ANNEX 3
DRAFT SN CIRCULAR
DIFFERENCES BETWEEN RCDS AND ECDIS
1 The Maritime Safety Committee, at its seventieth session ( ........ 1998), adopted amendments to the performance standards for Electronic Chart Display and Information Systems (ECDIS) to include the use of Raster Chart Display Systems (RCDS).
2 These amendments permits 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 be only used with appropriate folio of up-to-date paper charts.
3 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 RNC data, itself, will not trigger automatic alarms (e.g. anti-grounding). However, some alarms can be generated by the RCDS from user-inserted information. 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. In some instances, this may appear as a shift in position. This difference may be most noticeable at grid intersections and during route monitoring;
.4 chart features cannot be simplified or removed to suit a particular navigational
circumstance or task at hand. This could affect the superimposition of radar/ARPA;
.5 without selecting different scale charts, the look-ahead capability may be somewhat limited. This may lead to some inconvenience when determining range and bearing or the identity of distant objects;
