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Tuesday, February 9, 2016

Integrating Radar with Coastal Explorer

Back when I was defining V2.0 of the electronics for my boat, I made the decision to forgo a key feature - Radar Overlay.  Radar overlay is a feature that displays the radar return "overlaid" on your chart plotter so you see both the chart and radar return together on the same screen.  In my early years using radar I ran in this mode 100% of the time, and considered it a mandatory feature for any navigation system.  But over the years I have done a complete 180 on that view and now run exclusively with radar and charts in separate windows.  As a result, I was very comfortable forgoing that feature in my new electronics system, and instead opted for Coastal Explorer as my Charting program, and a couple of Furuno dedicated radars.

So what happened and why the change?

I think it all has to do with me practicing and learning over the years how to read a radar return, getting comfortable with it, and being able to quickly correlate what's on the radar screen with what I see outside the boat and on the chart.

In my early years using radar I really liked overlay.  Having the radar returns on the chart placed everything in context, and made it clear when a radar return was a rock pile or buoy as opposed to a boat.  This made reading the radar much easier.

The down side was that the radar returns sometimes obscured what was on the chart.  For example, the radar blip would make it impossible to see what the number was supposed to be on a particular buoy.  The reverse was a problem too.  Lots of info on the chart like soundings, contour lines, and bottom composition sometimes obscured a small radar blip and caused be to miss things or not see them as soon as I might have otherwise.  But these downsides were worth tolerating to have the radar return in context on the chart.

The screen shot below illustrates this.  On the left is a chart with radar overlay, and you can clearly see how the pink radar return correlates with the coast line and channel buoys.  It's a great training aid for practicing and learning how to read a radar return.  But you can also see how it becomes harder to pick out the boats and other moving targets on that screen given everything else that is presented.  And it's harder to see the details on some of the buoys on the chart because of the radar returns.  When you look at that chart, do you readily see all the boats that are around you?

In contrast, now look at the right had side which is a radar-only display.  To an unpracticed operator, it might be a bit harder to correlate what you see with the chart, especially if they are at different scales, but you have to also admit that everything stands out very clearly.  Just look at all those boats around you that you probably didn't see in the left hand overlay view.

What I have found over the past year or two is that I now always use separate chart and radar windows.  And I attribute it to having become more comfortable and fluent at reading the radar returns, and not wanting to miss anything on them.

With all the marine electronics vendors, the radar data format is proprietary, and only their chart plotters can overlay their radars.  There are a few cases of products that have reverse engineered very basic radar display like in OpenCPM, but I don't think any of them provide full functionality including things like ARPA.  It's basically a way for electronics vendors to get you to buy into their whole system of equipment.

But, if you are willing to forgo radar image overlay on your charts, you can have something that I think is even better using Coastal Explorer and many radars.  And it's all done using standard, non-propritary interfaces.  The key is the Target Tracking Message, or TTM.

Lots of radars, when tracking an ARPA target, send a periodic TTM message.  This message describes the target, it's position, it's tracked course and speed, and calculated CPA and TCPA.  It's basically all the info that your radar displays about a tracked target.  All you need to do is feed that message to CoastalExplorer via an 0183 port, and CE will display all those targets including their motion vectors.

Support for Target Tracking Message (TTM)?
Furuno FAR 2xx7 family
Yes (verified with CE)
Furuno 1835, 1935, 1945
Yes, with optional ARPA card installed.  (Verified with CE)
Furuno NavNet3D Family
Furuno TZTouch Family
Furuno FR8065, FR8125, FR8255
Simrad NSO EVO 2, NSS EVO 2
Raymarine Lighthouse 15
Manuals don't appear to list supported sentences, but some users report TTM supported on some models

My radars both display AIS targets, and of course display ARPA targets, so I can see both.  With a radar properly interfaced to CE, it too will display both AIS targets and ARPA targets, in context, on your chart.

In the screen shot below, we are approaching a fleet of a dozen fishing boats.  A few have AIS, but most do not, so I have acquired them with ARPA and am tracking them just like the AIS targets.

Approaching a fleet of fishing boats.

Now, in the shot below, you can seem them all on the chart as displayed by CoastalExplorer.  The AIS and ARPA targets are clearly distinguishable (blue vs red+green), and the ARPA targets faithfully reflect their status:

  • Round targets are acquired and tracking
  • The triangle coming towards us is a dangerous target
  • The square targets along the southern shore are still being acquired, so I know where they are, but I don't yet know their movement.

The same fleet on CoastalExplorer

To me, this now gives the best of all worlds.  My chart isn't cluttered up with radar echo returns, yet it  clearly shows the parts of the radar return that I care about and need to pay attention to, namely the ARPA targets.  And my radar screen is clear of chart clutter minimizing the risk that I will miss something.  With this arrangement, I no longer see any added value in radar overlay.

If I have you convinced this is a great feature, then read on about how to activate it.  It's very easy.

  • First, you need to confirm that your radar transmits TTM.  All that I've looked at do, but that's not an exhaustive list.  There might be some configuration settings in your radar to enable TTM, and you might need to set the baud rate.  Standard NMEA 0183 is 4800 bd, and high speed 0183 is 38kb (38,400 to be exact).
  • Next, figure out which output 0183 port you want to use on your radar.  You can use a free port, or you can use one that is already in use.  Multiple devices can listen to an 0183 channel, but only one can talk.  In this case, you need a port where the radar is the Talker.
  • Now you need to get the data from the radar into your computer running Coastal Explorer.  First check to see if there is already a port going into CE from your radar.  For example, if your radar is part of a multi-function chart plotting and radar system, you may well already be feeding data from it to CE.  If that's the case, then you already have the needed connection.  If not, you will need a free input port.
  • It's a bit of a side track, but the ports on your computer REALLY should be RS-422 ports (two signal wires for transmit, and two signal wires for receive) to be compatible and dependable with NMEA 0183 data.  Most PC ports are RS-232 (single signal wire in each direction) and they are NOT necessarily compatible.  You might get lucky and find it mostly works, but you also might not get lucky.  Or you may think it's working fine when it really isn't.  When I was experimenting with this last summer, the only interface device I could find in Juneau was an el-cheapo RS-232 interface adapter.  On the surface it appeared to work (my ARPA targets showed up on the CE screen), but when I used CE's TroubleShooting screen to examine the NMEA sentences coming in on the port, there were lots and lots of scrambled and corrupted sentences.  I now have a proper RS-422, and it is completely error-free.
  • If you need to make a new connection, run the wires and connect the Radar Talker wires (transmit) to the CE Listener (receive) wires.
  • To test, go to the Configuration page on CE, then click Troubleshooter.  Select the port number that you expect TTM to come in on, and click the Sentences tab.  The window will now show the NMEA sentences being received.  Acquire an ARPA target and you should start to see the TTM sentence coming in from the radar.  If there isn't a check mark next to the sentence, check it to enable it.
Good luck, and enjoy this hidden gem of a feature in CE.