Aerial Photography as applied to mapping was started in earnest by the military In WW1 and by WW2 was routinely carried out by the belligerents on all sides. My father, Sqdn Leader Peter Morris undertook many photo reconnaissance sorties. One such was in August 1943 over northern France in preparation for the Normandy D-Day landings.
A vast experience was accrued and in the peace that followed aerial photography blossomed and major technological advances were achieved. Aerial cartography for civilian purposes had become a global growth industry used for urban and infrastructure planning, agriculture and archaeology. However, it was expensive and very time consuming in the non-digital era and was invariably undertaken by costly manned fixed wing and rotary aircraft. This then heralded the satellite epoch, still a very costly method of photo data acquisition. But technological change has brought new opportunities.
The increasing use of UAVs (Unmanned Aerial Vehicles) for Photogrammetry and Lidar mapping in aerial surveys is not surprising. Using GPS enabled UAVs for aerial surveying is very cost effective in comparison to hiring an aircraft with costly specialist photogrammetry equipment and operators.
With GPS-equipped drones, digital cameras and powerful computers, surveys with an accuracy down to 1 to 2 cm is very possible.
The use of quadcopters and multirotors in photogrammetry and Lidar mapping is still in the very early stages but new possibilities are opening very rapidly.
What Exactly is UAV Photogrammetry?
Photogrammetry is the science of making measurements from photographs. The output of photogrammetry is typically a map, a drawing of a 3D model of some real-world object or land mass.
3D Maps and Models
To create 3D mapping from aerial photogrammetry, the camera is mounted on the drone and is usually pointed vertically towards the ground. Using photogrammetry to create 3D models of monuments for statues, the camera is mounted horizontally on the UAV.
Multiple overlapping photos (80 to 90% overlap) of the ground or model are taken as the UAV flies along an autonomous programmed flight path represented by a sequence of waypoints in the air. To overlap photos of an object or land by 80 to 90% would be impossible to complete accurately by pilot navigation. It is essential to have a UAV which has Waypoint Navigation technology.
UAV Lidar Mapping Explained
UAV Lidar (Light Detection and Ranging) involves mounting a laser scanner on a UAV to measure the height of points in the landscape below the UAV.
Fixed wing UAVs with Lidar scanners can capture hundreds for square kilometres in a single day. By measuring 10-80 points per square metre, a very detailed digital model of a landscape can be created. The accuracy of the measurements allows the 3D models created to be used in any planning, design and decision making processes across many sectors.
Lidar sensors can also pierce dense canopy and vegetation, making it possible to capture bare earth structures that satellites can not see, as well as ground cover in enough detail to allow vegetation categorisation and change monitoring.
At present, Lidar scanners have not yet been developed for rotary UAV’s but will be in the future given the pace of technological development.