Cansel’s Peter Afshar creates customized solution for the Canadian Hydrographic Service

True North | Spring 2018

Along the QEW highway connecting Toronto to Niagara Falls, not that far from city of Hamilton and just beside the “Skyway”- a huge suspended bridge- is where Canadian Hydrographic services (CHS) is located. 

The Canadian Hydrographic Service (CHS) is part of Fisheries and Oceans Canada and is responsible for nautical data collection and processing into paper and electronic nautical charts, hydrospatial services, Tides & Currents Tables and related databases.

Among various data collection tools in their arsenal, CHS relies on specialized boats and vessels mounted with different state-of-the-art sensors such as GNSS receivers, scanners, sonars, navigational aids such inertial measurement units, to name a few.

Proper integration of the data collected is of dire importance, hence requires a rigorous calibration and precise measurements to determine the relative position and orientation of sensors to each other. 

Traditionally, conventional land surveying techniques have been used for this task with hit-and-miss results. These methods are known to be infamously painstaking, elaborate and tedious.

In an exceptionally warm February morning in 2016, the Cansel Scanning team was escorted to one of these “super vessels”, hanging on a sling boat beside the quarry: CHS Harlequin (Ottawa).

Thanks to mild weather, mild wind and tolerable temperature, no operational constraints were observed. With little prior experience utilizing 3D laser scanning techniques, the CHS team took a very careful approach to this project. FARO Focus X330 was the perfect tool for the job due to its specification: 2 mm accuracy with wifi capability. Being light and small proved to be very important as in at least 2 scan positions the scanner could be mounted on a 5 meter high tripod and could be controlled remotely by wifi connectivity.

Like any other survey with high-demand accuracy, “redundancy” was reckoned to be of vital significance. The scan positions were selected for higher than normal overlap and more spheres and checkerboards targets were used to satisfy redundancies and checks.

It is common in a 3D laser scanning project to strategize on the registration technique beforehand, be it survey based, target based or cloud based registration methods. Registration is a term used for calculating the right position and orientation of each scan relative to a reference scan. The Cansel team decided to adopt a target based technique as the optimal method using cloud based as back up and verification, very unique to Faro workflow. 10 scans with different resolutions were performed with between 1-3 mm spacing on the surface of the vessel.

Two of the scan positions turned out to be very tricky. The first needed to be put under the boat to scan the sonar sensors and the other inside the cabin to scan the IMU. Registration results were excellent with 1.1 and 3.0 mm for target based registration and cloud based respectively. Of course the purpose of scanning was not just the integrated registered point cloud. Now it was time to extract information!!

Thanks to Faro Scene software, further processing was followed flawlessly. According the CHS requirements, the pointcloud needed to be integrated into a “special coordinate system”, such that Z direction is heading toward down and positive direction of Y axis would point to starboard. 

Faro Scene features such as plane creation and alignment control were used to define such a coordinate systems and all the required measurements were successfully extracted from the project: 

1. Offset distance of the two GNSS antenna from the IMU center

2. Height of IMU and GNSS antenna from transmitter Sonar, etc.

Another demanding part of the project was to measure/calculate the inclination of the transmitter and receiver relative to each other and the defined XYZ axis of the vessel. Again through Faro Scene it was possible to extract the coordinates to the planes on the transmitter and receiver by applying linear algebra. Done! Our angles were calculated!

The results were passed to CHS authority. When the ice thawed in arctic, the Harlequin was lunched for a new nautical voyage and the managing software was loaded with the parameters from 3D scanning. All parameters passed with flying colours. 

Upon successful completion of this project, Cansel was commissioned three more times (twice in Ontario and once in Nova Scotia) to apply this customized technique to new vessels. Results were confirmed once again after deployment of the vessels into water.

The detailed procedure of this project will be presented at an upcoming nautical symposium: “2018 Joint Canadian Hydrographic and National Surveyors’ Conference”. It is almost certain that this will become a standard routine in sensor calibration in CHS.