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UgCS for drone-based LiDAR missions

UgCS for drone-based LiDAR missions

The UgCS toolset for LIDAR mission planning currently is enabled for UgCS ENTERPRISE license and for supported DJI drones. To use the LIDAR toolset - create a new route for DJI M600, M300 or M210/M200.

Overview

LIDAR (Light Detection and Ranging) is gaining popularity with professional drone surveyors. However, to get accurate LIDAR scan results, a pilot needs to follow a few rules:

  • Initialize IMU 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

Making everything right is impossible in a manual flight mode and extremely hard with flight planning tools tailored for photogrammetry surveys. UgCS LIDAR toolset by SPH Engineering unlocks the full potential of LIDARs making remote sensing most effective with no human errors:

  • IMU initialization patterns as drone commands:
    • Eight figure
    • U-figure
  • Flight patterns for route planning:
    • LIDAR Area
    • LIDAR Corridor
  • 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 all these things work.

Contents

 

IMU Initialization

IMU initialization is typically performed at least two times per flight. Before scanning begins and after scanning ends. Optionally, the pilot may pause the flight and make additional IMU initialization to reset accumulated errors. This is why we implemented this function as a drone command so that the pilot may run it at any time. For this command to run, the drone should already be in the air.

Different LIDAR manufacturers recommend various patterns. In UgCS, we support the two most popular: eight figure and U-figure.

 
 

Eight figure

The main goal of the calibration pattern is to put drones to their maximum capacity in terms of roll angle. That literally means that a pilot wants to pass the eight figure at the maximum possible speed, which will make a proper IMU calibration.

To add the figure, a pilot clicks 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 cycles Number of cycles
 

U-figure

U-figure turn
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).

To add the figure, a pilot clicks 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 cycles Number of cycles
 

Flight planning techniques

LIDAR survey typically employs the following patterns:

  • Corridor
  • Area

Drones can be equipped with either LIDAR or LIDAR and a Photo Camera. In the latter case, we must consider the FOV of the LIDAR and the FOV of the camera and choose the smallest one.

Scanning the area of interest

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
  • Effective scanner FOV (field of view)

The area can be divided into the following trajectories:

  • Single grid
  • Double grid

Scanning the corridor

LIDAR corridor scanning is helpful for the following: roads, power lines, and pipelines.

 

 

The corridor can be divided into the following trajectories:

  • Singlepass - along the corridor center line
  • Multipass 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.

Common input parameters

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
 

Field of view and line spacing

The pilot always specifies FOV manually. 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:

Line spacing calculation for AGL
Figure 2a. Line spacing calculation for AGL
 

UgCS for LIDAR Line spacing calculation for AMSL

Figure 2b. Line spacing calculation for AMSL

 

SW (Scan Width) = 2*H*tan (FOV/2)

Line Spacing (Side distance) = SW*(1-Side Overlap Percentage)

 
 

Turns

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 trajectory of the turn

Figure 3. The trajectory of the turn

The radius of the bank turn should be as specified in the “Bank turn radius.”

For angles less than or equal to “Loop turn angle” degrees, turns may look like a loop maneuver (Figure 4).

The trajectory of the loop turns
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.

Area buffer and overshoot

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

 

Supported LIDARS

  • DJI

  • YellowScan

  • Phoenix LIDAR

  • Riegl

  • LIDAR USA

  • GeoCue

  • Rock Robotics

  • GeoSun LIDAR

 

UgCS LIDAR toolset is currently supported for DJI M300, M600, M210/200 drones.

 

The new LIDAR functionality is available for UgCS EXPERT and UgCS ENTERPRISE license type.

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