RECON UAV Acquisition

If you are using a Recon, the Recon Quick Start Guides include best practices which are helpful to review.

General Best Practices:

• Use only the supplied USB stick. The RECON hardware requires USB sticks with minimum write transfer speed, many other USB sticks can not write data fast enough, causing data corruption.

• Ensure you always remove the USB stick safely from your computer, and re-format it regularly using the RECON’s web UI.

• To avoid problems in postprocessing, ensure IMU-to-antenna offsets and IMU rotation are correct before acquisition.

• Wait for the camera to trigger two/three times and appear in the GUI before starting 'Data recording'.

If the camera has not appeared on the status page within two minutes, it may have been a cold-startup. In this case, restart the Recon and ensure that the camera appears in the GUI after initializing.

• At the very beginning and end of acquisition, leave the system acquiring data while static for at least 30 seconds.

• Ensure good GNSS reception and free sky during kinematic alignment and figure 8 maneuvers.

• Capture at least GPS+GLONASS data from a close-by reference station at 1-20 Hz, covering all of the rover’s acquisition. There’s no need to stream data from reference station to RECON during flight.

• The “Field of View” setting merely saves the given values as a processing preset, all data is still recorded with any FoV setting.

• If using SpatialExplorer, replay data to ensure LiDAR and camera coverage is sufficient before leaving.

Aerial Best Practices

Recon flight planning is a little different from the flight planning found in traditional PLS LiDAR systems. Very little can be changed in regards to the LiDAR system itself so all the changes need to be made to the flight characteristics of the aircraft, flight planning, and operational best practices.

First we need to understand the LiDAR in order to create appropriate flight plans. The system is a Hesai XT32 Puck Lidar that has a horizontal FOV of 106 degrees and a forward FOV of 15 degrees and aft FOV of 16 degrees. See example below.

Recon-XT FOV

For planning purposes, we will only be concerned with the horizontal FOV. PLS recommends planning all LiDAR acquisitions at a FOV of no greater than 90 degrees. By planning at 90 degrees we are creating a buffer zone for our LiDAR that accounts for unforeseen environmental conditions that could otherwise cause “gaps” in our coverage. Using the 90 degree FOV also provides a secondary benefit for mission planning, this creates an equilateral right angle triangle which dictates that the altitude and the lateral strip separation are the same if planning a 50% overlap, which is the PLS recommended overlap for UAS LiDAR acquisition. See example below.

90 degree FOV and 50% Overlap

So, if our flight plan has us at an altitude of 80 meters we will have a lateral strip separation of no more than 80 meters. But, we must also take into account the FOV of the camera which is narrower than that of the LiDAR. To prevent lack of coverage between photos we need to set our lateral strip separation closer than 80 meters. The easiest way to solve this is through the PLS Flight Planner software. In Flight Planner, each aspect of the sensor is taken into account when determining the optimal strip separation.

In this case, the camera has a narrower FOV than the LiDAR and Flight Planner accounts for that by using a tighter lateral strip separation. After calculating a flight in Flight Planner we see a recommended flight line spacing of 58.75 meters. We can check this by using the Ground Sampling Distance (GSD) PIX4D calculator. Using the Sensor width (mm), Focal Length (mm), Flight Height (m), and image width & height (pixels) we get a width of a single image footprint that is 118 meters across. Dividing this in half we get a lateral strip separation of 59 meters, confirming what was calculated by Flight Planner. See example below.

Camera Specs

GSD Calculator

Now that we know how to calculate lateral strip separation we can determine the ideal altitude for LiDAR acquisition. PLS validates all Recon XTs at 70m AGL with a speed of 8m/s using a “double” grid pattern. We do this because at this altitude and speed we are using approximately 90% of the LiDARs capabilities and producing a point cloud density that is good for our internal validation testing. Depending on the reflectivity and size of the object(s) you wish to capture will greatly influence the altitude and speed you fly. A good rule of thumb is to plan your flight altitudes depending on the minimum reflectivity within the target area or Area Of Interest (AOI).

The smaller and less reflective the target the closer to the target you will need to fly to get adequate returns/ echoes. If you intend to capture power lines for instance, lowering your altitude could, in theory, greatly increase your chance of capturing the powerlines in your data. Below are a few predetermined altitudes and speeds with their associated Points Per Square Meter (PPSM).

Recon-XT	Altitude	Air Speed	Flightline Spacing @ 50% sidelap	Nominal Point Density (NPD)
	70 m	8 m/s	50 m	181 PPSM
	70 m	6 m/s	50 m	241 PPSM
	60 m	6 m/s	44 m	282 PPSM

Next is planning your flights, PLS covers this subject extensively in our User Manual here.

PLS also offers Best Practices for Flight planning here.

Integrating the system to your aircraft is very simple and PLS offers a handy Quick Start guide for both the DJI M300 series of drones and the FreeFly Astro sUAS. Those quick start guides can be found here. If you are integrating into a different aircraft please feel free to contact PLS for help.

If you have any further questions or concerns please feel free to contact PLS Customer Support here.