Mining & nature resources发表时间：2023-04-07 17:55 Miners face major obstacles. From designing mine infrastructure to capturing detailed mine features, our enterprise solutions help you overcome challenges.
Low-cost UAS Photogrammetry for Mining Exploring Consumer-grade Copters for Quarry Mapping By Unmanned aerial survey (UAS) photogrammetry has proven to be a good alternative for capturing open-pit mines, but it is expensive when done professionally. This article investigates whether low-cost UAS photogrammetry, using consumer-grade copters, is sufficiently accurate for 2D and 3D mapping of quarries based on a project in Australia. The Yilgarn quarry, located in the Western Australia, produces just over a quarter of a million tonnes of crushed stone and gravel each year. The quarry covers over 70 hectares, of which 36 hectares are actively exploited today, and its depth reaches 50 metres. Surveying from the ground is not only cumbersome and tedious because of the large extent of the area, but also because many parts of the quarry are inaccessible. For example, accurate calculation of the extracted gravel volumes requires coordinates of sufficient points on steep slopes and ledges (Figure 1). Furthermore, since ongoing earthworks often destroy ground control points (GCPs) and targets, monthly checks and repairs of the geodetic reference system are required. Besides that, there are of course safety considerations; ledges are unstable, and the heavy machines make a lot of noise as they continuously move around, posing an accident risk.
Figure 1, Many parts of quarries are often difficult to access for land surveyors. Low-cost Copter Capturing the area from the air helps to resolve these problems if proper hardware and software is available. UAS photogrammetry has been applied all over the world for capturing open-pit mines. The quality and usefulness of the geodata obtained are affected by weather conditions, magnetism and other natural forces. While professional solutions are robust against the impact of extreme temperatures, gusts of wind and other environmental conditions, they are also pricey. This raises the question of whether consumer-grade copters equipped with cameras are able to deliver geodata products of sufficient quality. To answer this question, the authors carried out a case study using the low-cost DJI Phantom 3 Pro quadcopter, which can be purchased for around USD1,000 and is equipped with a 12MP camera with fixed focus. The latter is advantageous because it contributes to the stability of the interior orientation parameters of the camera. The copter can stay in the air for half an hour on one battery charge, which allows the coverage of a relatively large area in one flight. Using Pix4D or DroneDeploy software, a flight plan can be preprogrammed which allows images to be captured in automatic mode and eases the planning of the photogrammetric survey. Survey The authors planned to cover the area with two flights of 30 minutes each at a flying height of 120m to obtain a ground sampling distance (GSD) of 5cm and 80% along- and across-track overlap. However, at the time the survey was conducted, the temperature had dropped to below 15C° which was too cold for the battery to provide sufficient power. That problem could be solved by warming the batteries in advance, but then a second problem arose: a strong wind which blew over the quarry with a speed of over 10m/s. Once the UAS had reached the planned flying height of 120m it was caught by the wind. To avoid the UAS deviating too much from the preprogrammed path, the flying height was lowered to 60m where the wind was less strong. However, as wind affects power consumption, this halved the flight time from 30 to 15 minutes, thus increasing the number of flights necessary to cover the area from two to six. Nevertheless, it was possible to complete the survey within one workday (eight hours) with only two batteries. By the end of that day the copter had flown over 12km and covered 36ha, capturing 1,324 images with 90% overlap and a GSD of 3cm (Figure 2). Since GCPs were necessary to georeference the images and derived products in the local coordinate system used, 11 GCPs were placed at the edges of the quarry and their coordinates measured with a total station. Seven temporary GCPs were measured in the centre of the quarry aimed at computing accuracy statistics, also with a total station.
Figure 2, Flight paths of the UAS survey. Surveying & Engineering We support measurement professionals with premiere solutions in the surveying and engineering fields. |
