Image: Septentrio
Avalanches can be a danger for skiers as well as for the resort towns that welcome them. For protection, towns erect steel fences to act as barriers along the ski slopes. But before these snow barriers can be built, steep rock faces and cliffs need to be surveyed.
Darnuzer Ingenieure AG, a Swiss-based surveying and mapping company, uses a drone with a built-in high-performance GPS receiver to survey these harsh areas in hours.
“Drones have made mapping workflows faster, safer and more efficient,” said Septentrio’s senior market access manager Gustavo Lopez. “GNSS technology has led to the evolution of post-processing kinematic (PPK) methods, which help make the photogrammetry process efficient and accurate.”
Every year, thousands of tourists visit Davos in the Swiss Alps. To protect the town and the skiers, avalanche barriers were built along the steep slopes. To plan the work along the uneven rock face, a detailed 3D reconstruction of the area was needed, but getting to the survey site would be a rock-climbing feat.
Darnuzer Ingenieure used the WingtraOne fixed-winged drone, which features a top-quality camera and a Septentrio high-performance GNSS receiver. A single surveyor took the drone to the rocky Parsenn slope during the summer season, capturing ground images — without snow — that were needed for the 3D model.
WingtraOne PPK enabled high-precision mapping without the need for ground control points. During the flight, each image was accurately time-stamped and raw GNSS data from the Septentrio AsteRx-m2 receiver was carefully logged.
Even in this mountainous region, where peaks obstruct the sky, the receiver delivered continuous positioning. The GNSS data was processed by the GeoTagZ software library, which used corrections from a nearby base station to generate real-time kinematic (RTK) centimeter-level positioning.
The GeoTagZ software library incorporated Septentrio’s core GNSS algorithms to assure the best positioning performance. Accurate positioning was then synchronized with the images in the next step of the post-processing workflow.
It only took Wingtra a few days to integrate the GeoTagZ library into its WingtraHub software package. Integration of GeoTagZ into WingtraHub simplifies mapping jobs for customers like Darnuzer Ingenieure.
“The beauty of this solution is that the drone benefits from the receiver’s high-quality raw measurements without the need for a real-time corrections link for accuracy,” Lopez said. “The quality of the measurements comes from the technology built into Septentrio’s receivers, which is designed to be resilient to radio frequency interference and multipath. In post-processing, the GeoTagZ software enables the most accurate positioning, thanks to its high-performance RTK engine.”