Introduction
On a rainy and windy Saturday morning at 6:00 AM, the Technical Team – East (mostly), consisting of Clinton, Seii, Sophia, and myself (Aden), assembled at the University of New South Wales (UNSW) to conduct a survey and create a photogrammetry model of an exhaust stack and its adjacent walls. The aim of the project was to deliver a 3D model to enable engineers to perform an accurate assessment of the structure, a task that would have been expensive, time intensive and difficult using traditional methods like scaffolding or rope access. The drone survey and 3D model was our innovative solution to overcome these challenges.
Safety Measures
To minimise disruption and ensure pedestrian safety, we carried out the survey early on a weekend. Upon arrival, we established a drone exclusion zone and activated a NOTAM (Notice to Airmen) with CASA (Civil Aviation Safety Authority) based at Sydney Airport to notify ATC and other aircraft operators of our drone activity in the area.
Additional Requirements
To create a detailed 3D model, we captured images from various angles, including 15-degree obliques both upward and downward. For the top of the structure, we captured images at 30, 60, and 75-degree angles, as outlined in the attached site capture plan. In total approximately 1600 images were captured.
Equipment & Technology
Our equipment of choice was a DJI Matrice 300 drone, equipped with a 35mm camera. To achieve centimeter-level accuracy, we had DJI’s RTK (Real-Time Kinematic) to use but opted to use the local NTRIP (Networked Transport of RTCM via Internet Protocol) point located within the University for GPS positioning.
Survey Process
Before commencing the survey, Seii gave a site brief and Clinton imparted some of his years of knowledge to us. A reconnaissance flight was then conducted to familiarise ourselves with the area and identify any potential obstacles. Then, it was time to capture the data. We maintained an 8m distance from the structure, allowing us to achieve a 1mm level of accuracy for the photographs. The drone, moving at a speed of 0.5m/s, captured images every 2 seconds, with a distance of 4m between each photo, and a maximum height of 57m.
Survey Parameters | Values |
---|---|
Distance from structure | 8m |
Photo accuracy | 1mm |
Drone speed | 0.5m/s |
Photo capture interval | 2 seconds |
Distance between photos | 4m |
Challenges and Teamwork
Despite the challenging weather conditions, with very strong winds and frequent rain showers that forced us to pause the operation five times, we successfully completed the data capture, within our time window. Clinton, our primary drone pilot, brought extensive experience and expertise to the project, proving invaluable in navigating the complex environment and difficult conditions. Seii, the project lead and secondary drone pilot, oversaw the operation and provided additional flying skills. Sophia, who was present to gain valuable flying experience and understand how drone captures work in real-world situations, also flew the drone to assist in the capture process, marking her first flight out of training in especially demanding conditions.
It’s worth noting that while different sensors (ie drone, phone and other handheld cameras) can be used for such projects, it is not recommended to mix data from various sources, such as drones and handheld devices.
Data Processing and Deliverables
The data captured during this one-day survey will require approximately four days of processing before it can be delivered to the client. And for planning purposes, it is estimated that around 5km of linear assets can be captured in a single day using this drone capture method.
Conclusion
In conclusion, despite the challenging weather conditions and the complex environment at UNSW, our team successfully completed the drone survey of the exhaust stack and surrounding walls. The data collected will now undergo processing to create a detailed photogrammetry model to be delivered to the client, enabling their engineers to conduct a thorough assessment of the structure without the need for costly and time-consuming traditional access methods. This project showcases Technical-East’s teamwork and technical expertise in delivering high-quality results for our clients.
Contact Us
If you have any questions about drone survey services or would like to discuss a potential project, please don’t hesitate to contact me.
Aden Petersen