Hull Modeling Using Point Cloud Data from a Handheld LIDAR

Capturing 3D point-cloud data of a large, irregular shape is not easy. In the case of a ships hull, it can be quite tricky, indeed. Add to that the complex environment of a busy dry-dock, with construction and rigging equipment strewn about , achieving a closed surface mesh by scanning with a terrestrial LIDAR is near impossible, if not at least expensive and time-consuming.

The folks at QNTFI Ltd. in New Zealand (a start-up firm focused on quantity surveying) have found a novel solution to speed data collection while maintaining quality and surface coverage. They use a handheld device called the Zeb1, sold by 3D Laser Mapping. (LiDAR News previously reported on the Zeb1 in a product review back in February.) Recently, QNTFI was contracted to scan a commercial fishing ship that had undergone structural alterations.

The marine vessel that was scanned had been retro-fitted with a 1.5 meter extension to the hull. This modification required that analysis of the load capacity of the vessels hull be conducted before being approved for return to service. In New Zealand, as in many countries with regulated marine vessels, hull design and modifications must be approved for stability and structural integrity among other factors. With the advent of laser scanning, creating a high-fidelity engineering model of a hull has been made faster and easier to do. Consequently, this allows marine engineers to more rapidly asses a vessels compliance with the appropriate marine regulations and thus minimize down-time following modifications.

In the case of QNTFIs project, using a static terrestrial scanner would not have been economically feasible, principally due to the array of equipment and personnel distributed around the ship. The objects and people obscured clear lines-of-sight to the hull. Using a tripod mounted scanner would have necessitated multiple set-ups and would have required registration of the scans. Using the handheld LIDAR allowed QNTFI to work around obstacles as well as access the underside of the hull, which was perched on blocks.

In an odd way, the various tooling, platforms, rigging and construction materials scattered adjacent to the ship actually presented an advantage to the Zeb1. The handheld scanners simultaneous localization and mapping (SLAM) algorithms perform more effectively when there are non-uniform environments in the field of view of the LIDAR. While the clutter presents obscuration difficulties to a tripod scanner, and would require multiple set-ups and/or clearing away the working area, the QNTFI operators were able to walk between the objects and hull, thus optimizing lines-of-sight to the hull surface as they waved the scanner head. Maintenance and some painting were able to continue unimpeded by the scanning process.

The LIDAR data was ported to a CAD program where a marine surveyor from Emtech Engineering & Marine Consultants created hull lines (fine resolution profiles of just the vessels hull area). The hull lines and meshed surface were then used to create a water-tight model in CAD. Finally, complex hydrodynamic analyses (including fluid flow and structural calculations) were performed on the 3D model of the vessels hull. The analysis can include subjecting the model to virtual forces generated by different wave profiles emanating from calm to storm-like sea conditions.

According to Martin Haanen, Managing Director of QNTFI, the marine engineers evaluate (in a virtual mode) a wide array of situations, from normal operating to emergency. These analyses take into account load capacities in different locations on the vessel including fuel and catch [weight], according to Haanen. Using the 3D model, the engineers even go so far as to simulate scenarios for impaired performance due to damage or loss of functionality.

QNTFI staff were on site for a little over an hour, according to Martin Haanen. They conducted two separate scans, each time completely walking around, and on, the 48 (14.74m) vessel. Haanen stated that they wanted to ensure coverage, so they performed the second scan to act as a back-up. Each scan took only 15minutes to complete.

Haanen commented that the fishing vessel needed to be returned to service as fast as possible since the window for meeting the catch quota was closing. The ability of QNTFI to quickly get the point-cloud data to the engineers at Emtech was a critical aspect of the project. Using the Zeb1 to access hard to reach areas and avoid multiple set-ups, targets and scan-to-scan registration made for a rapid turnaround on the project. Even though the little hand-held LIDAR produces only a 43 kHz pulse frequency, it is sometimes better to have a few points where you want them, than lots of points where you dont need them.

About the Author

Bill Gutelius

Bill Gutelius is the President and co-founder of Active Imaging Systems (AIS). In 2007 he formed AIS where he consults for commercial and government clients on active and passive imaging technologies and their applications. Previously, he spent more than ten years at Optech Incorporated where he enjoyed being actively involved in the emergence and development of world-class commercial LIDAR remote sensing tools now commonly deployed throughout industry and government.