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Old 23-08-2022, 14:53   #1
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Fatal Flaw in Standard Horizon Matrix AIS.

Compare the two attached pictures, one from the Standard Horizon Matrix VHF and one from OpenCpn. Note that the VHF display shows a healthy CPA equal to the range of the other vessel. Note that the OpenCPN display shows a very unhealthy CPA of 0.12 miles from a vessel whose length is about 0.12 miles.

If you depended on the Standard Horizon, you could be dead.

I do have similar pictures for another vessel.
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Old 23-08-2022, 15:46   #2
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

I've recently learned how to use the tracking feature on my radar.

Works much better than AIS, although I still use the AIS to label targets.
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Old 23-08-2022, 15:53   #3
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

~2hr to the CPA, one would hope someone would do a visual before then to confirm the electronics
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Old 23-08-2022, 16:24   #4
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

How do you know the SH is in error and not the OCPN?

The little 'heading marker' on the Pan Gloris on the SH display shows her on a diverging course.

What was the end result? Did she run you over?

Interesting - one display says 12.5 CPA .. the others says .12
Is that a coincidence?
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Old 23-08-2022, 17:52   #5
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

The 12.5 vs 0.12 is suspicious, but could be a coincidence. If you share your own course and speed at the time, we can do a manual plot to see which of the two is wonky.

If one of the vessels is turning, then I'd wait for things to settle before trusting the computation.
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Old 23-08-2022, 17:56   #6
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

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Originally Posted by capn_billl View Post
I've recently learned how to use the tracking feature on my radar.

Works much better than AIS, although I still use the AIS to label targets.
It becomes a winner when the radar is able to link AIS targets to radar echoes and present them as a single symbol. I think my simple 4G can do that.
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Old 24-08-2022, 12:59   #7
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

Here is the other incident. Note that the Std Horizon CPA again defaults to the range. In this case it was clearly a crossing situation, and there is no doubt the CPA cannot be the range.

In the first incident, there was clearly a collision problem, and we turned 10 degrees to starboard even though the other vessel was overtaking. We were going 6-7 knots at the time.

In the second incident, the other vessel was a long tow, and I could see him slow down and turn to starboard to give us a 2 mile CPA.

I really don't care if the Std Horizon later recalculates a correct CPA. I am trying to identify problem vessels vs no problem vessels and focus on the problem vessels. I think the Matrix units should be recalled.
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Old 24-08-2022, 13:30   #8
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

It is possible to have identical CPA and Range if it is at CPA at the time of observation eg overtaking ship on parallel course when on the beam.

However this isn't the case with yours. Maybe an isolated software issue - dunno.

Does it happen with every contact or is it intermittent ?

I'd be getting in touch with SH for sure.
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Old 24-08-2022, 13:51   #9
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

I've been using mine for about 5 years and have never seen this error. I'll keep an eye out for it, but as my unit is a bit old it may not have the same software version that you have.
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Old 24-08-2022, 14:13   #10
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

Agree, this looks problematic. Even if it lacked sufficient data to complete the calculation, it shouldn't default to the distance value.

If it did later correct itself, how long did that take?
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Old 24-08-2022, 14:16   #11
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

Quote:
Originally Posted by donradcliffe View Post
Here is the other incident. Note that the Std Horizon CPA again defaults to the range. In this case it was clearly a crossing situation, and there is no doubt the CPA cannot be the range.

In the first incident, there was clearly a collision problem, and we turned 10 degrees to starboard even though the other vessel was overtaking. We were going 6-7 knots at the time.

In the second incident, the other vessel was a long tow, and I could see him slow down and turn to starboard to give us a 2 mile CPA.

I really don't care if the Std Horizon later recalculates a correct CPA. I am trying to identify problem vessels vs no problem vessels and focus on the problem vessels. I think the Matrix units should be recalled.
Yes, you need to give us your course and speed. My first thought is that the Matrix Radio is not getting proper own ship GPS information and/or not calculating ownship course and speed.
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Old 24-08-2022, 20:08   #12
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

Looks to me like a display bug where it's displaying RNG in place of CPA. If would be interesting to see if it alarms based on the correct CPA, or the faulty one begin displayed.


What firmware revision do you have?
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Old 24-08-2022, 20:42   #13
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

I have been using the Standard Horizon AIS for 5 years, and crossed hundreds of vessels and not seen this. I use the AIS alarm on SH instead of OpenCPN, but always compare them when an alarm goes off.

Before you blame SH, you need to capture the AIS data for evaluation. You can record it in OpenCPN with the VDR plugin. It would then also be possible to rig a setup to play the NMEA data back to reproduce the error on the SH.

I *HAVE* had a few times a ship was transmitting invalid data that resulted in incorrect display.
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Old 24-08-2022, 20:52   #14
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

One possible cause. Are you using an external GPS/Antenna with the SH? If not, then the GPS signal could be weak or sporadic, and at times report your boat going the incorrect direction. If you are moving away from each other, then the Range will be the CPA.

While I never observed the issue you have, I did find that overall it worked much better when receiving GPS from the boats external antenna, and not relying on the internal GPS.
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Old 24-08-2022, 23:49   #15
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Re: Fatal Flaw in Standard Horizon Matrix AIS.

The cause of this difference is not any flaw in the SH unit; it's just that you are more than 2 hours from CPA, so the CPA will vary wildly based on small changes of SOG or COG of either vessel. This information is not really usable that far off. The SH is just using a different slice of data.



I wouldn't even pay attention to this until you are one hour TCPA. If you're getting less than 2 miles CPA at one hour TCPA, then start watching it. By half hour TCPA it's time to start planning your action.


As to using radar -- not all vessels transmit AIS, so you should watch that too. But MARPA is much less accurate than AIS with radars and compasses like what we have (big ship radar is different). So if you have both AIS data and MARPA data, you should give priority to the AIS data.


OpenCPN has a superior AIS implementation with really useful presentation of the geometry of the crossing with a target (right click, choose "display target CPA" to get this). In high traffic areas like German Bight, English Channel, etc., I like to have someone at the helm keeping a visual watch while I do collision avoidance at the nav table. I use AIS on OpenCPN and keep the nav table MFD on the radar display. MARPA is working better on my system since I changed my compass, but I still don't like it much. I prefer to do manual plotting with a pencil on a plotter sheet, or just use EBL and VRM on the radar display. Watching the target move in relation to the EBL is a really analogue way to do it, but works extremely well. You don't actually need to know to the meter or even to the cable what is the CPA, to distinguish a safe from unsafe crossing, or to know what to do.


I recently had to refresh these skills when I spent the entire summer last year -- a few thousand miles in busy waters including a long distance ocean race -- without AIS at all (which failed at the beginning of the summer and then I was unable to get a new one delivered anywhere in time). It was good to be reminded that you can do entirely satisfactory collision avoidance without AIS, if you have reasonable radar skills.
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