How DJI’s L1 Makes Right of Way Surveys Flexible and Practical

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How DJI’s L1 Makes Right of Way Surveys Flexible and Practical

Right of Way (ROW) Surveys are tricky but incredibly important to Power & Utilities companies looking to expand their power grid. Especially in areas with dense vegetation and tree growth, in these areas, photogrammetry cannot provide bare ground level elevations. Without a reliable DTM (Digital Terrain Model), the next set of substations and power lines cannot begin. This is where LiDAR comes in. Using drone-powered LiDAR, we were able to survey the modest stretch of land quickly, efficiently and cost-effectively.

Photogrammetry cannot effectively obtain ground-level data in forested areas; this is because the thick canopy and understory block LOS (Line of Sight) to the ground. However, the lasers from the LiDAR scanner can pierce through the layers of vegetation to find their mark on the ground and return accurate data. Nevertheless, even in the case of non-forest areas, it may still be challenging to procure accurate data. This is because non-forest regions tend to contain more soil, shadow and shrubbery- characteristically, these features can be similar to trees and pose a challenge. LiDAR can accurately detect the ground level unfazed by conflicting characteristics.

Traditionally, if you wanted to capture LiDAR data, your only option would be to rent a manned aeroplane and an appropriate LiDAR scanner. Unfortunately, these LiDAR scanners are incredibly expensive, costing upwards of 180,000 USD- that's a considerable investment to bear. If you wanted to survey large corridors of land, manned-aeroplane LiDAR scans would be the way to go- giving you the ability to cover the area efficiently. But, what if you wanted to survey more modest parcels of land, like a 5 km corridor? 

Building Powerlines Across Mountains

In the capital of Turkey, a Power and Utility provider wanted to expand their network and construct powerlines going across a mountain in Ankara. The length of the survey corridor was a modest 5 km, but the terrain is the real challenge. First, roads were sporadic across the range, forcing the team to move on foot at points. In addition, the varied elevations posed a serious challenge to data integrity and drone safety. And finally, moving from one control point to another would take up a major chunk of the time, forcing the team to circle the mountain. Still, without a drone-powered LiDAR survey, this survey would have been incredibly expensive. 

Suppose you wanted to conduct this survey using the traditional method via a crewed aeroplane. In that case, these are the concerns you would have to factor in. First is the price of the LiDAR scanner itself- they cost upwards of 200,000 and in the region aren't readily available for rental. Second, hiring out a plane itself is expensive. Third, the closest airport from the survey site is located 200 kilometres away; this makes the total plane trip a sizable commute- further increasing the survey's price. Finally, the difference between the highest and lowest point is massive; the peak measures 1,200 meters and the trough at 400 meters in elevation. To maintain data accuracy and integrity, it is necessary to maintain a uniform altitude while taking measurements. This would force the plane to make dangerous manoeuvres to keep the height consistent. 

For the reasons listed above, manned plane surveys would be inefficient and impractical to map this stretch of land. On the other hand, Drones can fill in this gap of smaller-scale surveys, but until the advent of the L1, we lacked a feasible and effective LiDAR payload. This payload improves the drone's surveying capabilities, allowing it to provide precise data when photogrammetry cannot. In addition, the 3-axis stabilized gimbal provides higher density point clouds with 1 cm precision in True Color. The resulting dense point cloud makes it ideal for high-precision analysis and mapping elements like powerlines, vegetation indexing, contour mapping and encroachment inspections and powerline sag detection. Finally, the L1's inbuilt IMU further increases accuracy by working in tandem with the IMU and RTK onboard the DJI M300 RTK.

With the DJI Zenmuse L1 in tow, the team set out to survey the corridor. The remote and difficult terrain posed challenges for the team. Due to the varying elevations, the drone had to fly higher or lower to keep the data accurate. This puts the drone in danger and can even cause a situation where the drone loses connection with the operator. Secondly, the problematic terrain slowed down the team significantly, forcing them to take large detours and requiring them to move base stations often to maintain line-of-sight with the drone.

The challenging LiDAR drone survey was made considerably easier by DJI's Zenmuse L1 and M300 RTK. The L1's true colour live point cloud feature was instrumental during this survey. As the drone-captured data, the data was displayed as a true colour point cloud in real-time to the team. Using this, they were able to make mission-critical decisions in the field. It allowed them to rescan problem areas immediately to ensure the data captured was accurate and actionable. The L1's triple return mode- where three laser pulses target the exact spot helped assure that the reading we received back was from the bare ground level. Finally, this being a mountain made the surrounding climate volatile- resulting in high winds and rainfall. However, this wasn't a problem for the L1, rated IP54 ingress protection; the L1 could brave the weather and continue collecting data.

Using the L1 in conjunction with the M300 RTK, the team was able to survey the entire corridor in just 12 flights or just six hours. Then, using DJI Terra, they were able to process the collected data in record time. Generating dense and accurate point clouds from the collected data took just 30 minutes. Additionally, you could do it from the field itself. Given that you have a network connection- the DJI Terra processes the collected data on the cloud, allowing you to process on the go.

The DJI L1 allows us to collect LiDAR data at an extremely low cost, reducing the cost from 200,000 USD to $10,000 USD. Of course, if you were looking to conduct LiDAR surveys of large areas, a manned plane may be better suited. Still, for smaller to medium stretches like 5km corridors, the L1 allows you to get the exact data at a more flexible and accessible price range. If you'd like to see how you can benefit from the L1, get in touch with us- we'd be happy to set up a cost-free demo just for you.


About the author

Niiveth Mani


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