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Navigation Sensors · 347
Position alignment by means of the ARPA radar
User chart, showing coast line, buoys, etc., can be used as a position reference once the ARPA radar is able to see
these objects. If the ARPA radar targets and the User Chart are not exactly overlapping there is either position error
or gyro error or some combination of these errors. Some selected ARPA radar modes which can display User Charts
can perform position alignment.
ARPA radar without CHART ALIGN push-button
1. User chart must be available on the ARPA radar. (ARPA radar must be connected to the ECDIS and STORED
VIDEO MAP pushbutton of the ARPA radar must be pressed). Press Sensors button and select Position sheet
open.
Press Start button to
alignment with radar.
2. On the ARPA radar screen, locate a clear reference radar echoes and suitable User Chart lines or symbols.
3. Press Start button in Position sheet. If there was no User Chart lines on the ARPA radar display, then system is
unable to continue and generate alarm "2072 ChartAlign: No line avail". If there was User Chart lines on the
ARPA radar the system can continue and as a reminder of the ongoing process it generate and maintain alarm
"2061 Chart Align: Executing" during the whole process.
4. Use the track ball of the ARPA radar and move the User Chart so that it overlaps radar echoes.
Press Stop button when you
have defined alignment.
5. Press Stop button in Position sheet. The alarm "2061 Chart Align: Executing" disappears automatically and
the amount of alignment is transferred to the ECDIS and range and bearing of it is display in this field. If you
want to cancel the alignment process then press Cancel button and the process is terminated without any new
alignment.
6. If the position source is Dead Reckoning, then the system sets a new start position to the Dead Reckoning. In
this case there is no offset and no indication text OFFSET. If the position source is something else than Dead
Reckoning, then the indication of OFFSET is displayed on Upper information area. See Figure below.
Upper information area on ECDIS screen.