By Alexey Dobrovolskiy
With the rapid growth of the drone industry, the interest from construction, engineering, real estate, and insurance communities in using UAS for building, roof, and infrastructure inspections is observed globally. This can range from inspecting buildings, bridges, chimneys, open pit walls, dams to communications and electrical infrastructure like cell towers or wind turbines. Traditionally these types of inspections are performed by highly trained inspectors using rope or scaffolding, making them more dangerous and thus driving up the cost. Fully automated drone vertical inspections are not only safer, they also allow for more precise data collection, which is very important for post-processing.
Automating vertical inspections in North America
Many cities in the United States are mandating building facade inspection programs to proactively identify any unsafe conditions that could pose a risk of injury or damage to property. For example, in the city of Chicago, all buildings with a height of at least 80 feet need to be inspected every 4 to 12 years based on the category of the building. Noticeably, it is possible for stakeholders to perform these surveys using drones without getting a waiver from the Federal Aviation Administration (FAA). Moreover, with the nationwide deployment of Low Altitude Authorization and Notification Capability (LAANC) and the 14 CFR Part 107 by the FAA, it is now possible to obtain approval to perform drone inspections of these objects even when there are multiple airports or helipads around. (Barnhart, Marshall & Shappee, 2021)
In Canada, dam inspections with the use of a UAV are an extremely innovative area where there hasn’t been a lot of growth. For detailed crack mapping and inspections, the traditional method is to send teams of engineers out on the structure, sometimes using rope access, where they have a harness, and they climb down the structure and manually measure each crack and then map each of them out with pen and structural drawings. A UAV method of data collection is more efficient, much safer for the team, and creates a digital model that can then be referenced over time which is extremely important. For example, a Canadian trend setter in UAV-based dam inspections, Niricson, uses drones because the method allows them to capture high resolution imagery and build a 3D model of the structure that they can now reference for future inspections. The company, in particular, opted for vertical scanning with a UAV in a Colorado project. They wanted to make sure that they maintained a consistent ground sampling distance, or basically, a consistent pixel size for the images, and the approach allowed them to quantify those cracks. Furthermore, they managed this to be repeatable in future surveys to compare how the structure would be changing.
Advantages of performing automated vertical inspections compared to manual drone inspection flights
Performing vertical drone surveys over manual surveys could be considered advantageous thanks to higher accuracy, repeatability of flights, increased crew safety, and lower costs. The result of vertical scanning surveys with a UAV is a set of images captured with a specific forward and side overlap, which can then be stitched together into a vertical orthomosaic or even a 3D model. This information can then be used to detect defects such as cracks or other damage. For example, in case of building inspection, this can more accurately estimate facade renovation costs and, after the repairs are finished –to check the quality of work of contractors.
Performing these types of inspection flights manually would be a difficult task for even the most experienced UAV pilots. This is the reason why most professional surveyors are moving towards automating it with the use of a flight planning software. Since drone surveys are repeatable with a high degree of accuracy, a software may allow the creation of a digital model of the structure after each survey flight, giving the ability to compare multiple models over time to see how the structure is changing to, for example, monitor if any cracks are developing over time.
According to Mark Patrick Collins, Associate Professor, Unmanned Systems, from Indiana State University, UgCS, mission planning and flight control software by SPH Engineering, was confirmed to be applicable for building and roof inspections. UgCS allowed users of a focus group to create a façade flight plan vertically across each facade of the building to perform this type of inspection safely and accurately. Users could set the distances from the building and the overlap and UgCS automatically calculates the optimal flight path for the vertical grid pattern. (Barnhart, Marshall & Shappee, 2021)
Workflow of planning vertical inspections using drones
Performing vertical inspections with drones can be divided into three phases – flight planning, execution, and post-processing.
Flight planning is started by drawing polylines on the map around the object. Next, the distance to the object is measured in the software and entered in the parameters. Similarly, the type of camera used and overlap parameters are entered by the operator along with minimum and maximum altitude values. Two inspection directions can be selected – horizontal or vertical. Vertical is more efficient for taller objects while horizontal is better for longer buildings.
The main parameter used when calculating the flight lines is the distance to the facade. The more accurately the flight is planned using polylines and maintaining a constant distance to the facade, the more consistent the ground sampling distance (GSD) of the end result will be.
Next camera actions are added. This allows the camera to automatically trigger either by time (every X seconds) or by distance (every X meters). Camera attitude action is added as well, setting a desired angle.
In cases when the structure is located on an uneven terrain, it is necessary for the flight planning software to be able to plan the mission according to the terrain elevation model. For example, in the UgCS software by default SRTM4 elevation data is used and it is possible to plan flights at a constant AGL (above ground level) altitude. Moreover, when doing centimeter-level precision flights very near to the side of a building, custom terrain elevation models imported from LiDAR scans can be used.
For flight execution the planned route can be either executed from the desktop PC or downloaded offline on a mobile device or the drone’s smart controller so that the laptop does not need to be used in the field.
Useful tips / notes when performing vertical scans with drones
Firstly, it is important to remember that GPS signal quality may decrease when flying very close to a tall vertical building. Pilots should therefore always keep the drone RC in their hands and monitor the signal quality.
Secondly, in relation to the point above, it’s important to keep the drone in visual line of sight (VLOS). Since a flight planning software like UgCS allows to plan vertical scans where the drone goes around the corner of a building, the pilot should always follow the drone in these cases and not fly BVLOS. Alternatively, a visual observer, who is in direct communication with the pilot, may be used.
Alexey Dobrobolsky, Co-Founder and Chief Technical Officer at SPH Engineering– SPH Engineering is a multiproduct drone software company and UAV integration services provider. Founded in 2013 in Latvia (EU) as a UAV mission planning and flight control start-up, the company has evolved from a developer of a single flagman product UgCS to a market leader of multiple drone solutions. Today the company has created a rich global customer and reseller network in 150+ countries while over 45 percent of partners are located in North America. Alexey Dobrobolsky is Chief Technical Officer, Member of The Board and Co-Founder at SPH Engineering. He has introduced a number of solutions recognized by the global market like the software to manage drone shows and drone-based industrial product lines. As of today he is responsible for strategy management and development. He likes to work a lot in a field to test SPH solutions in real life scenarios.