Page 98 - Electronic Navigation Cyber Book

Electronic chart types
There are many different types of electronic charts available that use
different formats, different levels of content and attribution, and may, or
may not, be official charts. As described above, all presently available
electronic charts are either vector or raster. For the former, the chart may
be based on the IHO S-57 format or some other format. Only if the level
of content and attribution of the chart conforms to the IHO ENC product
specification and is produced by, or on the authority of, a government
authorized hydrographic office, can the chart be considered an ENC as
defined by the IMO ECDIS performance standards.

Electronic navigational charts (ENC)
These are the designated charts for the ECDIS system and they possess
a single universal data format.
Such charts use vector data based on the IHO Special Publication S-57,
edition 3, IHO Transfer Standard for Digital Hydrographic Data. Some of
the major points which identify the unique property of these charts are as
follows.
• They are issued by or on the authority of a government-authorized
hydrographic office.
• Items on the chart must be attribute-coded and must be able to be
interrogated to provide information.

Admiralty Raster Charts (ARCS)
ARCS/Seafarer charts are produced from the same process used to print
paper charts, i.e. a rasterized process is used either to print a paper chart
or produce a raster chart. They are accurate representations of the
original paper chart with every pixel referenced to a latitude and
longitude. Where applicable,
horizontal datum shifts are included with each chart to enable the chart,
and any information overlaid on it, to be referenced back to WGS-84. Not
all available charts have WGS-84 shift information and such charts must
be used with caution when a GPS position fix is applied.
UKHO ARCS and Australian Hydrographic Office (AHO) Seafarer both
produced in the UKHO’s proprietary hydrographic chart raster format
(HCRF). ARCS is updated weekly using a CD-ROM with the same
information as the weekly Notice to Mariners used to correct paper

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