Control point, RTK and ground station. What do you really need?

Almost every surveyor is familiar with the use of totalisers, control points and their clipboard. When surveying with drones, the question often arises as to whether an RTK ground station that communicates with the drone is useful or necessary. When do you need this feature and is the result accurate?

The applications in drone surveying are diverse, as are the requirements for the results. In order to select the right technology, it should be clear in advance what characteristics the result should have. Basically, a distinction must be made between three possible outcomes that can be the result of drone surveying:

1. Virtual 3D model that reflects the shape and structure of the object.

2. Virtual 3D model that reproduces the shape and structure of the object and is also dimensionally accurate.

3. Virtual 3D model that reproduces the shape and structure of the object and is dimensionally accurate and georeferenced.

In the first case, no ground station is required. The images from the drone are sufficient to create a 3D model. Frequent applications for this are digital twins in the form of 3D models.

In the second case, the ground station is helpful. By precisely determining the camera position and real-time communication between the drone and the ground station (using RTK), the 3D model later becomes dimensionally accurate. This means that distances, areas and volumes can be determined more accurately.

In the third case, the ground station is optional, but control points are mandatory in this variant. If both the ground station and control points are used, accuracy is increased. In addition, fewer control points are required and the calculation of the 3D model is significantly faster.

The term "virtual 3D model" is a generic term at this point. It can refer to digital terrain models, surface models, point clouds or meshing of the recorded objects.

Alternative to the ground station

You don't want additional hardware for your flights? No problem, as an alternative, correction data can be received in real time via the mobile phone network. The connection is established via a SIM card, which is inserted into the remote control on selected drone models. The GPS correction data can then be transmitted and the 3D model is later dimensionally accurate (case two). If you have neither a ground station nor a SIM card, you can still use your 3D model for surveying purposes. This requires reference dimensions that must be assigned in the model - also known as scaling.

Please note: Mobile radio is not available everywhere, which can be an argument in favour of the ground station.

When is georeferencing necessary?

Referencing the model is necessary if it is also to be in the correct position in the "world coordinate system" (case three). If, for example, several surveying services come together in a project, they should all be harmonised with each other, for example using an identical coordinate system.

If it does not matter where the model is located in the world within the world - for example, because only length, area or volume are of interest - georeferencing can be disregarded (case two).

Conclusion

Depending on the requirements for the result, the choice of the right equipment is crucial. We have tested a lot of hardware and software in the field of surveying in recent years. Take a look at our industry solutions and let us advise you individually.