Share | 03/05/2020
GCPs, RTK, PPK – Why are they so important?
A surveyor’s job is to capture accurate data. With boots on the ground, this responsibility is almost entirely up to surveyor and their level of expertise. However, developments in technology, like drones, have made the surveying process faster, safer and more efficient.
While laying ground control points (GCPs) has been a necessary step in drone surveying workflows from the beginning, advancements in GNSS technology have led to the evolution of real-time kinematic (RTK) and post-processing kinematic (PPK) methods. But like everything in life, there are pros and cons to each of these processes.
senseFly’s Drone Dictionary defines a ground control point as “a location or object on the ground that has precisely known coordinates”. GCPs are used to accurately geo-reference and align projects from relative accuracy—one to two meters—to absolute accuracy—two to five centimeters.
GCPs have been a proven method of accuracy for years, but with safer and faster methods available, it should be used only when RTK and PPK are not possible.
Real-time kinematic is a technique used to enhance the precision of position data derived from satellite-based positioning systems, which relies on a single reference station or interpolated virtual station to correct geotagged locations while in flight. In other words, RTK is a correction method that enhances GNSS precision.
The RTK methods works well in flat terrain where trees or mountains won’t get in the way of the communication signal. RTK is restricted by the power of ground and air communication with the drone. If there’s more than three kilometers between the drone and the ground station, or if there are obstructions such as trees or mountains, there’s a chance it will lose signal.
To use RTK, flights in open terrain and within two or three kilometers of the ground station is ideal.
An alternative method to RTK is post-processing kinematic. This kinematic technique corrects geotag accuracy after capturing and uploading drone data. The data is corrected in the flight data manager (FDM) and then processed in the cloud.
PPK has some similar pros and cons to RTK in comparison to GCPs because of the safety and efficiency these methods provide. The major difference is that the PPK method is ideal for longer flights, especially BVLOS missions. The longer the flight, the greater chance there is of losing signal to the connection needed for RTK.While it’s clear each method has its share of pros and cons, the big picture is the same: the integration of GNSS technology with the drone industry has helped improve the workflow of drone pilots. Its made their mapping missions more accurate, efficient, cost-effective and, most importantly, safe.
For more information about RTK and PPK technology for a senseFly fixed-wing drone, contact your nearest distributor here.
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