AIVDM, AIVDO and Own Ship GPS data

[Ptizef]

Hi

I installed recently an AIS transpondeur in place of my old Receiver.
Every things works fine and I have all AIS targets on the screen as before and may be better.
The GPS and AIS are connected to a Shipmodul Multiplexer. and My W10 is connected by USN, my Android tablet by WIFI. The GPS sentences from tha AIS are eliminated.
My problem is that since the installation of this new AIS, ownShip position became instable. I mean for example when the boat is not moving at all, OwnShip is always moving around the real position on the screen. I verified what receive O from My GPS and its very stable, not changing at all.
Then I blocked all sentences and re-allow them one afyer the other ... and I discovered that the problem came from the AIVDO and AIVDM setences.
If I start O receiving only these sentences, ownShip become red, the GPS status icone become green and OwnShip start swinging.
My question are
- Why these AIS sentences activate Ownship position?
- Could the sentences sent by my AIS be wrong ?

Thanks for your help
JP

Here an example of AIVDM - AIVDO received by O
<GREEN>21:15:47 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Gt3UMVl<CcQ3woQl000,0*1 6<0x0D><0x0A>
<GREEN>21:15:48 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Wt3UMVl<COQ3wp1l000,0*5 5<0x0D><0x0A>
<GREEN>21:15:49 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Wt3ULVl<CGQ3wpQl000,0*3 C<0x0D><0x0A>
<GREEN>21:15:50 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Wt3ULVl<CCQ3wpQl000,0*3 8<0x0D><0x0A>
<GREEN>21:15:50 (Serial:COM4) \s:MX27-2*46\!AIVDM,1,1,,B,402;bCQvFEC?iwgv;jKA5C7000S:,0* 1D<0x0D><0x0A>
<GREEN>21:15:51 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Wt3UL6l<BsQ3wq1l000,0*0 8<0x0D><0x0A>
<GREEN>21:15:52 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=00017t3UM6l<BoQ3wr1l000,0*7 7<0x0D><0x0A>
<GREEN>21:15:53 (Serial:COM4) \s:MX27-2*46\!AIVDM,1,1,,A,13IMQp001gOhTL8KBBS775gb08O3,0* 0C<0x0D><0x0A>
<GREEN>21:15:53 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=00017t3UO6l<C7Q3wrQl000,0*4 C<0x0D><0x0A>
<GREEN>21:15:53 (Serial:COM4) \s:MX27-2*46\!AIVDM,1,1,,B,D02;bCPVtLfq6DM6DA8u6D0,2*51<0x 0D><0x0A>
<GREEN>21:15:54 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0001Wt3UPVl<CCQ3ws1l000,0*4 6<0x0D><0x0A>
<GREEN>21:15:55 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0001Wt3UQVl<CSQ3ws1l000,0*5 7<0x0D><0x0A>
<GREEN>21:15:56 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0000Gt3UQ6l<CGQ3wsQl000,0*5 2<0x0D><0x0A>
<GREEN>21:15:57 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0001Gt3UR6l<C7Q3wtQl000,0*2 7<0x0D><0x0A>
<GREEN>21:15:58 (Serial:COM4) \s:MX27-2*46\!AIVDO,1,1,,,B3I?=0001Gt3UQ6l<BsQ3wu1l000,0*0 0<0x0D><0x0A>

[P_Dub]

have you tried to put the GPS on say com 5 or another com?

[Ptizef]

P Dub
The connexion is USB. The port COM is given automaticaly. Any way the connexion by WIFI is exactely the same

[Dsanduril]

The AIS transponder contains a GPS and sends your own boat position in the AIVDO sentence. If you also have a GPS sending position data for your own boat then you are getting the same data from two places and it will never be quite the same.

For each connection in O there is a priority setting that is intended to deal with duplicate data sets. But, it only works for the same NMEA sentence (for example two devices sending RMC). So, you have to ignore one position sentence. You can put either the AIVDO sentence on ignore or your GPS sentence(s). That should fix the instability. You only need the AIVDM sentences to get other boat data, which position information to select/use is up to you.

[Ptizef]

Many Thanks Dsanduril
I have my answer!
I didn't imagine that AIS specific sentence include own ship data
Blocking AIVDO solved the problem
JP

[rgleason]

Wiki FAQ How to block (filter) the AIVDO sentance?
https://opencpn.org/wiki/dokuwiki/do...aivdo_sentance

AIS Transponder and Ownship
https://opencpn.org/wiki/dokuwiki/do..._buttons:ais&s[]=aivdo#ais_transponder_and_ownship


Are these clear enough and adequate?

[Tehani]

Originally Posted by rgleason

Wiki FAQ How to block (filter) the AIVDO sentance?
https://opencpn.org/wiki/dokuwiki/do...aivdo_sentance

AIS Transponder and Ownship
https://opencpn.org/wiki/dokuwiki/do..._buttons:ais&s[]=aivdo#ais_transponder_and_ownship


Are these clear enough and adequate?

In any case, I think that the AIVDO sentence should always be filtered without the need for the user to configure it. I think it is quite useless information, and as we are seeing, it is also annoying.

[rgleason]

Agreed, It seems that it has no real purpose, yet requires user imvolvement and creates troubles..

[rgleason]

Here is a good point for keeping it as is:

There is good reason NOT to always filter AIVDO.
Some users prefer to use AIVDO, instead of some other GPS receiver's messages. They may be using an older receiver with low sensitivity, slow capture, etc.
The way I see it is this: Whether you know it or not, if you have an AIS transponder, then you have two GPS receivers. Only you (the user) can know which is to be preferred in your own environment.

[rgleason]

BTW Is this statement accurate with respect to AIVDO treatment in Opencpn?

AIS Transponder and Ownship


OpenCPN does NOT show Ownship (i.e. AIVDO message) as an AIS target or in the target list. AIVDO is processed only in the main navigation thread. The only true way to monitor the output of a transponder, is with a separate AIS receiver. Earlier releases did show ownship, but this was a bug, simply an illusion. The earlier presence of AIVDO (ownship) information in the data stream, really only indicated that the transponder was turned on and received GPS signals.


Question: This does not sound like the actions you are experiencing. How exactly is OpenCPN working now with respect to this.

[Tehani]

Originally Posted by rgleason

Here is a good point for keeping it as is:

Most AIS transponders, if not all, have an internal GPS receiver. And in them it is possible to enable the output of this data in standardized sentences (RMC, VTG, etc).
If the GPS receiver of those AIS devices is external, it is always better to connect it directly to the navigation system, making a bypass (parallel) to the plotter.
There are currently no devices that can take advantage of AIVDO for navigation. When a plotter or radio receives that sentence, without receiving the position data in GPS normalized sentences, they indicate "No FIX".
I still think that the AIVDO treatment creates confusion. I have never relayed that on my gateways and have never had complaints.

Note: Obviously I am talking about wired NMEA0183 networks. No additional connection is required on the NMEA2000 network.

[Tehani]

There is already enough confusion with redundancy of position data, COG / SOG and satellites in NMEA2000 when simultaneously connecting GNSS and AIS receivers with position output, or when connecting multiple GPS to OpenCPN. This problem has already been discussed: "The ship jumps across the screen".
We add display issues for our boat if we process AIVDO.

My advice is that those users who have an old GPS receiver, it is better to retire it and directly use the output of that data from their AIS transponder.
Normally, AIS transponders have two NMEA0183 output channels, one of high speed 38400baud, and another standard 4800 through which GPS data compatible with the AP and plotter can be output.

[Ptizef]

HI
To Rick : Every thing's OK for me now. I'am sorry, I hadn't read the manual before...
All unuseful sentences have been blocked in my Shipmodul multiplexer... and not only AIVDMO, but also all GPxxx from the AIS. (I prefere GPS fix from my (quit) old Garmin GP152 which I absolutely trust)
I have previously thought to connect my transceiver in NMEA 2000 but I did'nt find the solution to block the redundant sentences. If someone has the solution...
And I agree with what is written above : I can't find what is the purpose of AIVDO, and in what it could be useful. but I'am not a NMEA specialist.
JP

[Tehani]

Originally Posted by Ptizef

I have previously thought to connect my transceiver in NMEA 2000 but I did'nt find the solution to block the redundant sentences. If someone has the solution...
And I agree with what is written above : I can't find what is the purpose of AIVDO, and in what it could be useful. but I'am not a NMEA specialist.
JP

Here started a conversation related to that topic:

https://www.cruisersforum.com/forums...ml#post3328697

[barnakiel]

You can place the USB on another COM. If this matters at all.


The system assigns something by default. But it is not a fixed thing. You can change it in settings.


b.