AIS Collision Warning for Own Boat . . .

[home_maarten]

Hi,

Have been searching the forum for threads on this topic, but couldn't find one covering it - if I missed, would appreciate if someone pointed me in the right direction.

Am using OpenCPN as additional/back-up navigation system on a netbook, and it has been working beautifully.

Being single-handed sailor, collision alarm capability was one of the main reasons to get AIS: comforting feeling that the system is constantly awake, even if I am not .

Now the problem I have - and this is both with OpenCPN and the additional set-up with chart plotters - is that I keep getting warned for my own boat, basically making the whole collision warning useless.

What I have is a Navico NAIS 300 AIS, combined with Lowrance HDS screens, and AIS input into Netbook with OpenCPN.

All systems show AIS target information well, and system is transmitting own ship AIS info.

Anyone know how to suppress warnings for own ship? Should be simple enough, with mmsi info readily available..

Hope someone can help - am about to start some major crossings, for which a fully working warning system would be very valuable .

Maarten

[bdbcat]

home_maarten...

Sounds a bit odd.
Could you describe your hardware and port setup, please?

Thanks
Dave

[home_maarten]

Hi Dave,

Thanks for the quick response.
Hardware set-up:
- NAIS 300 AIS transponder
- 2x Lowrance plotters (HDS7M and HDS8M)
- Above connected to a Shipmodul multiplexer, with USB output to HP netbook

The AIS GPS signal is also used by OpenCPN for position information, also coming through the USB output from the multiplexer. All works well (i.e. position, AIS info from other ships etc), except that I cannot use the alarm because it constantly warns me for myself. I agree that i may be the biggest danger to myself, but I already know that .

Would be great if you could help - if you need more data, let me know, but in itself the set-up is fairly straightforward.

Thanks so far!

Maarten

[bdbcat]

home_maarten....

Thanks for the info.

Could you capture and post a few minutes of the actual NMEA/AIS data stream coming into the PC?

Use Hyperterminal, or something similar....

Thanks
Dave

[bdbcat]

maarten....

Thanks for the logs.
I see the problem. There are two sources of ownship positioning info: the AIS VDO messages, and the multiplexed GPGLL/GPRMC messages. At any point in time, these two positions will not be exactly the same. In fact, while you are underway, sometimes the VDO position will be exactly one second in front of the GPGLL/RMC position, and on the same course line. You are going to hit yourself, very soon. So sad, we'll miss you....

Clearly a logic bug in opencpn, not seen before. Fix is easy. Look for it in the upcoming 2.3.1 update.

Quick fix for now with 2.3.0: If you can remove the GPGLL/GPRMC messages from the combined stream, the problem should disappear.

Dave

[home_maarten]

Dave,

Thanks a bunch... Actually have been wrestling with the NMEA sentences to let pass and the ones to filter: seems a lot of duplication, but on the other hand I have learned to be careful, because some instruments (like Navtex) can deal with only certain type of sentences, even if they contain the same info.

In this case this surprises me, because in OpenCPN, you have to indicate from which machine you tke the GPS info - in which I indicated AIS. Guess this is the bug you're referring, to, that in spite of this setting, it takes also position info from other sources?

Being a mechanical engineer (by training anyways, long time ago) this sort of bugs/debugging, apparently without real logic, drives me mad !

I'll give this a try anyway (have some other NMEA issues to fix, nothing to do with OpenCPN) and hope this works.

Thanks again for your time!

Maarten

[home_maarten]

PS... Would it not be easier to allow entry of own ship mmsi? Every system is bound (and desired) to habe some GPS/position information redundancy, won't it?

[bdbcat]

maarten....

There are of course lots of ways to fix this problem. Short term, I try to make the smallest possible change to the code, so that we don't need to go through a long Beta test cycle to validate the solution. That is what I have done here.

Longer term, we need to improve our NMEA/AIS data management and routing. There has been some recent discussion of this, and I expect it will come to life on the next Beta cycle.

The AIS issue only arises when the stream includes AIVDO messages .AND. other standard NMEA position messages. We (perhaps foolishly) add ownship to the AIS target list, and there it is just waiting to be a potential target to itself. Needs some more thought....


However, in the general case, if we process multiple positioning sources, there could reasonably be some "jitter" in the displayed ownship position. We need a priority scheme, and steering logic. That will come...

Good luck
Dave

[ozskipper]

HI guys. After watching this thread I googled and downloaded OpenCPN. Is there a place to download charts as well? I would like to have play with the software and get to know it. Thanks

Cheers
Oz

[ozskipper]

Also are there any recomendations. Raster vs Vector etc..

Cheers
Oz

[dacust]

Originally Posted by ozskipper

HI guys. After watching this thread I googled and downloaded OpenCPN. Is there a place to download charts as well? I would like to have play with the software and get to know it. Thanks

Cheers
Oz

Check the link in my signature. Free charts abound.

Originally Posted by ozskipper

Also are there any recomendations. Raster vs Vector etc..

Cheers
Oz

Use both. Learn the limitations and strengths of each.

Here is a start to explain a little about raster vs. vector, but it's about the types of errors, not really about the strength.

Inland Waters Resources - Chart Errors

-dan