Vertical reference for waterway navigation channels

Abstract From the Canadian patent

A method for measuring depths of a waterway (Fig 1) including the steps of , determining nautical chart vertical reference values along a selected waterway (Fig 2), building a data base of the reference values and storing the data base in a computer accessible from the vessel (Fig 2) providing a radio , receiver on board the vessel and Global Positioning System (GPS) equipment accessible from the vessel (Fig 2), and operating the computer radio , receiver, and GPS equipment to continuously obtain positions of the vessel horizontally (Fig 3), and computations as to depth of the vessel above a pertinent vertical reference value (Fig 4).