What is a drone survey?
A drone survey is a survey performed from the air using a drone .
During the drone survey, heavily overlapping photos are recorded. These are then combined to create a georeferenced orthomosaic. The composition is done using photogrammetry software, the entire process being referred to as photogrammetry. The recordings must be very precise so that no inaccuracies result. A tachymeter is able to record measuring points. The drone also "only" takes measuring points, but in millions of times. This means that some of the point clouds even have to be thinned out. The large number of recordings enables the creation of a 3D model. In this way, the size of buildings can be determined and measured.
What level of accuracy can drone surveys achieve?
Drones for surveying can create surveys with different levels of accuracy depending on the needs of the project. In an independent study by Drone Deploy , the DJI Phantom 4 RTK achieved a relative vertical accuracy of 2 cm and a relative horizontal accuracy of 1.20 cm. For other tasks that require high absolute accuracy, there are drones equipped with RTK (Real Time Kinematic) and PPK (Post Processed Kinematics). In combination with some Ground Control Points (GCPs), drone surveying achieves higher accuracy.
What results does photogrammetry provide?
A special process is used to create the 3D model: photogrammetry. This allows digital twins of buildings to be created. Georeferencing is used during data collection to represent all sizes to scale. The so-called point clouds, with which the 3D models can be created, are used for this purpose. Once the creation is complete, the 3D model is saved in the form of a file. The format can be read out and processed with CAD or BIM (Building Information Modeling) software, for example.
Orthophotos and their advantages in detail
With the help of georeferencing, detailed and geometrically accurate maps can be created from aerial photographs. This option is primarily used in urban planning and development. In the past, airplanes or even satellites were used to create up-to-date orthophotos. The fact that the costs for this are hardly in a manageable range does not have to be mentioned separately. The use of a drone ensures that costs can be significantly reduced. Drones provide another decisive advantage for orthophotos: In contrast to airplanes, satellites and helicopters, they can fly at a lower altitude and thus provide a higher level of detail in the orthophotos. Although more images must be recorded during drone surveys to create an orthophoto,
Orthophoto of a photovoltaic system
Multiple sensors increase the accuracy of 3D modeling and orthophotos
In the leisure sector, the various models are often equipped with fewer sensors than is the case in the professional sector. Sophisticated optical sensors are used here to also be able to detect obstacles. Some recreational drones are also equipped with GPS and can therefore fly flight routes, but the equipment of a professional drone goes a few steps further. In addition to an RGB camera, a thermal imaging camera can also be used if thermographic recordings are required. Drones are designed and equipped specifically for surveying with so-called RTK-GPS sensors (Real Time Kinematic). This results in accuracies of one to two centimeters and a resolution of < 1cm/pixel and below for orthophotos.
With drones that are not equipped with RTK sensors, an accuracy of five to ten centimeters can be achieved. The possible use of a surveyor with a tachymeter depends on the required level of detail. This is used to measure the so-called Ground Control Points (GCP), i.e. the control points. The creation of these control points is necessary because the orientation of a measurement image is determined with them. Although measuring with a tachymeter is the most accurate method on the market, drone measurements provide other decisive advantages.
What is an RTK drone?
Real-Time Kinematics (RTK) is an advanced satellite positioning technique that uses a ground station with a known location as a secondary positional reference to provide more accurate data. When an RTK system is integrated into a drone, position data from virtual and physical base stations is combined and contrasted to correct the drone's camera location in real time. When deployed correctly, the drones can generate location data accurate to the centimeter, which is embedded in the aerial image during flight.
RTK requires two types of data connections during flight: one between the remote controller and the RTK base station and another between the remote controller and the drone. The connection between the controller and the base station is prone to unstable network connections, while the connection between the controller and the drone can be affected by obstacles near the launch point. To reduce the risk of losing data connections, PPK is an excellent alternative for surveying operations taking place in remote areas with poor signal reception and/or with obstacles such as trees, buildings or metal structures.
What is PPK?
To reduce the risk of losing data connections, PPK is an excellent alternative for surveying operations taking place in remote areas with poor signal reception and/or with obstacles such as trees, buildings or metal structures. With post-process kinematics (PPK), the data is corrected after the drone flight and not during the flight. The data is stored on board the drone and the calculations are generated on the computer after the drone flight. This allows for more flexibility and reliability. Even if real-time data connections are lost during the drone flight, the accuracy of the results can be maintained because the calculations include the PPK data. The location does not have to be perfect and the range from the base station can be extended.
It can be stated that both drones with RTK and PPK solutions provide data accurate to the centimeter:
RTK solutions require a base station and more specific circumstances in general for the launch and flight environments to be able to process real-time data.
PPK solutions offer more flexibility in how and where drones can be deployed for flight missions and greater reliability thanks to longer range.
2D drone survey in the orthophoto
Drone surveying in construction
Drone surveying is becoming increasingly important in all areas of the construction industry . The use of drones in the construction industry has skyrocketed in recent years for engineers as well as construction companies and drone service providers. The advantage here is that the drone can not only take pictures, but also carry out measurements based on the 3D modeling that was created by the photogrammetric recordings.
Building Information Modeling (BIM) is a visualization of the size, scale, and functionality of all systems in a building. A drone uses this computer-aided design and overlays realistic lifelike 3D models to ensure accurate construction to plan specifications.
From the start of a project, drone surveying is used in BIM for a permanent record of construction work, in addition to remote viewing and compliance verification. Not only is drone surveying a great way to ensure the completion and quality of work, it helps accurately throughout the construction cycle. When the project begins and surveys need to be taken, drone surveying is used to get accurate measurements and understand exactly where to lay the foundation and where the property lines end.
a constraction drone survey is also used to measure the amount of cut and fill to create a level foundation. Based on this, drone surveys can help create a realistic 3D model using photogrammetry software.
The benefits of drone surveying over rough terrain
Another advantage of drone surveying relates to the crucial advantage for the surveyor of no longer having to walk through rough terrain. This not only saves valuable time, it also increases security. Because in places that are difficult to access and generally in dangerous areas, there is an increased risk for the surveyor, who can fly over the areas with the drone from a safe distance. This increase in safety plays a major role in opencast mining in particular.