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Electronic charts are shown on a screen: this may be part of a chart plotters or a dedicated navigational computer. The main ideas behind electronic charts connected to a position source is to relieve the Navigator of much routine work connected to paper chart navigation, and make possible the introduction of alarms. Ideally these improvements should enhance situational awareness.
The electronic map in the navigation system is more than just a map on the screenTypes of electronic charts
here are two types of electronic chart, distinguished by their production process: raster and vector charts. TjuvholmsElectronic charts are further classified as official or unofficial, depending on the manufacturer. Raster charts are scanned copies of existing paper charts. When displayed on a screen raster electronic charts have a strong resemblance to the appearance of paper charts.
The vectorisation of nautical information is a labourintensive procedure, as a result of which raster charts still cover a larger area of the oceans at the time of writing. This is especially true of regions with less traffic. However, vectorised charts are capable of incorporating a number of interesting functions, so the tendency is for vector-chartsto cover more and more of the world.
A chart contains information that the cartographer has chosen on the basis of the intended use. Rasterised charts contain the same amount of information as the equivalent paper chart, sometimes supplemented with additional information in a second data layer. Vectorised charts can contain much more information.
The main differences between paper- and electronic charts:
After a change in the SOLAS regulations the chart requirements can be met by official electronic charts in an ECDIS installation, as long as there is either another, independant, certified ECDIS or up-to-date paper charts as back-up.
Lines and areas on a raster chart are built up from pixels. On zooming, all details are enlargedlines broaden, etc.