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Surveying technical Processing UAV acquired data by Faith Beta and Ajay Harduth, RocketMine This article shows how RocketMine acquires data, the quality and accuracy of the data acquired, and how the data is processed into various formats suitable for different customer requirements. I n 2014 RocketMine Aerial Data Solutions (RocketMine) became one of the first companies licenced to operate and own remote pilot aircraft systems (RPAS) in South Africa. The company offers a comprehensive solution for aerial data acquisition, processing and dissemination. An integral part of RPAS photogrammetry is the actual data that is acquired from the surveys. Because data collection has been made simple using RPAS technology, energy is now focused on analysing and using the data collected. RocketMine works closely with the mining, agriculture, GIS, and urban planning industries. It is involved with sourcing the equipment and technology to deliver accurate data according to clients’ specifications. The industries they currently serve are the mining industry (coal, platinum and gold), quarries and telecommunications. Projects have also been completed in the agriculture and construction industries. Fig. 1: Area identified and surveyed by both GPS and an RPAS. This means different types of data is used differently by the various industries. The methodology RocketMine uses to acquire data is not the one-solution-fits-all kind. It is tailor-made to suit the clients’ environment and output expectations. Through years of experience and an expert team, the company knows what solution best fits which environment and industry. The equipment used for the acquisition of data is dependent on the type of data that is acquired, and the outcomes that are anticipated. Fixed wing RPAS are used mainly for surveying and large-scale aerial photography. The sensors used on the fixed wings are (but not limited to) red, green and blue (RGB) cameras and near-infrared spectroscopy (NIR). The multi-rotor RPAS is used mostly for inspection and small scale photography. The sensors in the multi-rotor are (but not limited to) thermal and RGB cameras and multispectral sensors. 28 Fig. 2: Data plot acquired by GPS measurements from surveyors. Generally, the data acquired by RPAS in the mining industry are used for calculating stockpile volumes, mapping steep, inaccessible inclines, compiling optimised blast designs, and managing pit and stockpile changes from a remote location, as well as monitoring surface stability safely. Data accuracy: A case study The following case study was conducted by a RocketMine client to compare and contrast the accuracy and the quality of data acquired by RPAS as opposed to the traditional method of GPS. Accuracy is particularly important in areas of difficult, complex, or loose terrain, busy roads, and areas where there may be undetonated explosives from blasting. The aim was to compare RPAS data to traditional terrestrial methods. After a coal mine was identified for the survey, PositionIT – April 2016 SURVEYING technical a blast profile was designated, and pre-marks were placed around the area of interest. Surveyors initially surveyed these points using GPS instruments, before RocketMine conducted an RPAS survey on the same blast area. The data from the two surveys were sent for analysis. Analysis What took the terrestrial surveyors hours to collect and process, took RocketMine 25% less time to collect and process. In the terrestrial survey the surveyors’ personal safety was of concern as they were walking among loose rocks and steep inclines, and as there was no guarantee that there were not undetonated explosives around the area. There was also a high wall the surveyors could not climb over or take readings from. In the end, the RPAS survey contained more detail than the GPS survey. The RPAS was able to take measurements from above the high wall, whereas the GPS was unable. After plotting the data from the RPAS measurement, the survey did not move from the designated area. Thus, in terms of geo-referencing, the aerial survey was accurate. The mapped data results are depicted in Fig. 2. After making the comparison, the client concluded: • RPASmeasurementsdonotundergo a geospatial (positioning) shift. • Duetolooserocksandbigboulders, certain areas could not be accessed by GPS surveyors walking a round the blast, but the RPAS was able to safely cover all areas. • Intermsofhumansafety,RPAS measurements eliminate the exposure of unsafe ground, loose rocks and other obstacles that may pose to surveyors who have to walk and take measurements. • UsingRPAS,ittakeslesstimefor data to be collected and eliminates the need for surveyors to spend many man-hours walking around the same area. • Dronemeasurementtakesinmore detail accurately, including but not limited to the areas below obstacles, such as high walls in this case. • Additionally,varioushigh-quality outputs can be generated from the information gathered by the RPAS, in this case the team got a PDF file image in 3D. Acquiring data for clients As soon as measurements are acquired by RocketMine, the data measured is processed centrally. Depending on the industry where it is needed, PositionIT – April 2016 Fig. 3: Data plot acquired by RPAS measurements. Fig. 4: A summary of the cross-sections from the surveyor’s measurements. it is presented in a format that is tailor-made for consumption by the unique user. RocketMine does an analysis of what the client wants and decides on the best methodology for processing of the data. They then give clients advice on the best type of RPAS data for their needs. For example, a client may need to track the movement of their equipment for purposes of accountability, and they are given a heads-up on how the project will be carried out from its inception to its completion. They are also told what type of data will be produced, and how long it will take. RocketMine offers clients solutions in two ways. First, with an A-Z approach in which RocketMine does everything for the client – from 29 SURVEYING technical supplying the RPAS, the operating personnel, acquiring the data, to processing the acquired data and then giving the client a finished product. Secondly, an integration solution, in which RocketMine offers a part of their services as an outsourced part of the client’s project. This means that they fit into the client’s team at the point of need. The client’s team determines where the company’s team comes in, what they should bring, and how their input should blend in with their existing project. Whatever the case may be, RocketMine has the capacity to start and finish projects in as little time as possible. They normally require very little input from the client. Depending on the information the client needs and gives, work can start and finished on the same day they meet with the client. Types of data acquired RPAS data is always acquired in the form of images. It is then imported into RocketMine’s specialised professional photogrammetry software for processing. Because image quality is important, image correction and enhancements are also performed so that the images produced are of the highest quality. The data is then transformed into any of the following types of products, depending on the client’s needs: • • • • 30 Point clouds: sets of data points in a 3D coordinate system that represent the external surface of a terrain or object. Orthomosaics/orthophotos/images: files containing aerial photographs geometrically corrected so that the scale is uniform. Digital elevation models (DEMs): files containing elevation values representing terrain height over a specific area of the Earth. It is a “bare earth” elevation model devoid of vegetation, buildings and other objects that are above Earth’s surface. Digital surface models (DSMs): files containing elevations that include buildings, vegetation, power lines and other above-ground objects. The ground is only seen when there is nothing else on it. • 3D PDF images: files with images that provide a depth perspective. • Video fly-throughs: videos showing movement of the camera through a predefined path. • Normalised difference vegetation index (NDVI): images containing remote sensing measurements Area/department Industrial application of data acquired Pit and dump management Short-term planning Communication of daily/weekly mining plans Haul route surface optimisation Storm damage assessment and control Haul road, dump and pit design Geotechnical Long-term planning Surface stability monitoring Joint mapping Control for mining in void areas Mapping of steep inaccessible inclines Up-to-date surfaces for optimised blast designs Drill and blast Pre- and post-blast data Identification of misfires and wall damage Geology Stock pile management Grade control and exploration planning Drainage and water management Hydrology Watershed, drainage basin and water flow mapping Thermal detection of ground water inflows Tailings dam management Feasibility studies Construction Leach pad, dam wall and platform construction quality control Progress monitoring and reporting Mineral exploration Resource calculation Geophysical and watershed/catchment area modelling Supporting photography Reporting Erosion detection Heritage and environmental management Vegetation change tracking Inundation tracking Slurry pipeline stability and leakage detection Game counting Surrounding community mapping Cadastre Property rights definition Legal Change detection Security Incident evidence capture Corridor and boundary surveillance Community relations/marketing Community Impact reporting Oblique imagery Table 1: The types of data RocketMine acquires for the mining industry. that assess whether the target being observed contains live green vegetation or not. These are normally used for rehabilitation areas. RocketMine specialises in point clouds, orthomosaics, and DSMs. Data processing The data acquired is accurate with a very narrow margin for error. Its accuracy means that it is generally delivered to the client within 24 hours of acquisition, since there is not much editing that needs to be done. Once the still images are collected by the RPAS, they are processed using specialised photogrammetry software. The process of optimising images for data purposes can be loosely translated in four steps. PositionIT – April 2016 SURVEYING technical Step 1: Exploration and mapping of data. The RPAS is assembled, prepared, and put out in the field for mapping. Step 2: Checking image quality. The quality of the images can be checked and adjusted even when the RPAS is still in the field. Step 3: Generating orthomosaics, 3D models and point clouds. Once the images have been downloaded, generating the desired output is an almost fully automated action. The operator can generate the desired output from the drone’s images. The photogrammetry software handles all the calibration and processing, and in a few clicks the operator has the desired output. Step 4: Assessing and editing images. This steps improves the quality of the images provided, and the user can add text and other objects directly into the software. The added objects will then be added to the final generated output. Fig. 5: A summary of the cross-sections from the RPAS measurements. Table 1 shows the types of data RocketMine acquires especially for the mining industry, and Table 2 shows the various types of data that RocketMine has previously acquired and has capacity to acquire for their clients in other industries. Other RPAS data uses Lost time injury (LTI): LTIs are injuries that occur at the workplace that result in an employee’s inability to work in a given time (loss of man hours). Instead of sending a surveyor to survey the extent of the damage or loss, a drone is deployed to safely and swiftly carry out the assessment. This is to avoid loose ground, undetonated explosives, and hilly terrain if a human being was to go to the same place. Investigations: When there has been vehicle accidents, a drone can be deployed to get a full view of the impact instead of having a human navigate the impact zone. This minimises the risk of injuries and possibly fires. Both these investigations use visual, using thermal and RGB sensors. Fig. 6: A closer look at the wall that the RPAS was able to measure. Industry Plant counting Canopy measurement Agriculture For more information about RocketMine, RPAS data outputs and other projects the company does, visit www.rocketmine.com. PositionIT – April 2016 Vegetation index calculation Livestock detection Plant health reports Stockpile evaluation GIS Volume calculation Production and works Monitoring Disaster monitoring Conclusion Data acquired by RPAS has the ability to increase productivity and capacity since the tasks traditionally done by many people over a long period of time can now be done in a short time space with minimum personnel. Industrial application of data acquired Urban planning Stockpile calculations Work and progress Monitoring mapping Table 2: The types of data RocketMine acquires for other industries. References [1] Drones for Mining: www.sensefly.com/ applications/mining.html Contact Ajay Harduth, RocketMine, Tel 086 112-3738, [email protected] 31