23-1
23. Radar Overlay
23.1 Introduction
The optional radar overlay has the radar echo image overlaid on the ECDIS chart display. The radar overlay video
can be received by ECDIS two ways:
• Via a radar overlay card fitted in the ECDIS
• Via LAN from FAR-2x07 radars
This ECDIS has many features to support exact match in scale and orientation of the chart and radar echo image.
Exact match of the radar echo image and chart is an essential security feature. If the radar echo image and the chart
display match, then the mariner can rely on what he sees and the mariner also gets a very good confirmation that his
navigation sensors (such as gyro and position receivers) operate properly and accurately. However, if the mariner is
unable to achieve exact match, it is a very strong indication that something is wrong and he should not rely on what
he sees.
This ECDIS can use radar echo image in several operator selectable modes. The "ECDIS only" mode operates
without the radar echo image. The "ECDIS and radar" mode operates using the rules for the type-approved ECDIS
to visualize the radar echo image. The "radar over chart" mode draws the radar echo image on top of the chart. This
mode should only be used temporarily because legally the equipment is not an ECDIS that can legally replace paper
chart when operating with "Radar over chart". The "radar video only" mode should only be used temporarily to
check radar echo presentation, because the equipment is not an ECDIS that can legally replace paper chart when
operating with the "radar video only" mode.
Selected scale of displayed chart also defines scale of radar overlay. When you change the chart scale, the scale of
the radar overlay is automatically changed. The maximum range of the radar overlay is 24 nautical miles.
The rule of thumb for range of displayed area:
• Chart scale 1:10,000 is almost equal to traditional radar range of 0.75 NM
• Chart scale 1:20,000 is almost equal to traditional radar range of 1.50 NM
23.2 How to Activate Radar Overlay on the ECDIS
The radar overlay can be output to the ECDIS and shown on its display. Like details on vector charts, the radar
overlay can be displayed or removed from the chart display You can select how to display the radar overlay with the
Radar selector on the status bar. To activate the radar overlay, put the cursor on the mode selector (location circled
below), spin the scrollwheel to select "ECDIS and Radar", "Radar over Chart" or "Radar video only" in the status
bar then push the left mouse button.
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