Contracting Governments undertake to co-ordinate their activities to the greatest possible degree in order to ensure that hydrographic and nautical information is made available on a world-wide scale as timely, reliably, and unambiguously as possible.
These amendments permit ECDIS equipment to operate in two modes: .1 the ECDIS mode when ENC data is used; and .2 the RCDS mode when ENC data is not available.
However, the RCDS mode does not have the full functionality of ECDIS, and can only be used together with an appropriate portfolio of up-to-date paper charts.
A raster chart is basically just a visual scan of a paper chart.
It is a computer-based system which uses charts issued by, or under the authority of, a national hydrographic office, together with automatic continuous electronic positioning, to provide an integrated navigational tool. Each point on the chart is digitally mapped, allowing the information to be used in a more sophisticated way, such as clicking on a feature (for example, a lighthouse) to get all the details of that feature displayed.
In 1983, IMO adopted a Resolution referring to the importance of the provision of accurate and up-to-date hydrographic information to safety of navigation and to the fact that many areas had not been surveyed to modern standards.
The Resolution invited Governments to conduct hydrographic surveys and co-operate with other Governments where necessary.There may also be differences in colours used during day and nighttime;.10 an RNC should be displayed at the scale of the paper chart.Excessive zooming in or zooming out can seriously degrade RCDS capability, for example, by degrading the legibility of the chart image; and .11 mariners should be aware that in confined waters, the accuracy of chart data (i.e., paper charts, ENC or RNC data) may be less than that of the position-fixing system in use. ECDIS provides an indication in the ENC which allows a determination of the quality of the data. Member Governments are requested to bring this information to the attention of the relevant authorities and all seafarers for guidance and action, as appropriate.The mariners' attention is therefore drawn to the following limitations of the RCDS mode: .1 unlike ECDIS where there are no chart boundaries, RCDS is a chart-based system similar to a portfolio of paper charts;.2 Raster navigational chart (RNC) data, itself, will not trigger automatic alarms (e.g. However, some alarms can be generated by the RCDS from user? These can include:- clearing lines - ship safety contour lines - isolated dangers - danger areas .3 horizontal datums and chart projections may differ between RNCs.Mariners should understand how the chart horizontal datum relates to the datum of the position fixing system.The amendments to the ECDIS performance standards indicate which performance standards for vector charts apply equally to raster charts, and add specific specifications for raster charts, covering such aspects as display requirements, alarms and indicators, provision and updating of chart information and route planning.