How to Decide Flight Altitude for Drone Mapping and Inspection?
Updated: Feb 20
In this short article, we will discuss how to decide flight altitude for drone mapping and inspection.
So what key factors are there to consider when deciding your flight altitude and why are they important?
The key to any drone operation is safety. As you will be using an automated software program, Hammer Missions, for example, it is always recommended to determine the height of the structure or building that you are planning on inspecting or mapping. This can be done very simply by using a few methods.
If it is safe to do so, and you are in the field ready to operate, you can fly your drone to the height of the structure and take the measurement from the drone's onboard altimeter. This can then be used in Hammer Missions to configure the correct altitude to perform the operation safely.
Use Google Earth Pro to calculate an elevation. This can then be used in Hammer Hub for pre-planning your intended mission. For further information on how to use Google Earth Pro to calculate the elevation of a structure or building please see this link. This method should be used in conjunction with a visual safety check when you are on-site and ready to perform your mission.
Rule of Thumb #1 So the first rule of thumb is that your flight altitude must be higher than the highest structure on site.
2. Regulations & Pre Flight Checks
It might sound like stating the obvious, but it's also important to check the altitude restrictions in your specific geography. What's the max altitude you can fly at and could you get permissions to fly higher?
Also, it's all very well pre-planning your mission, whether that be by using flight planning software or an automated platform like Hammer Missions but it is highly recommended to always perform some simple pre-flight safety checks before you take off. Check your environment for hazards and re-check the intended altitude of your mission to make sure you haven't miscalculated any of the heights. Above all, fly safe and keep your eyes on the aircraft.
Rule of Thumb #2 So the second rule of thumb is that your flight altitude must be lower than highest allowed altitude for your drones in your geography.
3. GSD (Ground Sampling Distance)
Ground Sampling Distance, as the name implies, refers to the amount of ground/surface area covered by a single image in flight. If you're flying a mapping flight with the camera facing down (nadir position), then this distance is basically the amount of ground covered by your drone per image in flight. If you're flying vertically and mapping a tower or a facade, then GSD is basically the amount of facade surface area covered by a single image in flight.
Depending on how big or the small the defect on the asset is (e.g. a crack on a roof or facade), if you are flying an inspection, we can expect to be able to see its resulting size in the images depending on the chosen GSD. For example, if the defect is only 100 cm in reality and we could go for a GSD of 10 cm/pixel, then the defect would be 10 pixels long, whereas if we go for a GSD of 1 cm/pixel, then the defect will be 100 pixels long. Depending on the size of the image, this would represent a fraction (%) of the image. For a 4000x3000 image, this would be ~2.5% of the image.
As you can see from above, GSD is frequently expressed as cm/pixel. As implied, this refers to the amount of ground or surface area covered by a drone image and will be affected by the altitude that you intend to fly at.
Rule of Thumb #3 So the third and final rule of thumb is that you want to aim for an altitude that is as high as possible which keeps the GSD as close to target as possible. If your GSD is too high, keep lowering the altitude.
Our post Calculating Ground Sampling Distance (GSD) in Drone Flights looks at this subject in further detail.
We hope this guide helps you plan your flight altitude for drone mapping and inspection. If you'd like to learn more about how to high-quality data safely and get the most out of your drone missions, please feel free to visit our learning resources.
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— The Hammer Team