Visual position or line of sight is utilized by a pilot to figure out the position and orientation of the drone and hence to maneuver in accordance to his requirement and preference. Drones equipped with advanced technology are fitted with GPS receivers within the navigation and control loop that allow for some state of the art GPS navigation systems that include:
- Position Hold: the drone is able to retain its fixed position and elevation
- Return to home: In case the battery runs out of juice, the connectivity between the drone and the radio controller becomes attenuated or the pilot presses the return to home button, the drone comes back directly to its designated home station
- Autonomous flight: GPS waypoints are established and the flight path of the drone is programmed by the pilot beforehand. The drone follows this pre-destined path while the autonomous flight feature is triggered on
These features require the GPS system to work so fundamental knowledge and understanding of the GPS system is essential to a drone pilot.
GPS Drone Navigation
The Global Positioning System is a navigation system guided by satellites. The radio receiver that comes with a drone receives signals from the orbiting satellites to figure out the position coordinates, speed and time of the machine. This navigation technology is more accurate in contrast to other navigation technologies out there and provides precise information regarding the position of the drone accurately up to a few meters. More advanced GPS technologies can provide information regarding the position of a device accurately within a few centimeters. As integrated circuits have become more and more compact in size, GPS navigation systems have become more and more affordable and accessible to everyone. Since GPS is a broadcast radio system, so it can be accessed from anywhere on the earth.
The GPS system was developed by the US military way back in 1973 in order to predict and program the trajectory of Inter-Continental Ballistic Missiles. Awareness about the target was always going to be easy but as far as the US military is concerned, since most of their nuclear warheads were being carried on submarines, so knowledge about the exact location of the launching vehicle was of prime importance. So, in order to ensure that the nuclear warhead was able to hit the target accurately, the knowledge of missile launching vehicle was required. This led to the development of the GPS system.
GPS Position Triangulation
GPS system uses a mathematical concept of triangulation in order to determine the exact coordinates of an object. Triangulation is a process in which the position of the radio receiver is figured out by determining the radial distance of the received signal from a number of sources.
The satellite GPS system utilizes trilateration that makes use of four signals to determine the position of the GPS drone receiver. The signal from one satellite lets the pilot figure out that he or she is on a sphere at a certain radius from the satellite. A second signal is also considered as a radial distance with the receiver on the second sphere and it intersects the first signal. This forms a circle that intersects both the spheres. Another signal helps in pinpointing the location down to two points on the circle.
A fourth signal is used to narrow down the location from the two points. Generally one of the two points are discarded with the proposition that one of them is either situation too far from the earth or is moving at an implausible speed. Fourth signal is traditionally used but for some other purpose.
Distance from time
A GPS receiver is supposed to be able to measure the accurate distance of the signal received by the three or four satellites. Each satellite transmits an encoded signal that includes the time stamp and position of the signal. We all know the radio waves propagate at the speed of light. If the clock of the receiver is precise, we are well familiar with the common formula: distance = speed x time. Having said that, there is something wrong with this methodology.
The first issue is concerned with synchronized clocks. Each satellite has four atomic clocks, two cesium and two rubidium. They provide an accuracy of one second in 100,000 years. The receivers, on the other hand, have lesser accurate clocks and so have to compensate for the time taken by the radio waves to reach them.
It should be noted that radio waves propagate at the speed of light in vacuum while the radio waves and their trajectory are convoluted by the earth’s atmosphere and some latency is introduced. So, the receiver has to be programmed in order to allow for these shortcomings.
GPS Error Correction
If the receiver’s clock is synchronized with that of the satellite, then all the four radio waves from each of the satellite would intersect each other at one single point. The receiver is dependent on a single correction factor that it can apply to all the ranges so that they converge at one single location. This correction factor tends to synchronize the satellite’s clock with that of the receiver.
Having said that, knowledge about the distance of the receiver from the satellite is only one thing. We also need to know about the position of the satellite. Since the orbits of the satellites are designed expertly so it is possible to forecast about the next location of the satellite on its trajectory. Small scale trepidations can bring about undesired distortion in the path of the satellite but this can be cancelled out by carryout ground based calculations of the satellite’s orbit. All this time stamped information is transmitted by the satellite along with the signal.
The effect of the atmosphere on the radio waves and their path can be modelled and forecast by using different mathematical models. Effect of the charged particles in the ionosphere and troposphere are also taken into account in these calculations. The angle of each signal is also determined by the receiver as it is responsible for giving out the path length of the signal.
Military and Civilian GPS
As we discussed earlier, GPS was invented by the US military forces in order to give them unprecedented advantage over their competitors. It was considered that GPS signal could be beneficial for civilian use as well but if the civilians detected the same signal as the military, the military advantage that US was seeking could be cancelled out. So, two versions of the GPS were contrived. The Precise Positioning System was designed for military purposes while the Standard Positioning System was developed for civilian use. Standard Positioning System’s receivers were lesser accurate with Selective Availability adjustment. However, Selective Availability adjustment was discontinued in 2000 and the accuracy of the GPS system was enhanced for civilian usage as well. Ever since, the GPS has become more and more common among the civilians.
You must be acquainted with the GPS receivers used for car driving purposes. But as soon as you figure out your exact location on the ground, it unleashes new arenas for technological revolutions. Self-driving cars that make using of the GPS for navigational purposes are a reality now. Your car can be made more secure on the highway if your car knows about its location and that of the vehicles around it. This would ensure that any human error could be accounted for. Air traffic control is also benefitted from this technology. It is expected that GPS will eliminate the need for radar aircraft tracking systems in the days to come.
GPS is an extremely handy tool for emergency response squads as it provides the shortest and fastest possible route to the desired location. GPS is also being employed by farmers as it enables them to harvest higher yield of crops. GPS collars are also being put into use to track down pets, animals and wildlife. Talking GPS modules are helping people suffering from visual impairments.
Alternate GPS Systems
The US GPS satellites is one of the very many GPS systems prevalent worldwide. The GLONASS GPS satellites were launched by the Soviet Union in 1982 and are still being utilized by Russia. The Galileo GPS system is being planned to be deployed by Europe while China is in the middle of developing its Compass GPS satellites. India’s IRNSS and China’s BeiDou are part of the smaller GPS systems working around the world.
Conventionally, GPS receives signals from any one of the above mentioned satellite systems. But there is no reason that a receiver cannot receive signals from multiple GPS systems. The US GPS satellites have been distributed in such a way that at the very least, four satellites are always visible from any location around the world. The accuracy of position determination can be greatly enhanced by blending signals from GPS, GLONASS and Galileo and hence the distortion created by the skyscrapers can be greatly reduced. The larger the number of satellites from which a receiver can potentially get signals from, the higher the accuracy of figuring out the desired location. There are tons of modes integrated in drones that have the ability to use both the GPS and GLONASS satellites and hence provide far greater navigation than usual. This is a much sought after feature in modern day drones and you should always look for a drone that is able to get signals from multiple GPS satellite systems.
Issues and Challenges
Despite all the benefits and advantages associated with GPS system, there are few inbuilt lacunas. The GPS satellites have not been designed for eternity and ought to be replaced after completion of their expiry period. Space represents a hostile environment that can see the satellites being damaged by meteors and solar flares. Privacy and tracking are of vital importance when it comes to GPS systems since an individual or a certain vehicle can be spied upon using a GPS tracking system.
GPS Drone Navigation Waypoints
GPS drone waypoint navigation has been made possible with the inclusion of GPS receivers in the modern day drones. This feature lets the drone follow a pre-determined path autonomously. It also lets the drone know how fast, at what altitude and towards which destination, the drone is supposed to fly. It also can be programmed to hover over a certain location for specified duration.
Drones are being employed for building inspection, road repairs and maintenance and infrastructure surveys and examinations. They are also be used in the agriculture sector as well for inspection of farms and tracking down farm animals. The drone is instructed to inspect a certain location while following the preprogrammed route. The user on the other hand has to focus on controlling the camera and carrying out the inspection rather than worrying about flying the darn machine.
The utility and range of applications for which the drones can be put to use has increased exponentially with the development of GPS drone navigation waypoints system.