Ecdis And Datum; Ecdis And User Selectable Local Datum - Furuno FEA-2107-BB Operator's Manual

24. Datum
24.5

ECDIS and Datum

The real ECDIS uses ENC material, produced to standards using WGS-84 datum. Positioning devices connected to
the ECDIS must work in the WGS-84 datum. IMO requires that the ECDIS must give an alarm if the datum of a
positioning device is not the WGS-84. In practice this is impossible, because the standard used by positioning
devices (IEC 61162, previously NMEA 0183) does not include a datum message. Consequently, the classification
societies only approve a positioning device interfaced with the ECDIS in which datum cannot be changed (i.e., is
always WGS-84).
Note: The ability to check datum of position is a relatively new feature for position receivers. It was introduced in
standard IEC 61162-1 Ed2, published in July 2000. Only an EPFS (for example GPS or DGPS) which has "IEC
61162-1 Ed 2 (2000-7)" indicated in its type approval certificate can support the ECDIS to detect datum mismatch.
24.6

ECDIS and User Selectable Local Datum

The ECDIS allows the operator to change viewed datum. This selection of the datum does not change anything
inside the ECDIS for navigation calculation processes or for electronic sea chart display processes. But it changes
the numerical values of positions displayed on the ECDIS display into the operator-chosen datum. This is very
useful, especially if you like to plot positions from the ECDIS on a traditional paper chart.
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