Aerial photogrammetry has so many applications, especially when it comes to survey practices. However, it has traditionally been limited by expensive helicopter aerial imagery stitched together – but drones have changed all that! The affordability of aerial photogrammetry unmanned aerial vehicles (UAVs) have opened up the possibilities for many companies to use this new technology to great advantage… but what makes a good drone for photogrammetry?
Multi-rotor Versus Fixed Wing
The most fundamental choice to make is whether you require a multi-rotor or fixed wing drone design. Both have their merits and downfalls!
A multi-rotor is easier to fly, especially when it comes to take-off and landing, and provides a unique hover ability ideal for taking aerial images. Less pilot skill is needed, especially with GPS plotted flights, meaning photogrammetry surveys can be autonomous – ideal for a company new to using drones.
However, fixed wing aerofoil designs are the dominators when it comes to survey drones, and this is because the traditional design allows for far greater distances to be covered in one flight. While a multi-rotor can hover, large batteries are required for this and the payoff is a heavier battery and therefore reduced flight time. The glide possibilities of an aerofoil design of a fixed wing means significant power savings, and a lighter drone overall.
Fixed wing drones do take more practice to fly: while autonomous and semi-autonomous flights are possible with GPS, it’s advised that a pilot is able to take full control. This sounds simple enough, and with advanced telemetry systems on-board is fairly true – but the pilot’s spacial awareness still needs to be good! A fixed wing drone will ‘flip’ the controls when it turns to fly back towards you – so what was ‘forward’ on the control is now ‘backward’ etc – meaning great skill is required to avoid the dreaded crash!
Photogrammetry Camera Types
You’ll need to consider exactly the type of photogrammetry mapping your drone will be used for: some types of map will require more than a traditional visible spectrum (red, green, blue or RGB) camera.
A visible spectrum camera will provide high definition images of the landscape, with great levels of detail, but may miss topographical features especially when vegetation is dense.
Normalised Differentiation Vegetation Index (NVDI) cameras are able to provide very detailed images of vegetation – making them ideal for agriculture or environmental research. NVDI cameras operate by a ratio of near infra-red images minus red reflectivity, over NIR plus red reflectivity. The differentiation is what provides the levels monitored in images to deliver very detailed vegetation analysis.
Multispectrum cameras are the daddy of them all! A multispectrum camera uses visible (red, green, and blue or RGB) spectrum AND near infra-red together, making them perfect for incredibly detailed photogrammetry images. The biggest downside, as you can imagine, is that more features make for a larger price tag.
GPS Camera Tagging
Whatever camera you choose to use on your photogrammetry UAV, it’s ideal to ensure you can include GPS tagging on each image. This helps software stitch images together seamlessly, and also means repeat flights can be made with the exact same locations for images when surveys are required over time to monitor landscape elements.
And finally, think about how far you’re going to need to lug your drone! Often launched from middle-of-nowhere fields with little road access, it’s best to ensure your UAV can pack down into a reasonable sized case which you can carry with relative ease.
The weight of some photogrammetry UAVs can be off-putting, especially with larger multi-rotor drones, so it’s important to consider the carry case used is as light as possible while remaining rugged to withstand regular transportation. Luckily, fixed wing drones as usually used for aerial photogrammetry tend to be lighter thanks to the efficient aerofoil design, so the more rugged cases can be used without adding too much additional weight.