What is the difference between a raster chart and an ENC?
Many CHS charts are available in digital form in either raster (BSB) or Electronic Navigational Chart (ENC) format. Both kinds of electronic charts relieve the navigator of paper-chart routines, and both are remarkable contributions to safer navigation.
Raster charts are simply an electronic image of the paper charts, and, as such, provide no more information than that available on the paper chart. Raster charts are digitized by scanning the paper chart. Each tiny segment of each line on a chart is converted to a raster picture element or pixel. These pixels are similar to a television picture or magnified newsprint in that they appear as dots on a grid. Beyond geo-referencing, there is no intelligence inherent in the image. Many recreational boaters have adopted raster electronic charting systems because the charts are less expensive, and the navigation software required for these charts has been tailored to meet the needs of the recreational boater.
Electronic Navigational Charts (ENCs) are vector charts or "smart charts" and carry additional information not available in paper or raster charts. ENCs carry a wealth of geo-spatial intelligence within the data and have a database of information associated with them. On an ENC chart, you can click on different features, such as a light or buoy, and retrieve additional information. For example, a wharf appears only as an image on a raster chart, but an ENC can identify it as a wharf and attach attributes to the wharf, such as height, length, age, ownership, number of berths and facilities – data that might otherwise be available only by consulting the relevant printed Sailing Directions.
ENC charts also allow users more control over the display of the chart, such as the ability to turn different layers of information on and off. Because ENCs offer more powerful navigational flexibility and tools, they are used by many commercial ships. When combined with GPS, radar, ship course, speed and draft in an Electronic Chart Display and Information System (ECDIS), ENCs become part of a powerful system that allows mariners to know their ship’s position instantly and accurately and to be warned of dangerous situations.
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