DJI Mavic Pro flying on its autonomous mission.

Well, what is an aerial survey? In fact, what do any of these terms mean? Aerial survey, aerial photography, aerial mapping, photogrammetry? The list, so it seems, is endless. Quite understandably, to those outside of the industry, these various terms may be quite confusing.

Here, we have tried to briefly explain what each of these terms mean.

Aerial surveys

By an aerial survey, we refer to a process of collating data from an airborne craft. The purpose of a survey is to record an “as is” state or to better understand a specific subject. All of our aerial surveys are currently carried out with a drone. Drones are small and efficient and can easily access many places.

Collected data can take many forms – it really depends upon which sensors are added to the craft. Cameras, which are essentially visual sensors, capture photos or film. They also record data about the capture itself. Focal length, aperture and speed of exposure are just a few of those. Thermal imaging sensors record thermal signature of objects and living things. GPS records the position of the craft. And so on. You get the picture, right?

However, the survey does not quite end there. Gathering data, or data acquisition as we call it, is only one part of it. After the data has been collected, it needs to be processed and converted into a desired format. This could take form of a 3D topography mesh, a land survey drawing, an orthomosaic photo, and so on.

Common examples of drone survey include land surveys, visual inspections and thermal inspection surveys.

The video below, shows a 3D mesh generated from one of our aerial surveys. It was developed from around 900 geo-tagged images captured from air. The survey allowed an engineer to develop his structural concepts and provided invaluable information later during construction.

Aerial Photography

Often during an aerial survey, we would take many photos. Still, aerial photography is not a survey. The difference is in the final use. Whilst a survey is carried out to record or to understand, the purpose of photography is the photo itself. Does that make sense?

The photo is taken to be pleasing, artful, to express a feeling or to show off a feature. The purpose of a commercial image is to sell a product or a lifestyle, or to explain an idea or a concept.

One could argue that photos also serve as a record. And yes, they do. So are they not a survey? To continue down this path would lead to a philosophical debate, which we leave for some other time and place. Agreed?

Aerial Mapping

Essentially, aerial mapping is a process of collection of ground data from air and conversion of data into a spatially accurate map. All photos taken during a flight are collated and aligned. Stereo-photogrammetry is used to derive 3D position of points on the photos. And finally, an orthomosaic map is created. In essence, an image with uniform scale and free of perspective distortions. An orthophoto. Such an image can then be used to measure true distances or sizes of objects on the ground. Great!

Orthomosaic map of old city walls by the river Danube. Aerial Mapping: Map generated with a ground sampling resolution of 3.5cm/px.
Aerial Mapping: Orthomosaic map generated with a ground sampling resolution of 3.5cm/px.

To view more orthomosaic images, visit our aerial mapping gallery.

Photogrammetry

The Wikipedia defines it as a “science of making measurements from photographs… for recovering the exact positions of surface points.”

In our case, we mostly mean stereo-photogrammetry, where common points are identified on two or more photos. A number of photos with a common point are then assessed. Lines of sight from the camera to the common point are triangulated. And 3D coordinates of the point are derived.