A Brisbane based engineering firm contacted us on behalf of an interstate mining company to produce a high resolution contour survey of a small mining lease not far from Gladstone. While we do have experience producing high definition maps for vegetation assessment, weed monitoring and general site modelling, the word ‘survey’ is not for novices and meant we had to get the professionals involved. A call was made to collaborate with Sean from Robinson Engineering Surveys.
The first step as with any job involving drones is to complete a feasibility study to ensure the job could be completed safely. We also wanted to ensure we could deliver the results to exceed the clients expectations. A mapping mission was planned to cover the 10 hectare site, this included inputs from ground control points and traditional survey pickups. Sean uses a very high tech Global Navigation Satellite System (GNSS), Post-Process Kinematic (PPK) direct geopositioning system for drones. The GPS co-ordinates normally received by consumer drones can often be accurate within a few meters, with the addition of ground control points in mapping software, this accuracy can increase to several inches. Direct geopositioning dramatically improves the horizontal and vertical accuracy of drone mapping projects to a couple of centimetres or even millimetres.
When we arrived onsite we were greeted by a couple of friendly locals.
A few hours were spent taking reading around the site and setting up ground control points. The GNSS base station was set up for reference and the drone and PPK system were engergised to begin locking onto sufficient satellites. The automated drone flight was initiated using a pre-calculated mission on the mapping application. 278 nadir images of the site were collected over approximately 20 hectares.
Mapping software uses algorithms that enable the generation of high density 3D point clouds from the collected images with a high degree of overlap (60% to 80%). When using these techniques in aerial mapping, an orthographically corrected mosaic image is also typically created.
Creating such a model requires a very powerful computer. Trees and bushes also need to be removed manually to allow a clear view of the ground. Exports were created in specific formats required by the client and uploaded for immediate access.
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