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Surveying Water Pipes

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Surveying water pipes

Commendium accepted the challenge of surveying an 800m long 0.9m wide water pipe in North London. Being underground, without the aid of location, provided by GNSS. Surveying a metal pipe poses one of the most challenging subjects for LiDAR. There are few clues in the scanned data to assist with the registering and alignment of scans.

The challenges

We set about overcoming the challenges by mounting a Riegl TLS scanner into a crawler remote vehicle (provided by The Water Services Group). The process was set up to take scans at every 3m through the length of the tunnel.

Inertial measurement unit

We supplemented the displacement measurement by using an IMU to measure orientation and displacement between scans as precisely as possible. Scans were taken manually by connecting the scanner via a fibre optical link. Using ethernet switching also allowed us to capture photographs and video at the same time.

Scan Processing

Back at the office, the scan data is realigned using data from the IMU (Inertial Measuring Unit) . Next step the scans were brought into RiScan Pro for manual, fine stitching using the MTA (Multiple time around) tools. It was vital to prevent roll, and pick tie points from small imperfections in the pipe, revealed by the scanners. There is no way around this slow manual process. However, the results of our labour were excellent, a tribute to the quality of the core Riegl LiDAR technology.

Closing the survey loop

We ‘closed the survey loop’ by surveying over the surface, to the opposite end of the pipe, this time enabling auto-registration as GNSS , with plenty of street ‘furniture’  available to identify and align the scan data. In the end, the loop closure was just under two metres over 1.8km; that will do nicely.

Pipe Anomalies found

The scan survey showed in detail, four additional anomalies that were unknown to the client engineers. Had these not been identified, it could have rendered planned maintenance ineffective. It did mean that additional access had to be dug to address issues, but this remains hugely less expensive and time-consuming than the alternative.

Commendium 3D LiDAR water pipe survey

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