16
.2 radar data representation on an electronic chart, elimination of
discrepancy between the radar image and the electronic chart;
.3 possible projection discrepancies between an electronic and paper
chart;
.4 possible scale discrepancies (overscaling and underscaling) in
displaying an electronic chart and its original scale;
.5 effects of using different reference systems for positioning;
.6 effects of using different horizontal and vertical datums;
.7 effects of the motion of the ship in a seaway;
.8 ECDIS limitations in raster chart display mode;
.9 potential errors in the display of:
.9.1 the own ship’s position;
.9.2 radar data and ARPA and AIS information;
.9.3 different geodetic coordinate systems; and
.10 verification of the results of manual or automatic data correction:
.10.1 comparison of chart data and radar picture; and
.10.2 checking the own ship’s position by using the other
independent position-fixing systems.
51. False interpretation of the data and proper action taken to avoid errors of
interpretation should be explained. The implications of the following should be
emphasized:
.1 ignoring overscaling of the display;
.2 uncritical acceptance of the own ship’s position;
.3 confusion of display mode;
.4 confusion of chart scale;
.5 confusion of reference systems;
.6 different modes of presentation;
.7 different modes of vector stabilization;
.8 differences between true north and gyro north (radar);
.9 using the same data reference system;
