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Old 16-01-2019, 19:51   #1
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AIS Difference

Hi guys. I was looking for some input into my OpenCPN setup.

I have the following devices:

- Raymarine E7
- Raymarine Seatalk NG adapter
- Raymarine ST60 and ST600 (autopilot, wind, speed etc)
- TrueHeading AIS Graphine Plus Transponder
- Raspberry Pi 3B running Openplotter
- Actisense NGT-1

I have had the Openplotter working ok on my Pi with the GPS data coming through. Only thing thatís off is the heading data and True Wind Speed but COG, SOG and Apparent works perfect.

I recently connected my AIS via serial USB to the Pi and I am really happy to be getting AIS targets now showing.

The thing (see pictures) the number of boats showing in the same area on the Raymarine is much more than on the Pi. Itís about 10-15 ships different more than on Pi.

Does anyone know why this is?

I have checked the settings in OpenCPN and removed all the ones that might hide targets.

Appreciate any input.

Pi:

Click image for larger version

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Raymarine:

Click image for larger version

Name:	IMG_5026.jpg
Views:	103
Size:	433.3 KB
ID:	183960
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Old 16-01-2019, 22:19   #2
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Re: AIS Difference

The raymarine plotter keeping lost targets displayed longer? Nobody can tell you whatís really going on without access to your data.
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Old 17-01-2019, 05:37   #3
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Re: AIS Difference

I thought the same. However the picture above is in a big anchorage and both were turned on at the same time.

I was wondering if itís anything to do with data rates or setup issues.
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Old 17-01-2019, 06:15   #4
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Re: AIS Difference

Nobody will be able to tell you without access to your data. Check the lost target removal timeout for your plotter, if any, for OpenCPN the target is removed completely after not being seen for 10 minutes by default (Can be changed in Toolbox->Ships->AIS Targets)
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Old 17-01-2019, 11:13   #5
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Re: AIS Difference

As you can see in your image, opencpn has marked an ais target as lost, it is the one that marks the red arrow.



In a couple of minutes more it will eliminate it to avoid the clutter of the screen. If the plotter doesn't do it, or takes longer to do it, it is possible that this is the cause of the difference.

Look at the AIS targets on both devices but start them simultaneously and only after a couple of minutes of operation and see if they match.
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Old 18-01-2019, 08:48   #6
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Re: AIS Difference

Hi there,

So I did as you advised and started both systems at the same time. The Raymarine is still showing more targets.

I picked one target to look at that was showing as a lost target on OpenCPN and the ďlast seenĒ time was more recent for the Raymarine.

I have the USB connection set at the NMEA bauds of 38400.

Is it something to do with data rates or setup? I canít see why they would both have different data considering the source is the same unless OpenCPN (Openplotter) isnít getting the same data rate as the Raymarine.
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Old 18-01-2019, 10:15   #7
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Re: AIS Difference

Can you view the NMEA stream coming in with the debug window and see if some of them have errors? I think it shows them up in red.
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Old 26-01-2019, 09:27   #8
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Re: AIS Difference

@lawrence_craig


Your PI is not galvanic isolated from the Transponder I supose ?
Your plotter has a galvanic isolated optocoupler input.
If your Pi is lifted up or pulled down by some DC difference voltage, the serial input data can be distorted.


Be absolutly shure that the PI is at the samen DC level as the transponder without groundloops!
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Old 03-02-2019, 02:03   #9
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Re: AIS Difference

Quote:
Originally Posted by wad'nwind View Post
@lawrence_craig


Your PI is not galvanic isolated from the Transponder I supose ?
Your plotter has a galvanic isolated optocoupler input.
If your Pi is lifted up or pulled down by some DC difference voltage, the serial input data can be distorted.


Be absolutly shure that the PI is at the samen DC level as the transponder without groundloops!


I think this has hit the nail on the head.

How would you recommend resolving?
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