Quandary about 3G/4G MARPA on Navico
Thanks to the brilliant work by the Daves and Kees we now have good functional radar plugins for both the Garmin and the Navico/Lowrance/Simrad/B&G 3G/4G radar.
I have an older boat with a lot of NMEA0183 and no NMEA2000. The quandary is about MARPA. If you don't care about MARPA you can buy a simple standalone 3G Navico
radome and plug
the ethernet cable into a local hub and voila, radar. Even with the state of today's plugins this would give you basic radar functionality in OpenCPN and I'm sure that the plugins will only get more refined over time. To be explicit: the radar internet
cable from the radome is a combined ethernet cable and a power cable. As long as you provide some power down the red, yellow and black wires and have a hub, that's all you need.
What if you want MARPA? On the Navico radars (they're all the same regardless of whether they are called Simrad/B&G/Lowrance) you need to inject a NMEA2000 signal into the radar. The radar acts as a server and handles the tracking of MARPA targets. Presumably we have to tell the radar which targets to track. Of course, we don't yet have any MARPA functionality in the current
plugins, but this would represent the official Navico way of handling MARPA.
In order to do this injection you also need two more physical parts
: (a) a RL10 interface box and (b) a NMEA2000 to Simnet converter kit.
I should note that looking at Defender it appears difficult to buy a 4G radome without the RL10 box.
Of course, you also need a NMEA2000 stream which, if you don't already have, you can get opensource through CANBOAT and an Activesense NPT1 dongle or from Navico with a RL11 interface box and a NMEA
converter for heading data (an AT10HD). It isn't clear whether the latter option would actually provide all the necessary information for the radar to do MARPA.
All told, the hardware
for the injection of the NMEA2000 data into the radar would add a fair amount of complexity and dollars to the basic radome.
So, finally, the question....is there a clear path ahead for OpenCPN plugins and MARPA? It would seem like there could be four future approaches:
(1) Don't handle MARPA at all in OpenCPN and leave it to any attached MFD.
(2) Support the MARPA calculations produced by the radome - i.e. use all the Navico hardware
- and have OpenCPN tell the radome which targets to track.
(3) Do MARPA entirely in software
inside OpenCPN so that MARPA is independent of the radome. This would presumably mean discriminating between the different moving blobs - don't know if this is possible.
(4) Figure out a way to inject the necessary heading data into the ethernet stream inside the plugin so that the RL10 is not needed.
For those of us toying with purchasing
hardware, can the developers give us any hints which way forward is most likely and practical? I'm not asking for MARPA capability now though I am hoping for it sometime. Rather I'd like to try to futureproof my expenditures.