UNIT 15

1. Read and translate the following text

TREATMENT OF HORIZONTAL DATUMS BY ELECTRONIC CHARTING SYSTEMS (ECS) / ECDIS

There are many different makes and types of ECS/ECDIS equipment and thus the following information is intended as general guidance only. Users need to consult their system manuals in conjunction with these notes.

Most electronic charting systems process and display positions using WGS 84 Datum for the horizontal reference, largely because they have been designed to work with GPS receivers as the primary positioning source. In systems that allow other settings, WGS 84 Datum is normally the default. As stated earlier, a significant proportion of paper charts and thus their digital equivalents are not yet accurately related to WGS 84 Datum. This obliges the ECS/ECDIS to be able to identify when position source and chart are working on different datums and take action either to make appropriate adjustments or provide a warning to the user.

Admiralty Raster Charts (ARCS)

ARCS charts (facsimile copies of the Admiralty paper chart) contain the same position shift information as that shown on the paper chart. Where a shift to WGS 84 Datum is available, the ARCS chart carries this information. This enables the ECS/ECDIS to automatically make the appropriate adjustment to allow the ship's position from GPS to be correctly displayed on the ARCS chart. Where the shift to WGS 84 Datum is unknown, this is explicitly recorded in the ARCS chart data and the ECS/ECDIS should display a warning that the plotted position is liable to be inaccurate.

<== попередня сторінка	\|	наступна сторінка ==>
Regional Horizontal Datums (1930s to 1950s)	\|	Other Electronic Chart Data

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