Mapping drones – how do you deliver the best possible image
Sony’s head of sales for Russia, Middle East and Africa, Gary Quinn, talks to Geoscan’s Vladislav Vasiliev about the imaging requirements of its new Gemini drone, which is able to capture 150 hectares in a single flight and deliver resolutions down to 3cm per pixel[АГ1] (altitude 141m - or at 1cm per pixel at 47m) – see figure 1.
The conversation follows updates to Sony’s full-frame and APS-C camera SDK, which allows virtually any facet of the camera to be automated, and allowing Sony ISS’s business customers to benefit from the sensitivity, resolution and lens portfolio of Sony’s professional camera range – without losing the automation functionality.
The Gemini is a small quadcopter used for archaeological or mining surveys, for civil engineering projects and for geo mapping, including 3D maps. It embeds the Sony UMC-R10C and has a flight time of 40 minutes, with the flight path.
Fig 1: GSD, or the size of the real world captured by a pixel in a digital image, is based on the flight altitude and camera parameters
Vladislav Vasiliev: On a still day, and flying at a constant altitude of 141m, this 40 minutes allows us to cover up to 30 km, capturing approximately 150 hectares of land with a resolution of 3cm per pixel.
Image quality is vital for when undertaking surveys as it allows, for example, an archaeologist or an engineer to understand more easily and precisely where they need to spend time on.
Gary Quinn: So, when it comes to selecting the camera, what are the key criteria?
VV: Drones are used for so many different applications that there is no one perfect camera for all applications. But essentially, you’re balancing flight time with image quality.
This means weight is obviously a key consideration for every component on the drone, be it the housing, the battery, the GNSS system or the camera. Quite simply, every gram counts as the longer you stay in the air, the greater the area you can capture.
Fig 2: GeoScan’s routing algorithm visualization tool
Obviously, it’s not just as simple as making it as lightweight (or as aerodynamic) as possible. If a component lets you do more, even if it is heavier then that component will be selected. A good example of this is a heavier battery will give a longer flight time. And the camera is another good example: a camera with a larger resolution enables you fly higher and capture a wider area per frame. This means the returning flight paths can be much wider and the overall flight path will be much shorter despite still covering the same area.
For example, the 20 megapixel camera onboard the Gemini, flown at an altitude of 141m will capture 150 hectares (1.5 million square metres) and still have a resolution of 3cm per pixel.
However, image quality is also vital and merely selecting a camera or sensor with a larger resolution isn’t enough. The amount of light per pixel that the sensor lets is (the sensitivity) needs to be as high as possible and so we found that for our drone an APS-C camera delivered the right balance between weight /flight time, ground captured and image quality. This gives us less noise and a higher dynamic range, even in lower light conditions: allowing us to extend the day and worry less about cloud cover.
Fig 3: The size of a sensor impacts the quality of images, especially those taken from a lower altitude and at high speeds. By increasing the size of the sensor, the resolution (number of pixels) can be increased without shrinking pixel size and, therefore, the sensitivity (the amount of light reaching each pixel). By switching from a 1” to an APS-C or full-frame sensor, you can improve the ground sample distance to capture more accurate information and /or cover a greater area per image.
GQ: Indeed. We typically see drones with one of three sensor sizes: 1”, APS-C and full-frame. With full-frame sensor will typically be found in a camera like the Alpha (ILCE) range of professional cameras and has a sensor area of 860mm2, an APS-C sensor is 330mm2, and 1” is 116mm2.
Each application will vary in terms of what is needed. An inspection drone, for example, might use the full-frame cameras to deliver as high-quality image as possible. And an indoor drone might use a 1” sensor to cut down on weight and reduce the risk of damage to equipment if it crashed. Is that a fair summary?
VV: Yes. Our indoor drone, the Geoscan Pioneer, is designed to be as lightweight as possible and as such we’ve reduced the resolution to 8 megapixels. And at the other end, our Geoscan Lite fixed-wing drone embeds an Alpha [ILCE] 6000.
GQ: That leads me on to the next question… Drones have changed virtually every facet of filming and there is now such a wide range of use cases. As you’ve said, there is no one-size fits all and we’ve talked about the importance of the sensor, but what else do you see as the next key consideration in developing a drone, perhaps something you see people get wrong when designing drones?
VV: For us, a mistake is to not think about control. Even on our $185 educational drone (the Pioneer mini) we’ve built in the ability to run a fully autonomous flight path. The Gemini, for example, coupled with the Geoscan planner uses PPK/PPP methods holds its path with a 1.5 cm accuracy of projection centres coordinates, even with long baselines.
For example as well as GNSS positioning, we also use a radio link that allows us to keep the drone under control up to 5km away and a routing algorithm that doesn’t rely on a magnetic compass.
GQ: I’d back that completely, we’re seeing automation of every facet of the drone becoming a key criterion and as such the cameras themselves are also starting to enable a far greater range of functions to be software-controlled, enabling the adjustment of the dynamic range, the white balance, the focus via an SDK. This means image settings can be adjusted automatically mid-flight according to the changing weather conditions, or remotely from the drone’s control software.
For more information on the Gemini and Geoscan’s other drones contact email@example.com
For more information on working with Sony contact Gary Quinn (firstname.lastname@example.org).