WHOI-90-52

The world of electronic chars divides itself into two categories: those that are intended to be
use as the legal equivalent of a paper char, and those that are an aid to navigation where the
conventional paper char meets the legal caage requirement.
This paper wil discuss both typs in order to describe the status and future development of this
emerging field of application in the martime electronics industr.
The Technology Qf Electronic Chars
Electronic Char systtms are derived from computer tehnology and in parcular from the
strengths and capabilties of the personal computer. An electronic char system involves the
following elements:
1. A stored replica of a nautica char in digita with varous features held in a set of fies
all related to the area covered by the digitized char. Thus, the loction and description
of buoys, lights and other aids to navigation are each kept in a separate file and caed
to the screen whenever the parcular feature is selecte for viewing. Some items, like
the coastlne, are generally always in view; others may be selecte at the user's option.
The sce of the display is selectable by the user, and it adheres closely to the sce of
the char of data from which it was create. If rada is employed, the sce of the char
wil match the sce of the radar image being added to the display.
The program that controls the on-board computer incorprates a scheme for the automatic
selection of the displayed char base upon the loction of the vessel. In this mode of
operation, the char in view always includes the current position of the vessel. In other
cases, the user ca select any area contaned in the computer's files to display other
places of interest.
2. A positioning system that loctes the vessel and which generates a symbol on the display
that represents ths position. This electronic system ca be Lora, the newer Global
Positioning System (GPS), one or more of the other satellte positioning systems, or a
Dead Reckoning estimate of position base upon an input of vessel spe and course.
3. An electronic display that combines char information with the vessel's position. Color
is generaly employed to distinguish shore from water areas and to display buoys and
lights in their actual colors. However, some of the lower cost systems may offer only
a monochrome display. .
The resolution of the display determines the degree of deta that ca be incorprated in
the electronic char.
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