Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[Dockhead]

Originally Posted by rgleason

Yes, Dirk's algorithm is not (T)CPA but is a blended and prioritized filter which "Attenuates less important targets" (makes them smaller) to help declutter the screen.
I was thinking of a similar, but additive indicator of the most critical targets, using a similar process.

I think you are both suggesting that (T)CPA settings are what should be used, however we have many users that are complaining that those alerts go off all the time in very crowded situations, basically because small boats bounce around and don't have as stable instruments, so I was trying to find a good way to provide better information to those user by using Dirk's algorithm.

We have some nmea recordings of these AIS situations (start of a race) which are a good example of what happens in these situations.

Let's consider separately the case of alarms, versus the case of "attenuation", bolding, coloring, etc.

Alarms are simply not useful in cases where you are in crowded pilotage waters with vessels following channels and fairways and often coming on to momentary collision courses. Alarms are just meaningless in such situations, so just turn them off. The purpose in my opinion of a collision avoidance alarm is to call your attention to the screen when you are in more open water and not watching the traffic constantly. In crowded pilotage waters you simply don't need it -- your eyes are on the screen anyway.

Highlighting targets in some way -- even if it's a momentary situation which triggers it -- is no problem in my opinion. Let the flash red as they turn across your path -- I'd like to know about that actually. And go black again as they continue turning. Also attenuating them -- let them be un-attenuated if they turn in a way which causes a momentary conflict. What problem is that? I think it's actually good to see them.

It would be useful to be able to set the criteria for alarms separately from the criteria for visual indicators.


It might be nice to have some kind of super-highlighting for a target which seems especially dangerous -- CPA/TCPA criteria PLUS maybe fulfilling those criteria for a longer period of time, and/or stricter criteria like 10 minutes and 0.5 miles (for example) instead of 30 minutes and 1 mile (for example. Red flashing icon and/or a separate audio alarm. That would be great. That is the only feature I don't already have and would like to have.

[rgleason]

Thanks Dockhead. That's very useful.

[Juho]

Originally Posted by Dockhead

Let's consider separately the case of alarms, versus the case of "attenuation", bolding, coloring, etc.

I think one could develop an alarm system that could be useful also in crowded environments. I don't have much experience on what would be practical since I don't have AIS, but in theory this could work.

The basic idea is that there could be alarms e.g. when some new vessel seems to be more dangerous or about equally dangerous as the current most dangerous vessel is. This would be combined with bolding and colouring. I might tune the system so that after the first alarm (based on CPA and TCPA) the system would focus on the (max) three most dangerous vessels (that meet the original CPA and TCPS criteria), display them accordingly (highlighted), and give alarms (maybe not so loud) when there is something new to be noted. These new things to be noted could be e.g. "the most dangerous vessel has changed" and "new vessel in the top three". There would be some hysteresis in the system, and memory of the past given alerts and their timing, to avoid unnecessary alerts due to variation in the measurements and other minor changes in the environment.