New Zealand-based surveying, planning and engineering firm The Surveying Company created an impressive model of detailing a long stretch of coastal cliffs in the Hawke’s Bay region of the country’s northern island.
The scan covers 9.5km of coastline. It incorporates sandy shorelines, steep cliffs up to 140m high and jagged peaks.
The Surveying Company was contacted by engineering services firm Stantec on behalf of the local Hastings District Council as part of a risk assessment following a landslide in early 2019 that injured two Korean tourists who were subsequently forced into the sea. The beach was closed following the event.
What began as a mapping of the hazard area quickly expanded into scans of a huge section of coastline to provide a holistic risk assessment to the concerned local council and New Zealand Department of Conservation.
The huge 3D model was to serve as a baseline for future risk monitoring, the organisations involved took the view that having a complete model of the area would inform on areas of the beach would be safe to reopen for future access.
The Surveying Company used a DJI Matrice 200 drone equipped with an X4s camera to photograph the region, which proved difficult as the key area of focus was only accessible by 4WD at low tides. This gave the team only a three-hour window to collect data on each visit.
Prior to each flight, The Surveying Company established checkpoints and made temporary, non-toxic control markings which were measured using Leica GS16/GS18 RTK GPS to help accurately track photo position and match the eventual geography of the 3D model to the real terrain.
The team documented the beach in 1km sections via manual, pre-planned flights. Photographic data was later downloaded, assigned its relevant coordinate data and processed with Pix4d.
Once satisfied with the quality and accuracy of the data they had obtained, The Surveying Company generated points clouds, with some measuring in the vicinity of 25 million points for each kilometre of beach.
Some nine projects were then merged to produce the final model. In total, 155km of flights produced more than 12,500 photos. The survey team reports that their systems spent four weeks stitching the model together. The Surveying Company reported 3D accuracy of the project under 22mm and that average GSD / resolution for the entire job was approximately 2.38cm/pixel.
Check out The Survey Companies’ writeup for a more comprehensive overview at this link: https://www.surveying.net.nz/services/aerial-mapping/mapping-clifton-beach/
A video of the final model: