A Croatian-based land surveying office, Grmoljez Stjepan, was commissioned by the Dubrovnik municipal waste management authority to provide a detailed topographic survey of a waste treatment site.
Waste disposal infrastructure needs to be regularly monitored for quality assurance and land movement detection. This surveying office, specializing in open-pit mines, quarries and construction sites, proposed drone-based mapping and photogrammetric processing to meet the requirements at a fraction of a cost.
The site contains a main landfill area, access roads, and a few smaller pits to the sides, serving mainly as alternatives for potential expansion.
A rotary drone was chosen for the task as the surveyed area was small and fairly close to the road. SkyHero 8 along with a compatible flight control system seemed perfect for the task. A flight at 100m paired with Olympus EPL7 was conducted for a total flight time of 10 minutes. GPS was used to determine GCPs (ground control points) prior to the flight itself for improved precision and orientation. The size and shape of the site allowed for an image overlap of 60% horizontally and 70% vertically to ensure accurate processing and 3D modelling.
Image processing was done using the 3Dsurvey software. GPS data from GCPs positioned on site was used to orientate the model to generate a dense 3D point cloud from aerial images.
The flight was conducted in winter and the low sun caused shadows within the landfill area itself. Upon analysis of the data, the shadows did not cause 3Dsurvey software any problems, and the resolution and quality of the results have far exceeded the client’s requirements.
The following results were provided: A digital surface model (DSM), a digital terrain model (DTM) by removing the above-ground obstructions such as trees and bush, a georeferenced orthophoto in realistic colours, a height map to graphically indicate the level of waste in the fill itself, contour lines, profiles, and a detailed survey map. All this was achieved by utilizing 3Dsurvey alone. There was no need for exporting to GIS or CAD as all the tools and features are fully integrated within 3Dsurvey software.
Advantage of This New Technology
Drone photogrammetry produces LiDAR quality analysis results at a fraction of the cost associated with LiDAR. Analysis of the results provide extremely accurate cut and fill volumes, land mass movement detection by comparing measurements over time, hi-res models for detailed post-flight inspection, and a fully customizable and measurable 2D and 3D outputs.
Project Tools & Specs
Drone: SkyHero 8 (10-minute flight required for this project, general max flying time on a single battery is 25 minutes)
Camera: Olympus EPL7
Positioning & Orientation: GPS used to place GCPs (ground control points)
Photogrammetric processing & Outputs: 3Dsurvey software
Number of Images: 475