A survey was commissioned by a major port authority in the UK for a fuelling jetty used by a global oil major. The organisation wanted to have a direct comparison between traditional hydrographic survey techniques and drone-based survey, to ascertain whether this can be met by drones for their future needs.
The survey site was not a straightforward one, because the security and safety standards of the site meant even getting access to conduct the survey was a complicated process. Prior to visiting the site, a full risk assessment had been successfully submitted.
Upon arrival on site, extensive ID checks were carried out before a safety briefing. It’s elements like this that any commercial drone pilot needs to take into account when planning a project: the ID and safety checks took more than two hours to complete. If not adequately factored in the survey window may turn out to be too short to accommodate.
Assessing The Site
The fueling jetty which was being surveyed was 275m long. Two separate take-off points had been chosen prior to visiting the site, including one next to the jetty. However, there were challenges with this. The first was caused by the sheer amount of metal structures on the site. In fact, on-site were some of the largest cranes in the world – quite literally. In the photo below, our surveyors are close on 1km away from these cranes!
Cranes usually operate on a radio control system that is on 2.4GHz, the same as the drone. Our team used a spectrum analyser to confirm the potential levels of interference. Our pilot placed the drone on the ground at the furthest distance away from the ground control station (GCS) that it would be operating from the take off point allowing them to confirm the maximum safe distance they could operate the drone in flight. A test flight was conducted to verify this which identified a new challenge: the 5.8GHz band was very congested on the dock site. This caused potential interference at around 200m from the GCS and flight planning had to be amended to operate within these constraints.
One final consideration when conducting the survey was that the site was still in operation and our surveyors were required to work around existing operations rather than have a shut-down area to work from.
Common challenges included things like a take-off site for the drone being on a private road which was intermittently being accessed by lorries. For the safety of the surveyors and to ensure site operations were not interrupted, the survey was paused while the road was in use.
These challenges demonstrate the need to consider all contingencies when planning a survey for a site versus real-world conditions. Environmental factors can’t always be planned for!
Completing the NADIR (“camera flat down”) photography was completed successfully, with the ALTURA ZENITH AX8 flying a pre-programmed survey route. The oblique photography, which would provide greater detail on the vertical edges, was completed using the ground station computer to confirm the aircraft location and calculated field of view.
How The Survey Was Done
The aim of this project was to compare traditional surveys (done by survey boat and ground laser technology) with aerial drone surveys using photogrammetry. Through utilising this technology survey times are slashed and this type of survey is revolutionised.
UTILISATION OF PHOTOGRAMMETRY – PIX4D
Photogrammetry is the composition of multiple photos referenced against GPS positions to build accurate 3D models and maps. Inaccuracies introduced by the GPS on the drone can be compensated for by using ground control points. These are fixed points on the ground that are marked and located using a high precision GPS. You can see in the picture below a marked white square – that’s one of the fixed ground points:
Multiple photos are taken of the site, which are mapped together by overlaying the edges of each photo. To get the top layer, the drone flies straight and level above the jetty with the camera positioned facing directly down. To enhance the verticals of the jetty they needed to be photographed, too. This requires the drone to fly alongside with the camera set at a 45 degree angle.
Data Capture: The Results
Even with the challenges placed in front of us, the survey was a success. Check out the video below!
This model was created with the “flat down” images only.
A 3D model was constructed from the drone images that were georeferenced by the drone and calibrated with the ground control points.
As can be seen from this case study, photogrammetry on this venture was not plain sailing. Even once the images were loaded into the software, a problem appeared! Water can not provide match points in PIX4D– it changes all the time! This is why, on the model, there is some additional ‘noise’ around the jetty. Additionally the flights were taken at different times during the day, due to operational constraints, that meant that the water was at different levels with the incoming tide.
Lessons Learned From Jetty Survey
There were some interesting – but not unusual – challenges faced by the survey team for this project. Site expectations versus real-time environmental issues was by far the largest problem. Working against an operational site – causing interference and ‘blind flying’ – tested the skills of the team.
However, by being able to reference the field of view and operating distance, as well as knowing the exact camera angle required for the vertical data capture, a full and accurate 3D model was created. Even with the noise caused by the water an accurate model was delivered of the structural elements of the jetty.
The accuracy levels in the data compared to traditional survey techniques were sufficient for the drone to be considered for use in certain situations, in addition the fore shore model was very accurate.
Water is not your friend in this situation! It is also worth noting that sky is not your friend with photogrammetry either, so building models of vertical structures requires some careful consideration!
Steve Coulson, Founder of Coptrz, said of the survey: “As a former hydrographic surveyor and the also an owner of a commercial maritime company, I’m delighted that this demonstrates the capabilities of UAVs into different sectors when a project is planned properly and the correct hardware and software are selected for the job in hand. We hope to do many more projects like this.”
The software used to develop the 3D models is Pix4D – and Coptrz have just become the only company in the UK to provide approved Pix4D workshops and are an accredited partner and reseller of the software! Find out more by visiting the web page here.