Case study: drone surveying of a large industrial complex

Long Satisfying Weekend of Drone Surveying At BMW Mini Plant in Oxford.

At the end of September, Crucial Services spent a long weekend at the BMW Mini plant in Oxford. The project was to provide an overall photogrammetry survey of the whole site and several thermal surveys, all by drone. Drone surveys are quicker, safer and more cost-effective than a traditional land survey.

If you are interested in this sort of survey for your project or site, please get in touch, and we will be happy to assist.

Drone photogrammetry survey at BMW Mini in Oxford

The challenge

The survey was challenging, with many considerations to mitigate in the flight planning stage. Given the size of the site, several photogrammetry flights were needed. Maintaining VLOS (Visual line of sight) around the tall buildings and site infrastructure was a primary concern. As a result, extra hands were needed to assist with safety marshalling during flight operations. Over that weekend, the workforce was operating at lower staffing levels, which helped matters.

The weather was fine. However, the ideal conditions for a thermal mission differ from a photogrammetry mission. Ideal conditions for photogrammetry missions typically need overcast days. Thermal inspections of PV panels need predominantly sunny conditions with low wind and high sun. In contrast, thermal surveys looking for water penetration or thermal bridging must be carried out as temperatures shift from cold to warm. Fitting those into the schedule for multiple photogrammetry flights was tricky. We had to switch between mission types throughout both days to capitalise on the optimal conditions.

As part of the mitigations, we opted for the smallest drone possible that fulfilled the standards required by the client. In this case, the DJI Mavic 3 Enterprise was accompanied by a Mavic 3 Thermal drone. We could have used one larger drone with two different payloads, but that would have had a different risk profile not entirely suited to the job.

Our client was also surveying the site with mobile LiDAR, which took place on Sunday using the Trimble platform. They aimed to acquire a combined cloud from both data sources before extracting a topographical survey and other deliverables. Our client had previously established ground control across the site. See more about the importance of ground control points: Unlock the Benefits of Ground Control Points: What You Need to Know.

Drone Photogrammetry Flights

Aerial image of the Oxford BMW Mini plant

The video below shows a section of one flight from 13 separate flight missions. It shows the DJI M3E’s ‘Smart Oblique’ function and real-time terrain flowing in action.

In total, 35,000 images were taken on site over the whole weekend. To survey this site by traditional means would have taken considerably longer. Judging by the existing control station numbers visible on the ground, a traditional land survey would need several hundred control points. If each takes an hour to survey, you can soon start to do the maths to calculate how long it would have taken to survey this site by traditional means. This would be a month on site and involve several survey crews and a lot of other overheads, too.

Reality Capture: The results of the photogrammetry survey

After some substantial heavy lifting and processing days the results of the photogrammetry survey look impressive. Below is a video fly-through of the model:

Click here if you would like to have a deeper dive into the Reality Capture textured 3d model of the BMW mini plant (1.4Bn triangles simplified down to 197.8m triangles and 11.01 gigapixels).

Drone Thermal Surveys

Rooftop solar panel array during one of the thermal surveys at the BMW Mini plant in Oxford

The thermal missions were broken down into three categories: Roof Inspections, PV Inspections and plant inspections. Each mission type has its own considerations for the optimal collection of data:

• Roof Inspections – looking for water penetration problems. Water is slow to cool and warm. Surveying early in the morning and late in the evening are the best times. This minimises the sun’s influence on ambient temperatures and thermal load in the structure to be measured.
• Photovoltaic inspections – looking for faults and inefficiencies in solar panels. This is best done on a sunny day when the sun is high, with low wind, so that the panels are measured when they are under a high thermal load.
• Plant inspections – looking for heat loss, mechanical and electrical failures. These surveys should be carried out when the equipment is in use.

Learn more about thermal surveys with a drone

Have a site like this that needs a survey?

Managing this asset can be challenging if you have a large site like this. Lengthy surveys can be expensive. So, if you have a site like this one that needs a topographical survey or a thermal survey or routine surveying, then feel free to contact us to see how we can help.