OpenMarine

Hello every one,

The Garmin GPSMap chart plotter that i'm slowly replacing by OpenPlotter has this display of the sounder data:

[attachment=1535]

It also displays possible fishes when it finds them (although I guess there is some logic involved, not just data).

Assuming that I have NMEA0183 chart plotter's output connected to my RPi (and it's working, since I have depthBelowKeel message available in SignalK), is there any possiblity to have a similar display? 

If this already exists as OpenCPN plugin or SignalK app, and you tell where to find it, that'd be great, but after some research, that doesn't seem to exist, and I don't really understand why.

If I have to code it myself, could you point me out which nmea0183 sentences should I be looking for? Or if they are already handled by SignalK? I promise to share whatever solution I end up coding 

Well, if it's possible at all, because if it's not done, that could be a reason. 

Thanks!

NMEA0183 is not up to the task of decoding fishfinder information. That's not it's intent. With a fishfinder or other sounder device, there is usually a sonar module involved. I'm not familiar with your fishfinder, but when there is a sonar module involved (yours may be inside your unit, so I'll guess your transducer connects directly to the GPSMap?), there is usually some high bandwidth ethernet connection or video-type connection directly to or in the display. NMEA0183 is an ASCII text-based language that will never be able to decode that info. It's real purpose is to send the GPS & similar data it receives out to a VHF radio, laptop, or even SignalK. It operates at a very slow 4800 baud (0183HS is 38400 baud for AIS data).

Even DeviceNet (NMEA2000 at 250,000 baud) isn't up to the task of handling that big of data load. Fishfinders, like radars, require high-speed (ethernet or directly connected) interfaces with a device that understands how to decode that info.

Thanks SCarns, i didn't thought about the frequency, but it makes complete sense.
The sounder is connected to the GPSMap directly, and it allows the user to select both 50kHz and 200kHz, so indeed that's too much.

According to the manual, it can be connected to a CANet network, but i'm not sure to understand if that's the same as NMEA2k or some Garmin protocol.

But in any case, i assume the data would be in some propietary format, so I guess this answers why there are not OCpen/SignalK plugins for this

If it has a DeviceNet connector on it, I bet it is NMEA2k compliant. Hook it up and see what you get!

Honestly, I'm not sure about that :/

This is the available wiring:

[attachment=1538]

I already use NMEA Device 1 connection to get GPS position in the VHF (that was the only setup when I bought the boat) and depth messages in SignalK (with a 422 to USB converter). But the device doesn't have any N2K connection available. 

Ultimately, the goal is to connect the sounder directly to the RPi so I can get rid of this old plotter and use the space to install a nice touchscreen instead, so maybe I put the wrong focus