

 

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.

These blue lines indicate the route segments where calibration will be performed.

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:

Parameter Definition
FOV Field of view of the LIDAR, degrees
Altitude mode AGL - Above Ground Level means that the drone will follow the digital elevation model.
AMSL - Above Mean Sea Level means that the drone will fly straight at a constant absolute altitude.
Flight height, m Altitude in meters which depends on the altitude mode
Line spacing
  • Side overlap, %
  • Side distance, m
There are 2 options. A pilot can specify side overlap in percent or side distance in meters

In case of percentage, software will calculate line spacing based on FOV and flight height
Flight speed, m/s Speed of the drone
Camera List of preconfigured profiles of cameras (optional)
Direction angle Specifies the azimuth of forward passes. Available only for Area. Hidden for the corridor
Double grid A checkbox. If checked then the trajectory is double grid, otherwise single grid (snake)
Turn type
  • Adaptive bank turn
  • Stop & turn
Loop turn angle, degrees The maximum value below which software will add loops for turns.
For values greater than “Loop turn angle,” standard bank turns will be used.
Range for the value: (0;180)
  • Default: 90
Straight flight after turn, m For LIDARs, it is crucial to have at least X meters of straight flight after each turn before entering the next segment.
Default: 10 meters
Corner radius Radius of adaptive turn
Area buffer Extends scanning in all directions by a specified amount of meters*

*Available only for LIDAR Area
Overshoot Extends forward pass for a specified amount of meters. Overshoot gives a drone some space to make a turn and return to the scanning area as straight as possible.

In case of corridor overshoot applies only to turns between parallel passes in a multipass mode*

*Available only for LIDAR Area
Overshoot speed Drone velocity for overshoot segments*

*Available only for LIDAR Area
Action execution How to execute actions:
  • Every point
  • At the start (segment start)
AGL Tolerance Allows to minimize number of synthesized waypoints, generated to keep constant altitude above the terrain. The bigger value, the fewer waypoints are generated
Avoid obstacles
No actions at last point Do not trigger camera after the last point if the segment

 

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:

Figure 2a. Line spacing calculation for AGL

Figure 2b. Line spacing calculation for AMSL

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).

Figure 3. The trajectory of the turn

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).

Figure 4. The trajectory of the loop turns

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.

Overshoot = 0
Area buffer = 0

UgCS LIDAR area buffer and overshoot

Overshoot > 0
Area buffer = 0

UgCS LIDAR area buffer and overshoot

Overshoot = 0
Area buffer > 0

UgCS LIDAR area buffer and overshoot

Overshoot > 0
Area buffer > 0

UgCS LIDAR area buffer and overshoot

 

  • DJI
  • YellowScan
  • Phoenix LIDAR
  • Riegl
  • LIDAR USA
  • GeoCue
  • Rock Robotic
  • GeoSun LIDAR
  • 3DT Scanfly
  • Topodrone
  • 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.

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