Sperry Marine VISIONMASTER FT ECDIS-E, User Manual

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ECDIS-E User Guide Appendix B – Chart Datum Codes
65934012 B-7
YYY
IRL & OGB. These codes are used where a chart has been
compiled by fitting information on more than one datum directly to
the chart graticule without making adjustments for the shift between
the datums. They indicate that, at the scale of the chart, such
differences are not plottable, and the chart may be regarded as
being on either datum.
UND
Undetermined Code. UND is used where it cannot be stated with
any degree of certainty that positions read from the chart can be
related to any one horizontal datum. Where it is possible to
separately identify the datums to which different parts of the chart
are referred, then the chart will be subdivided for geographic
referencing purposes. In practice, there are large parts of the world
where insufficient data exists to relate a chart to any specific
horizontal datum.