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Old 19-10-2020, 16:11   #1
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Help with NMEA filtering

Hi,
O V5.2 and Win 10.

Have 3 inputs, Com 4 Vesper GPS/AIS (34.8)
Com 5 Simrad Autopilot (in/out and has the heading sensor)
Com 4 Garmin Depth/GPS.

All signals arriving and working in O, (with exception of route to autopilot; which is sketchy). Some say I have too many NMEA signals and should filter them. I do know where to add the filters, but am having troubles finding exactly which NMEA signals to accept or ignore. I have found the list of NMEA signals in directions/manuals but so far none seem to look like mine. Are there examples for this? I have also looked at 0183 sentences online, so have some familiarity, but am having trouble going from allowed signals to practice.

Since I'm struggling with Route to Auto, I'm going to start with these screens, in hopes somebody can put me on the right path.

First screen should show Communications Setup Com 5
Next screen NMEA output Com 5 with filtering
Com 5 with NO filtering

Thanks,

Armand
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Old 19-10-2020, 16:45   #2
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Re: Help with NMEA filtering

Armand,

there are a couple of places to look.

The first is the "priority" setting. This will "filter on the fly" if the same sentence is received from two sources. So, your Vesper and Garmin both send position, if they both send GLL then only the one with highest priority would be used by O. However, if one sends the position in GLL and the other in RMC then it will use both (and that can lead to things jumping around).

Then there are filters. I try to get information only once, but you need to decide what information you want. In your screen shots you have lat/long coming in RMC, GGA, GGL. I would review the additional information in those sentences and see if you use any of it, then filter away the ones you don't need. If you can filter so that you get the same information from two sources in the same sentences then the priority system will work better.

You could easily filter out RMB on Com3 (Vesper?), that sentence is empty, so no need to keep reading it (unless you are setting routes on that device and no route is active). And no need to pass that back out to Com5, it will just confuse things.

Lastly, on the output side, I would again review the sentences you are sending and only send the data your autopilot can use. And only send it once if you can. So, if RMC or RMB out contains all the information you need to send then get rid of any other sentences that have duplicate data.
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Old 19-10-2020, 21:35   #3
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Re: Help with NMEA filtering

Dsanduril,

Many thanks. I do have each port set with a priority, 3,2,1...Com 5 is set at 1 (which I understand is "backwards"...lowest... to many of us). I do not really understand the differences between GLL and RMC, so will do research (or just filter out and note any changes). Good suggestions...wish I knew more of this.

Thanks,

Armand

>>>>>>>

PS. I did halibut and trolling out of Juneau 20+ years ago. Love Petersburg...like everybody.
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Old 19-10-2020, 21:47   #4
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Re: Help with NMEA filtering

GLL and RMC are actually a really good example. GLL contains latitude, longitude, and time. RMC has all this information plus SOG, COG, date, and magnetic variation. So, if you are getting RMC from a GPS (GNSS in the new parlance) you really don’t need GLL.

GGA, on the other hand contains lat/long but also information on the fix quality, number of satellites, etc. So, the GGA position information is duplicative, but the rest is not.

The other thing would be to grab the Simrad manual and see what sentences it accepts. Probably all those you have shown, but no need to transmit data it will just ignore.

The common sentences are in the O wiki https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpnpencpn_user_manual:advanced_f eatures:nmea_sentences but there are more detailed references online if you want to dig deeper (sorry, on the tablet this evening, but I can list them tomorrow if you want/need them).
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Old 20-10-2020, 08:51   #5
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Re: Help with NMEA filtering

Quote:
Originally Posted by armand.seguin View Post
Hi,
O V5.2 and Win 10.

Have 3 inputs, Com 4 Vesper GPS/AIS (34.8)
Com 5 Simrad Autopilot (in/out and has the heading sensor)
Com 4 Garmin Depth/GPS.

All signals arriving and working in O, (with exception of route to autopilot; which is sketchy). Some say I have too many NMEA signals and should filter them. ................
Armand
Armand..
I'd have set filter and prioritization like this:
- COM? Garmin GPS Prio 3 No filter.
- COM? Vesper AIS Prio 2 Input filter: "[x] Ignore sentences" AIVDO
- COM 5 Simrad: Prio 1
No Input filter.
Output filter: "[x] Transmit sentences" First "Clear all" Then check ECRMB, ECRMC and ECAPB.

If you send out to much at baud rate 4800 your COM port will "choke" and be "sketchy" and this will hinder also the heading to be received.
Håkan
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Old 20-10-2020, 15:52   #6
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Re: Help with NMEA filtering

Quote:
Originally Posted by Hakan View Post
Armand..
I'd have set filter and prioritization like this:
- COM? Garmin GPS Prio 3 No filter.
- COM? Vesper AIS Prio 2 Input filter: "[x] Ignore sentences" AIVDO
- COM 5 Simrad: Prio 1
No Input filter.
Output filter: "[x] Transmit sentences" First "Clear all" Then check ECRMB, ECRMC and ECAPB.

If you send out to much at baud rate 4800 your COM port will "choke" and be "sketchy" and this will hinder also the heading to be received.
Håkan
Håkan,

Implemented all of your suggestions. Many thanks, as NMEA was about to overcome me! Excellent instructions.

I can send a Route to the Autopilot, and into to Dashboard, L/L, SOG, and Depth. Plus AIS targets on the chart.

Now I see AIVDO is own vessel (though it is still on the chart)

I will attach NMEA sentences Com 3 Garmin GPS/Depth FIRST

Com 4 Vesper AIS/GPS

Com 5 Simrad Autopilot

Wow, progress from the O community!

Tack,

Armand
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Old 20-10-2020, 22:24   #7
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Re: Help with NMEA filtering

Armand..
Good to hear, well done.
re: "Now I see AIVDO is own vessel (though it is still on the chart)"
Yes, own ship details are coming from the GPS and not AIVDO. I think it's corrected in OCPN code now but the AIVDO could make also an AIS target of your own ship that will confuse. That's why I, by historical reasons, use to filter that one out.


If you happens to install a wind instrument and want to use the AutoPilot's wind vane function you have to add the wind sentences to the COM5 output filter. (VWR)
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Old 21-10-2020, 20:56   #8
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Re: Help with NMEA filtering

Håkan,

Can't thank you and others enough. I did get the basics of O working without much help, but the multiple com ports and confusing (to me) NMEA signals had me tearing my hair out. Same with the overlay of the radar, which now works fine (though a bit mysteriously, as it went from skewed to just fine with no known input by me).

Very happy to have uncluttered NMEA screens, and all inputs working fine, and now the Routes too. A bit of work to do on importing of routes, but so happy they are now getting to the Autopilot (Robertson>Simrad>Navico!

Tack så mycket,

Armand
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