Electronic Charting System
In marine navigation, an Electronic Charting System (ECS) is the generic term, of the International Maritime Organization (IMO) and International Hydrographic Organization, for a device that, at a minimum, links a display, computer-readable charts and a Global Navigation Satellite System such as GPS. If the charts that it uses are certified by IMO or an IMO-approved organizattion, it is a legal replacement for paper navigational course charts used for ships and boats under international safety regulations. An approved combination of ECS and charts is called an Electronic Chart Display and Information System (ECDIS).
A more consumer-oriented term is chartplotter, which may be a function that runs on a commercial personal computer or a dedicated computer. Chartplotter tends to imply that the device will accept real-time electronic messages from devices beyond the GNSS, such as the vessel's autopilot, radar, sonar, automatic identification system, digital selective calling (DSC)-equipped radio, etc. The most common standard for electrical and message-level interfaces among these devices is NMEA 0183, from the National Marine Electronics Association.
If the NMEA 0400 installation standard is followed, the computer is dedicated to the purpose and may be modified only by approved technicians. Nevertheless, it is quite common, in recreational and commercial fishing vessels, to use a general-purpose computer. With due regard that the chartplotter is a safety-critical system, it may run other applications such as vessel monitoring system and catch reporting for fishing vessels, engine maintenance records, weather software, etc.
ECS may use one or both of two types of chart, raster and vector.
- Raster charts: precisely scanned images of paper charts, the accuracy of which depends on the map projection in use (e.g., conic or Mercator projections) and the navigational grid reference system (e.g., NAD-27 or WGS-84)
- Vector charts: contains data by which software generates a machine-processable chart and external display. Machine-processing allows, for example, the computation of distance between coordinates, and the superimposition of data from other navigational devices.
Vector charts are much more powerful, as they allow the software to be aware of the navigational environment, such as measuring the vessel's distance to shallow water or another vessel tracked in real-time, and giving warnings of potential grounding or collision.