Skeye was asked by our sister company Deep BV from Amsterdam to participate in a project to create a 3D model of a breakwater in Georgia. The breakwater was damaged as a result of a collision with a vessel that sank in front of the breakwater as a result. The breakwater was surveyed below the water by a team from Deep using a dual multibeam echo sounder. Above water Skeye carried out the aerial survey using the Altura Zenith ATX8 drone equipped with a 24-megapixel camera. The images were collected using a pre programmed flight path so as to ensure sufficient overlap between the images.
The flights were conducted at a height of 40 meters above the breakwater and in total around 300 images were taken in seven different flights.
In addition to images straight down a large number of oblique photographs were also taken to eliminate shadow areas. For each image its position, heading and orientation were also logged.
To obtain the required accuracies around 40 ground control points were marked on the breakwater and measured using RTK GPS.
The data was processed using a combination of different software packages. In a first step all the images were aligned and tied together using recognisable points in the overlap between the images. In average around 40,000 points per image were found as tie points. In a second step the 3D point cloud was further Densified to a total average of more than 1500 points per m2. Each of these points represents a height (Z), a location (X,Y) and the colour from the photographs (R,G,B). This 3D point cloud was then used to create a 3D digital terrain model (DTM) with a cell size of 5 cm.
As a last step an orthophoto mosaic was created. This is one seamless photograph made from all the individual images whereby corrections are applied for colour differences and terrain heights. The result is a photograph to scale on which direct measurements are possible in a CAD or GIS package.
Deep integrated their underwater 3D model together with the 3D Digital Terrain Model by Skeye to form one integrated model.
The quality control showed that an average height deviation of a mere 3mm was obtained with a standard deviation of 18 mm.