1 HOW MUCH DOES THE LIDAR PAYLOAD COST?
Phoenix Aerial offers multiple LiDAR payloads. Prices range from $85k to $250k depending on desired range and accuracy.
2 HOW DOES THE SYSTEM WORK?
Please view the following demonstration video:
3 HOW DOES PHOENIX AERIAL PRODUCE A REAL-TIME POINTCLOUD?
The technique we use to derive positions with centimeter level acuracy is called Real Time Kinematic Global Navigation Satellite System (RTK GNSS). This system uses the satellite signal's carrier wave in addition to the information content of the signal and relies on a single GNSS reference station to provide real-time corrections. Now what happens during short periods of GNSS outages? Enter the Inertial Navigation System (INS): the INS uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate the position, orientation, and velocity of the system. In order to combine the two systems, a very sophisticated algorithm operates on streams of noisy sensor data to produce a statistically optimal estimate of the system's position at any point in time. By fusing this information with the LIDAR data, a point-cloud is generated and visualized in real-time using Phoenix Aerial System's SpatialExplorer.
In case real-time corrections from the GNSS reference station are not available or longer outages prevent transmission of data to the rover, a third party software package called Inertial Explorer™ can still produce a precise trajectory in post-processing. Both types of trajectories (either generated in real-time from the navigation system or from Inertial Explorer™ in post-processing) can be fused with LIDAR data using Phoenix Aerial System's SpatialFuser, creating point clouds in LAS format.
4 WHAT ARE THE HEADING OPTIONS?
GNSS receivers can only compute position, velocity and time, but not the orientation of the sensor, which is needed to create a point cloud.
There are multiple strategies to solve orientation:
a) Use 3 GNSS antennas. When the offsets between antennas are known, the GNSS receivers can communicate with each other and figure out the orientation of the antenna array. This is rather complex and heavy, and when one antenna fails to receive sufficient satellite signals, orientation is lost immediately.
For this reason, Phoenix Aerial Systems only offers this option for customers with very special requirements.
b) Use a medium-grade inertial measurement unit (IMU), which can derive roll and pitch angles by measuring the direction of gravity. Unfortunately, heading cannot be measured, as its rotational plane is perpendicular to gravity (you cannot feel a change in gravity when you yaw). After the GNSS-based position is computed, the unit is moved, so that the resulting trajectory of GNSS antenna and IMU can be aligned, thereby solving the heading. This is called kinematic alignment. There are some restrictions that might be difficult to obey with a UAV, e.g. the vehicle must move forward in a very straight line with a minimum speed, and vibrations must be kept to a minimum.
This can be a cost-effective option when the UAV supports kinematic alignment, or alignment can be done on the ground (e.g. on a car).
c) Use a high-grade IMU and keep the system static. The IMU can then feel the earth rotate and use this information to derive its orientation. This works well in vibration-free scenarios, but takes time. Also, some vehicles (e.g. ships) cannot support a totally static initialization.
This option works, but requires patience, which can become a problem in the field.
d) Use an IMU (medium or high-grade) and a second antenna. The IMU is used to derive pitch and roll angles, the second antenna is used to compute heading. This is the most robust setup: alignment works in static and mobile scenarios and on vehicles exerting more vibrations. When reception in one or both antennas fails temporarily, the IMU can still support an accurate position and orientation for some time.
In our experience, this is the most reliable setup, and customers are usually very happy to have chosen this option.
5 TO WHAT KIND OF UAV CAN THE ROVER BE ATTACHED?
In principle, the Rover can be attached to any UAV capable of lifting 6kg payload and supplying sufficient power. In practice, helicopters (both single- and multi-rotor) are a very good fit, because of their safety and maneuverability.
Single-rotor gas-powered helicopters are often used because of their endurance: maximum flight-times between 45 and 90 minutes are a perfect fit for mapping of larger areas. Because of our Rover's dual-antenna setup and our customizable vibration dampeners, the comparably strong vibrations exerted by the helicopter's motors can be tolerated in most cases. However, airlines usually decline to transport machines that smell of fuel, which, combined with the weight and size of gas-powered helicopters, makes them hard to ship.
Electric multi-rotors feature flight-times of only about 25 minutes, which is plenty of time to map. Furthermore, the UAV can be transported much more easily: in most cases, it will pass as check-in luggage. Some UAVs with more than 4 rotors offer redundancy, so that the equipment is not lost when a single rotor collides. With some insurers, this can translate to lower insurance rates.
Fixed-wing UAVs can be suitable, but are constrained in terms of flight paths. For scanning of flat terrain or linear structures like pipelines or powerlines, they still are a great fit.
Please contact us for further information regarding UAV integration.
6 DO YOU INTEGRATE OTHER SENSORS, TOO?
Yes, we can integrate
- digital cameras (compact & DSLR with APS-C, full-frame and larger sensors) for orthophotos
- hyperspectral cameras (e.g. NDVI)
All sensor data is precisely time- and georeferenced.
7 WHICH 4G NETWORK CARDS WILL WORK WITH YOUR UNITS?
To have the rover connect to the internet, retrieve real-time corrections and stream a real-time point-cloud and status, we recommend to use a 4G interface card, which is plugged directlyinto the rover using a USB connection ("USB tethering").
The following paragraph lists devices that we have used successfully. Theoretically, an over-the-air firmware-update issued by the wireless network provider can change the compatibility status of each device, but we have not seen that happen so far.
Netgear AirCard 781S
Sierra AirCard 782S Mobile Hotspot
Sierra AirCard 760S
Sierra AirCard 763S
NovAtel/Verizon Mifi 4620L
Huawei MiFi MF 190
Netgear 340U / AT&T Beam
Novatel Wireless MiFi USB620L
Telstra 4GX USB+WI-FI plus
Devices known to NOT work:
- Verizon Jetpack 890L
- Huawei E8278s-603
- Telstra Mobile Wi-Fi 4G Advanced Pro X
- NetGear AirCard 770S