Mark gaps in tracks

[hughfe]

The ADS-B trackers generally mark gaps in targets' tracks with dashed lines - is this practical with AIS-Catcher?
In my screenshot I lost coverage of Heritage Adventurer over about 4 miles, say about 20 minutes, and she would not have sailed straight over the mud flats. If the track gets broken for gaps of more than say 3 minutes when a transmission has definitely been missed.

[jvde-github]

Added. Good suggestion. You can set the threshold (in seconds) in the Settings menu (default is 30s)

[hughfe]

Nice. Thank you. I had to wait a while for something to get underway.
Since that was so easy ;) If you wanted to get really fancy you could set different thresholds for class A and class B signals. In fact if the track drawing routine can tell the difference, class A & B tracks could be different colours.....

[jvde-github]

That looks good on your example, thanks for sharing. What would be the application behind different colours for class A and B? We could link it to the ship type......

[hughfe]

Thanks. What led me to that idea was that the specified reporting intervals are different for class A & class B, so for a vessel with class A equipment underway the maximum reporting interval is 10 seconds, but for vessel with class B equipment underway the reporting interval could be as much as 3 minutes, so ideally the dash threshold would be different. Interestingly by distance class A vessels underway are required to report approximately every 70m, class B vessels between about 200 and 350 metres.
Which then led me to think it might be helpful to be able to distinguish class A & B at a glance, but maybe it's not that useful.
As you say, if it's practical to link colour(s) to ship type(s) there might be a use case for that. I think it would be quite neat - distinguishing say a pilot vessel's track from those of the tug and the vessel being assisted, but maybe this needs to be put to a wider audience before doing too much work on it.

[jvde-github]

I had a go last night at adding option to color tracks based on ship type. Has been running throughout the day without issues, so just committed. Looks nice. Not convinced about the different timing thresholds for class A and B, gets a bit messy. But the coloring is a great suggestion:

[hughfe]

That looks really cool! In hindsight I'm surprised no one thought of that before. Marinetraffic seem to vary track colour with ship speed, Vesseltracker just sets every track a different colour, but I think colouring by ship type like this might actually be useful.
If class B tracks are within view then the threshold has to be at least 30 seconds, but realistically there's no point in making it any less than that anyway, it wouldn't show anything useful and would just look messy.
Here I see two tugs returning down the harbour, Taiaroa has her AIS correctly programmed, the other one is Arihi and they have not programmed any ship particulars into the AIS, so it shows up as a pleasure craft - I've emailed the port manager but they don't seem to care!

[g7ruh]

@hughfe Great idea, thanks

Jasper, thanks for the quick turn-around on a proof of concept

Several thoughts / ideas. Maybe as options when using this to highlight tracks.

1. The track timeout is a bit short to show overall navigation channels. It may need to be a config option.

2. PlanePlotter has a "bread crumb" option where a position fix leaves a pixel (scaled to the zoom of the chart): big enough to see but not so big as to obscure other tracks. This is most useful in checking and comparing antenna patterns and different antenna locations. It needs to run for 24 / 48 hours to get good data. I do that sometimes for the aircraft, I miss a lot of signals to my north and west: a line of large oak trees act as signal attenuators!

A poor example but shows the gaps more accurately:

3. as @hughfe points out timings and power Class A to Class B are different. I would use the above to monitor Class B as I suspect some get drowned out by the Class A vessels. It would help to select Class A or B or all. Maybe selecting by vessel category would provide more flxibility, but a minimum of A and / or B would be needed.

4. the length of the dash is, I think, too long: it is hard to interpret the lost signal area: the breadcrumb trail would help. Maybe somewhere between the two is a sweet spot.

Regards
Roger

[jvde-github]

You can set the timing in the settings menu but don't think will add distinction for Class A and B. Can be done, but don't think the complexity is worth it.

On the pixels, get the idea but is the station page not showing the same, e.g. https://www.aiscatcher.org/stations/details/1909 or are you looking for a different visualization.

Will add some options to style the track dashing a bit more.

[g7ruh]

are you looking for a different visualization

Yes, a more detailed version of the max distance last hour / day pie chart. Run AIS-catcher with show all tracks on (no dashed lines) so it gives a coverage map based on my antenna position. Run it for several days to see every position decoded by my station. Take a screen grab of it. Change antenna position or new antenna and repeat the process. Then you can compare the two charts and it gives an indication of changes between the two setups.

Part of the reason for wanting to exclude Class A is there is so much more signal power it would distort the result (but also indicate the shipping lanes) You could color the pixels as per the track and that would give the same result: hence wanting a breadcrumb trail pixel-wise.

The Station page does not have the information and the max day / hour charts are lacking the granularity of the pixel per position report view.

Here is an hour or so from PlanePlotter with most of the A/C removed for clarity, when run for several days the outer reaches of the chart show obstructions to the signals. Change the setup and compare helps improve the station. One pixel per position report:

Here is part of the polar diagram showing maximum distance. That tends to be the highest aircraft. we are talking two dimensions, however tall vessels have a much longer range.

I appreciate atmospheric conditions can distort the results, but that does not happen too often.

Really just an aid to improving the system setup and being able to visualise the changes.