Display of AIS AtoN on Lowrance HDS-8

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 6:48 am

This series of article describes results of a test using the Lowrance HDS-8 first-generation chart plotter to show AIS Aid-to-Navigation Synthetic marks received from USCG AIS stations in the Great Lakes. The results of the test are very positive and encouraging, considering the age of the chart plotter and the long time since a firmware update for it was provided by the manufacturer.

The United States Coast Guard (USCG) has begun to use the Automatic Identification System to send electronic Aids to Navigation (AIS AtoN) to supplement the physical buoys in the Great Lakes. Just recently, the USCG began transmitting AIS messages sending Message 21 for AIS AtoN navigation aids. I was curious if I could receive these AIS signals on my em-trak R100 AIS receiver, connect the NMEA-0183 data output of the AIS receiver to my Lowrance HDS-8 chart plotter, and observe how these electronic buoys were represented on the electronic chart display of the HDS-8.

Receiving the AIS AtoN signals in my region was not a problem. They are being sent from an N-AIS base station co-located at RESCUE 21 site RFF WAYNE, about 18-miles away from me, originating from a very tall (about 300-feet high) tower. The AIS signals were easily received at my location on an indoor antenna.

My HDS-8 chart plotter is a first-generation device. There has not been any firmware update for it from Lowrance since Februay 2012, almost four years ago. I was skeptical the HDS-8 would have the capability to show AIS AtoN icons because, at the time of the last firmware update, there were practically no such devices in use in the USA. I was very pleasantly surprised to find that my first-generation Lowrance HDS-8 was quite capable of displaying AIS AtoN targets. I demonstrate its capabilities with several screen captures.

shot 11.png
shot 11.png (42.9 KiB) Viewed 15403 times
HDS-8 presentation of AIS AtoN targets.

In the above screen capture, 15 AIS AtoN aids to navigation are shown. Not shown are about five more AIS AtoN marks in the lower Detroit River and Lake Erie. The targets in Lake Huron are over 50-miles from my receiver, but the actual signals for them are originating from the much closer tower at RFF WAYNE.

Having crossed the hurdle of receiving the AIS AtoN signals and seeing them on the chart plotter, the iconic representation of the aid to navigation was the next area of interest. As shown above, the aids are represented by a black rhombus with an internal black crosshair mark. Guidance for how AIS AtoN targets ought to be shown on electronic chart plotters is given by IEC Recommendation 68822. The basic AIS AtoN symbol is a diamond or rhombus shape with a black crosshair in the center, drawn with thin solid black lines. The applicable text from the recommendation says:
Real or synthetic AIS aids to navigation
(AtoN) shall be presented as a diamond with
crossed lines centred at the reported position
of the AtoN. The crossed lines shall be not
more than 2 mm in length and the sides of
the diamond shall be not more than 6 mm in
length.

The diamond and crossed lines shall be
drawn using a thin solid line style.

The symbol representations for a real or synthetic AIS AtoN should look like this:
IEC6288Page76AIS_Real_SyntheticAtoN_Symbols.jpg
IEC6288Page76AIS_Real_SyntheticAtoN_Symbols.jpg (18.48 KiB) Viewed 15286 times
Recommended symbols for Real or Synthetic AIS AtoN

Before we can assess the Lowrance HDS-8 display and its compliance with recommendations, we must first identify the type of AIS AtoN that is being received.

[Article continues below]

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 7:14 am

There are three categories of AIS Aids to Navigation: real, synthetic, and virtual. Again, the USCG announcement explains the difference:

These broadcasts can originate from an AIS station located on an existing physical aid to navigation (Real AIS AtoN) or from another location (i.e., AIS Base Station). An AIS Base Station signal broadcasted to coincide with an existing physical aid to navigation is known as a Synthetic AIS AtoN. An electronically charted, but non-existent as a physical aid to navigation, is identified as a Virtual AIS AtoN.


Based on the above criteria, it would seem that the signals being sent from the AIS AtoN received in my test are likely to be Synthetic AIS AtoN signals, that is, the signals are sent from a Base Station and are meant to coincide with the location of an actual physical aid to navigation. On that basis we can assess the Lowrance representation of the Synthetic AIS AtoN signals.

UPDATED: It appears that in the Lowrance HDS-8 first generation, a Synthetic AIS AtoN is being represented by the most basic icon, just as recommend by the IEC-62288 document (see above).

shot 14.png
shot 14.png (38.72 KiB) Viewed 15402 times
The AIS AtoN for a Synthetic Aid, as rendered on the Lowrance HDS-8 first generation chart plotter with the INSIGHT USA optional charts loaded.

In the HDS-8 chart display, AIS AtoN icons are overlaid on other chart details, so they typically land right atop the charted aid to navigation, as seen above. If the cursor of the chart plotter is moved over the AIS target, an identifying banner will appear.

shot 16.png
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Banner text appears giving the identity of the AIS AtoN target if the cursor is moved to the target

The above screen capture shows the BELLE ISLE NORTH LIGHTED BUOY 113 identified in abbreviated text. If the ENTER button on the HDS is depressed when the cursor is on the target, a details page appears, giving more information on the target.

shot 18.png
shot 18.png (66.17 KiB) Viewed 15402 times
AIS Aid To Navigation (ATON) Details screen

The details screen gives the MMSI of the AIS AtoN and its position, and several other parameters sent in the AIS transmission; see below for the complete list of data that is shown. Note that a range and bearing are not shown; at the moment I took this screen capture my chart plotter had not acquired its own position, so it could not compute a range and bearing to this target.

Overall I am quite pleased with the performance of my first-generation HDS-8 chart plotter and its handling of AIS AtoN signals. I really did not have great expectations for its ability to show AIS AtoN targets due to the age of its firmware. The deployment of AIS AtoN signals in the Great Lakes and elsewhere by the USCG is still in a testing phase, I believe, and I am, again, very pleasantly surprised that the four-year-old firmware in the first-generation HDS-8 is even attempting to show these targets.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 10:25 am

ASIDE: ON CONNECTING THE AIS RECEIVER AND CHART PLOTTER:

I was able to connect the NMEA-0183 output of my em-trak R100 receiver to the NMEA-0183 input of my Lowrance HDS-8 chart plotter with very little fuss because previously I had wired both interfaces with my UNIVERSAL NMEA-0183 INTERFACE connector and signal layout. To get the two devices talking was just a simple matter of plugging their universally wired connectors into the appropriate ports of my NMEA-0183 universal backplane connector. The total amount of time spent in making these two device communicate was literally about 30 seconds--the time it took to plug the two connectors onto the universal backplane interconnecting device.

You can read more about my NMEA-0183 UNIVERSAL CONNECTION system in the REFERENCE section:

http://continuouswave.com/whaler/reference/UniversalNMEA0183.html

porthole
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby porthole » Sat Dec 05, 2015 12:24 pm

If I see it correctly, the AIS AtoNs are represented on your plotter as either Real or Synthetic. How did you determine the transmission is coming from the Rescue 21 tower and not the actual aid?

I do not know how my radio is receiving the AIS transmissions, only that it is. I thought there must be some type of relay with the Rescue 21 system, as we have four towers in New Jersey, one only a few miles from me and one is in between me and the Ambrose Channel AtoNs.

My Standard Horizon GX-2200 is only using a GAM ELECTRONICS SS-2 VHF antenna. Even if the antenna is laid down, I still receive AIS info on the radio and plotter, including the 24-mile-away Ambrose AtoNs.
Thanks,
Duane
1999 Outrage 21
1999 Yamaha SW Series II 200

porthole
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby porthole » Sat Dec 05, 2015 12:26 pm

Did you try and bring up the actual AtoN info page, meaning not the AIS page?

I had to click outside the AtoN icon, clicking on the number to get the info page.
Thanks,
Duane
1999 Outrage 21
1999 Yamaha SW Series II 200

jimh
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 1:20 pm

How did you determine the transmission is coming from the Rescue 21 tower and not the actual aid?


The signal I am receiving--and most likely the ones you are, too--cannot be coming from the actual aids because of the impossibility of receiving them at the distance my receiver is located from them, the height of my antenna, the height of the transmitting antenna, the power of the transmitter, and the accompanying path loss. AIS AtoN signals coming from a floating aid [or the short tower of a fixed aid] would have to be powered by a battery that is recharged by a photo-voltaic panel. I doubt the electrical power budget for such as system could afford to send a 25-watt signal. Most real AIS AtoN signals will probably be more like 2-Watt signals. The antenna height would be low, from only be a few feet above the water for a floating aid to perhaps 25-feet for a fixed aid with a tower. The radio horizon for such a signal would only be a few miles. The AIS AtoN signals from Lake Huron are over 56-miles away.

Having monitored for AIS signals from my location before, I know I cannot even receive a CLASS-A AIS transmission from a commercial ship with an antenna mast that is probably 50-feet above the water using my indoor antenna. The path to these signals from my location is across urban terrain with many tall buildings. The signals are all synthetic AIS signals and are being sent from RFF WAYNE as part of the N-AIS program.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 2:03 pm

Did you try and bring up the actual AtoN info page, meaning not the AIS page?


[I deleted a sidebar discussion with some back and forth until I figured out what PORTHOLE was really asking. He also explained a bit about how his newer Lowrance chart handled AIS AtoN display. See his separate thread about the newer Lowrance Gen3 chart plotter for his screen captures and a good explanation of how to get to the physical aid information page instead of the AIS Details page on that newer plotter.]

OK--now I see your question more clearly: you are asking about the actual physical aid to navigation information, not the AIS AtoN. Sorry, but I misread your question the first five times I read it.

Because the AIS symbol is overlaid on the chart symbol, it is hard to get to the information about the physical aid by positioning the cursor to be on the chart symbol instead of the AIS overlaid symbol. I had to zoom in to a very large scale display in order to get a bit of separation between the icons for the chart's aid and the AIS overlaid aid. Then I could reach the information page by putting the cursor on the charted aid and hitting ENTER.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 2:09 pm

Ahah! I found the trick to get to the information page for a navigation buoy that has an AIS AtoN symbol overlaid. To get to either the AIS AtoN Detail page or the regular chart physical buoy information page on the HDS-8 first generation, you have to:

--put the cursor over the icon for the aid to navigation

--push the MENU key

--a contextual menu pops up; in the menu are two choices: AIS DETAILS or INFO.

Use the cursor keys to highlight AIS DETAILS:

contextualMenuAISdetail.png
contextualMenuAISdetail.png (7.11 KiB) Viewed 15270 times


If you then push ENTER, you will get the AIS DETAILS screen:

Image

While on the contextual menu, you can alternatively highlight the INFO choice:

contextualMenuINFO.png
contextualMenuINFO.png (6.99 KiB) Viewed 15270 times


If you then push ENTER you will get the Chart information screen:

ChartInfo.png
ChartInfo.png (17.79 KiB) Viewed 15270 times

On the INFO page you will see the physical characteristics of the aid to navigation (like color, name, light characteristics, and so on). Note the on-screen soft-key button DETAIL; pushing it will also take you to the AIS DETAILS. They forgot to include the corresponding button on the AIS DETAILS page to get to the INFO page.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sat Dec 05, 2015 9:11 pm

The AIS INFORMATION page for an AIS AtoN on a Lowrance HDS first-generation chart plotter shows the following eight data values being sent in the AIS Message 21 broadcast:

--MMSI of the AIS AtoN
--nature and type of aid (from 32 categories, see below)
--name of the aid to navigation
--position accuracy
--position latitude
--position longitude
--off-position indicator
--status

The categories for nature and type of aid are given in ITU-R M.1371-5 Section 3.19 in Table 74, and are reproduced below:

0 = Default, Type of AtoN not specified
1 = Reference point
2 = RACON
3 = Fixed structures off-shore, such as oil platforms, wind farms. (Should identify an obstruction that is fitted with an AtoN AIS station)
4 = Spare, Reserved for future use

FIXED AtoN

5 = Light, without sectors
6 = Light, with sectors
7= Leading Light Front
8 = Leading Light Rear
9= Beacon, Cardinal N
10 = Beacon, Cardinal E
11 = Beacon, Cardinal S
12 = Beacon, Cardinal W
13 = Beacon, Port hand
14 = Beacon, Starboard hand
15 = Beacon, Preferred Channel port hand
16 = Beacon, Preferred Channel starboard hand
17 = Beacon, Isolated danger
18 = Beacon, Safe water
19 = Beacon, Special mark

FLOATING AtoN

20 = Cardinal Mark N
21 = Cardinal Mark E
22 = Cardinal Mark S
23 = Cardinal Mark W
24 = Port hand Mark
25 = Starboard hand Mark
26 = Preferred Channel Port hand
27 = Preferred Channel Starboard hand
28 = Isolated danger
29 = Safe Water
30 = Special Mark
31 = Light Vessel/LANBY/Rigs

The data field "status" does not seem to be specifically defined in any reference material I can find. It is shown as "Safe" in most instances I have encountered, but I don't know what the other options might be.

There is a bit more information being sent (in the AIS Message #21), but the Lowrance HDS is showing most of it. The information page also computes:

--the distance to the aid
--the bearing to the aid
--the point of closest approach
--the time of closest approach

These data are not sent from the AIS AtoN but are calculated by the chart plotter.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Mon Dec 07, 2015 8:22 am

For those curious about more technical details regarding AIS AtoN signals, you can obtain on-line and at no cost the actual International Telecommunication Union (ITU) recommended practices document R-REC-M.1371, Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile frequency band.

See Section 3.19 Message 21: Aids-to-navigation report. There TABLE 73 lists all the data parameters being sent.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Tue Dec 08, 2015 1:14 pm

In the case of AIS AtoN signal of the real and synthetic category, there is a physical aid on the water that corresponds to the electronic marker signal being sent. In the case of a virtual AIS AtoN, there is no equivalent physical aid on the water. Just recently I was explaining these three categories to another mariner--my lovely wife and boating partner Chris--and she made a very cogent observation. She said something like, "It would be very confusing to see an AIS AtoN symbol on the chart plotter, and when you approached that location not see any buoy on the water."

Chris's remark was really very instructive for me. It made me realize the symbols used on a chart plotter to represent a virtual AIS AtoN ought to provide a clear distinction from the other two categories, real and synthetic, because for those two types of AIS AtoN there will be a physical buoy or structure at the location of the AIS signal.

The recommendations from IEC 62288 suggest a distinctive marking; the black diamond is to be drawn with dashed lines, not solid lines. Here is the applicable text from the recommendation:

Virtual AIS aids to navigation (AtoN) shall be
presented as a diamond with crossed lines
centred at the reported position of the AtoN...

The diamond shall be drawn using a thin
dashed line style. The crossed lines shall be
drawn using a thin solid line style.


The symbol representation should appear as shown below:

IEC6288Page77AIS_VirtualAtoN_Symbols.jpg
IEC6288Page77AIS_VirtualAtoN_Symbols.jpg (18.15 KiB) Viewed 15291 times
AIS AtoN Symbols for Virtual Aids

In my testing so far, I do not believe I have encountered a virtual AIS AtoN signal, so I don't know how it will be rendered on my Lowrance HDS first-generation chart plotter display.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Fri Dec 11, 2015 12:00 pm

Just when you thought this thread could not get any better: I found an VIRTUAL AIS AtoN signal in my area! As it happens, I can also receive AIS signals for many, many AIS AtoN electronic navigation marks in Lake Erie recently added by the USCG to their testing. Some of them are virtual AIS AtoNs, that is, there is no longer a physical aid to navigation at the location, but just the electronic marker being send via radio. A listing in the Local Notice to Mariners (LNM) gave me the location of an in-range virtual AIS AtoN:

Maumee Bay Lighted Buoy “21” (LLNR 6155) Virtual AIS ATON


I was delighted to find that I could receive the AIS signal for this aid. This provides the opportunity to further test the chart plotter's representation. Because this is a virtual aid-to-navigation, its symbol should distinguish it from a real or synthetic aid-to-navigation. The screen captures below show how the first-generation Lowrance HDS-8 chart plotter rendered the data.

1MaumeeBayLB21ChartedView.png
1MaumeeBayLB21ChartedView.png (47.81 KiB) Viewed 15265 times
HDS-8 chart view of Maumee Bay Lighted Buoy 21 with AIS overlay

The AIS AtoN symbol appears to be the same basic symbol used for real or synthetic AIS AtoN electronic marks. According to recommendations, this symbol should be drawn with dashed lines for the diamond or rhombus.

2MaumeeBayLB21Zoom.png
2MaumeeBayLB21Zoom.png (16.86 KiB) Viewed 15265 times
As above, but with a larger scale chart presentation

There is no sign of any dashed lines in the drawing of the rhombus symbol. Moving the chart cursor over the symbol brings up an identification banner:

3MaumeeBayLB21Banner.png
3MaumeeBayLB21Banner.png (17.83 KiB) Viewed 15265 times
HDS-8 shows the identity of the navigation mark when the cursor is positioned on it

So far there is no sign that this aid-to-navigation is a virtual AIS AtoN.

The electronic chart continues to show a floating aid to navigation at that position. This is to be expected because when the chart was created, there was a floating aid at that position. The chart would have no way to modify its position based on a Notice to Mariners that the floating aid was being removed for the winter season by the Coast Guard, so the chart still shows a physical aid in that location.

[Continues in next posting]

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Fri Dec 11, 2015 12:10 pm

As already mentioned, when an AIS symbol overlays a chart object, you can get to the two separate information or detail pages, one for the AIS target and another for the chart object, by using the contextual menu for that presentation. (ASIDE: the term "contextual menu" refers to the concept that the contents of the menu will change depending on the context or situation in which the menu is called upon for display. In this case, when an AIS object is part of the chart area under the cursor, the menu adds an option for AIS detail. On the HDS-8 the contextual menu is invoked by hitting the MENU button.)

Selecting the AIS DETAIL option from the contextual menu gives this page of data:

4MaumeeBayLB21AISDetail.png
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AIS Detail Page for virtual AIS AtoN

There does not appear to be any indication in the AIS DETAIL page that this AIS AtoN is of the category virtual. The information presented is the same as was given for synthetic AIS AtoNs.

Selecting the INFO option from the contextual menu gives this page of data:

5MaumeeBayLB21ChartInfo.png
5MaumeeBayLB21ChartInfo.png (20.06 KiB) Viewed 15265 times
Chart Info Page for the charted object

So far as I can tell from this example, the first-generation Lowrance HDS chart plotter is not drawing the electronic chart symbol or presenting information details for a virtual AIS AtoN in any different manner from a real or synthetic AIS AtoN. While this is a slight disappointment, I still am impressed overall with the ability of the first-generation HDS to show these electronic navigation marks.

ASIDE: I have not captured and analyzed the AIS Message 21 data that is actually being sent to verify that the actual data contained in the radio signal does indicate a virtual aid category for this mark. I am assuming the USCG is transmitting it as a virtual AIS AtoN based on the notice to mariners.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sun Dec 13, 2015 12:38 pm

To complete my testing of how the Lowrance HDS first generation chart plotter renders AIS AtoN signals into chart presentation, I checked the presentation when using a different electronic chart. The results were interesting. Compare the prior screen captures with this one:

shot 38.png
shot 38.png (40.6 KiB) Viewed 15246 times
Lake Huron Cut Buoys 11 and 12, Navionics Chart with AIS AtoN symbols showing

The above screen capture shows two synthetic AIS AtoNs in Lake Huron as presented with a Navionics chart. The most remarkable difference involves the way the AIS AtoN diamond symbol is drawn for the electronic aid with respect to the chart's own symbol for the physical aid. In this presentation, the AIS AtoN symbol is drawn underneath or behind the chart symbol for the physical aid. This presentation is the opposite of that seen earlier. In those earlier screen captures, the chart in use was the Lowrance built-in chart. (My HDS-8 has the upgraded option for included USA charts called "INSIGHT USA" charts.) The electronic marker (black diamond) was drawn over the chart marker on those Lowrance charts. On this Navionics chart, the electronic marker (black diamond) is drawn behind the chart marker. This presentation does not obscure the original chart icon for the marker.

I assume the difference in presentation must be related to the structure of the electronic data in the charts in particular layers or tiers, and in the Navionics charts the AIS overlay layer must be underneath the chart buoy icon layer.

ASIDE: About a week ago, when I first began this testing process, I noticed that there was an error in the position of the AIS AtoN for Lake Huron Cut LB 12. The electronic position for this aid was being sent with the latitude off by about two miles. I called the local USCG facility (Group Detroit) on Saturday, December 5, 2015. I spoke to the officer on duty and explained the discrepancy I was seeing between the AIS AtoN position and the usual position for the aid. He said he would pass on this information to the appropriate command or sector for the AIS AtoN. The Coast Guard corrected the AIS AtoN position being transmitted by the time I checked it on the following Friday, December 11, when I made the screen capture (above) showing the buoy in its proper position. (The latitude of LB12 was being sent as 43-deg 03.466-min N; the corrected position is now being sent as 43-deg 05.466-min N. The error was probably a typo when entering data into the N-AIS base station transmitter configuration for the AIS AtoN.) In a conversation I recently had with a Coast Guard official involved in AtoN work, he said they got a lot of reports about the AIS AtoN being in the wrong position.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Mon Dec 14, 2015 2:07 pm

In reviewing the screen captures I show above, there may be another error related to the AIS AtoN. Almost all the AIS AtoN types are shown as "Fixed (13)" or "Fixed (14)." The particular AIS AtoNs I have shown (above) are related to the position of floating buoys. My initial reaction is that the AIS AtoN type ought to reflect a floating aid, so the type designation perhaps should reflect that, and thus be listed as "Floating (24)" or "Floating (25)".

On the other hand, perhaps the type description of the AIS AtoN refers to where the signal originates. Since none of these AIS signals are from Real AtoNs, where the signal would originate from a floating location, but rather are all for Synthetic or Virtual AtoNs, where the signal originates from a fixed location, the AIS Base Station making the actual transmission of the signals, the description of them as "fixed" may be more appropriate. I have asked the local District 9 Coast Guard specialist in Aids to Navigation to comment about the type designators being used.

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Sun Dec 16, 2018 5:37 pm

UPDATE: now about three years after I initially wrote this article, I happened to again investigate the AIS AtoN signals being send during the Winter navigation season on the Great Lakes, or in particular, on Lake Erie. I found AIS AtoN icons that were new and different from the ones used in 2015. Since there has been no update to the firmware in my chart plotter--still the rather old HDS-8 first generation--I must assume that the icons were already available in the chart plotter. The cause for the chart plotter to display different icons than before must be due to the AIS AtoN sending a different identification type. Here is a segment of a screen capture showing an AIS AtoN icon:

unusualAIS_AtoN_Icon.png
Fig. 1. Screen capture from HDS-8 of an AIS AtoN icon. The view is North-up, so the position of the AIS AtoN is on the West side of the channel.
unusualAIS_AtoN_Icon.png (4.25 KiB) Viewed 1922 times

closeUpIcon.png
Fig. 2. Icon enlarged for better interpretation; the symbol appears to be two opposing arrowheads.
closeUpIcon.png (5.15 KiB) Viewed 1903 times

Image
Fig. 3. Recommended symbols for AIS AtoN targets.

Comparing the icon shown by the HDS-8 with the symbols in the recommended list of icons, the interpretation of the icon meaning appears to be most similar to the icon table listing for "West cardinal mark," as that is the symbol that has opposing arrowheads. In the USA, buoys or aids to navigation mark the sides of a channel in a lateral system. In contrast, cardinal marks indicate the direction of safety as a cardinal or compass direction, that is, North, East, South, or West, relative to the mark. If the AIS AtoN icon is interpreted as a West cardinal mark, it would be suggesting that the deeper water was to the West of the mark. This is actually true. The chart presentation, in this particular instance as seen in the screen capture, is inaccurate.
[Article continues below.)

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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Mon Dec 17, 2018 10:56 am

On the HDS-8 the screen also for viewing the "AIS Info" or supplemental information about the target.

AIS_Info.png
Fig. 3. AIS Info data from HDS-8. Note the value for TYPE.
AIS_Info.png (16.64 KiB) Viewed 1895 times

The AIS Info page indicates that the AIS AtoN is a type "Fixed (13)." To interpret this meaning we must consult another listing of AIS Message data, so we turn to the USCG NavCen website. There we can find a very informative webpage with a description of a large number of messages associated with AIS AtoN targets.

In the list we find that Field-4 of AIS Message type 21, AIS AIDS TO NAVIGATION (ATON) REPORT, contains a numerical value for the type of aid. This numerical value is then interpreted by consulting a list from the International Association of Lighthouse Authorities (IALA), shown below. We then search the list to see what description is provided for a type value of 13.

AIS_AtoN_List.png
Fig. 4. List of types of AIS AtoN from IALA.
AIS_AtoN_List.png (24.79 KiB) Viewed 1895 times

Consulting the above list for the meaning of a numerical value of 13 in the AIS Message 21 Field-4 value, we see the interpretation is "Beacon, Port Hand." This is a really confusing result. The aid is described as a fixed aid, as distinct from a floating aid, and the indication is "Port Hand."

Inasmuch as I am not familiar with navigation aids of "Port Hand" type, I had to search for more information. The interpretation of "Port Hand" means a mark that will appear on the port side of a vessel that is traveling in the channel in the direction of the buoyage. (This is explained more thoroughly in another post, below.) Since there are two IALA regions, the interpretation for Region B (the Americas) is to be used, so a Port Hand mark is a GREEN mark.

I then loaded the chartplotter with a better chart for this area. and then I could also get data about the aid to navigation from the chart data using the HDS-9 (CHART) INFO option in the MENU option list.
HDS_Chart_InfoScreenCapture.png
Fig. 5. Chart Info screen from HDS-9
HDS_Chart_InfoScreenCapture.png (13.7 KiB) Viewed 1895 times


As the above information screen shows, the AIS AtoN is to be interpreted as a green or port-hand mark. This makes the use of the icon for a cardinal mark rather conflicting with the actual meaning.

jimh
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Wed Dec 19, 2018 2:33 pm

Another UPDATE:

After more testing with my HDS-8 and AIS AtoN signals, I have found the outcomes to be variable, that is, the representation of the AIS AtoN with an icon having opposing arrowheads is not consistently repeatable. Below I show the results of another test.

To better find AIS AtoN icons, I zoom-out on the chart display screen so that most chart details drop out. This leaves just the AIS icons overlaid, and they become very easy to see. Figure 1 below shows this:

Fig1.png
Fig. 1. HDS chart screen showing AIS AtoN icons.
Fig1.png (6 KiB) Viewed 1854 times


The AIS AtoN target that we will examine is the one just to the upper-left of the crosshairs. Note that this icon is showing the standard default target icon, a rhombus with a cross inside. Next we zoom in on the chart to get a better look.

Fig2.png
Fig. 2. The AIS AtoN with chart zoomed in to show details.
Fig2.png (3.55 KiB) Viewed 1854 times


By zooming in we see that the AIS AtoN target is marking the side of a fairway or channel. It is close to a physical mark, but its electronic position is slightly different than the physical mark. This is handy for this presentation, because the AIS AtoN icon does not land atop the chart icon for the actual aid to navigation, and we can see the icon very clearly.

As mentioned earlier, the HDS chart plotter can reveal more information about an AIS target by positioning the cursor over the AIS icon, hitting the MENU button, and selecting the choice AIS INFO. When that is done, the AIS INFO screen appears, giving more data about the target. This is shown below.

Fig3.png
Fig. 3. AIS INFO screen for the AIS AtoN under discussion.
Fig3.png (15.95 KiB) Viewed 1854 times


The AIS INFO screen gives the MMSI of the AtoN and its "type." In this example, the type is "Fixed (14)." Again consulting the IALA list of designations and meanings, we get the interpretation: "Beacon, Starboard Hand."

While I again find that description a bit confusing, and I would prefer a simple notation of red or green, there is a reason for this apparent obscurity: in the IALA there are two sets of plans or schemes for lateral buoyage, and the colors red and green mean exactly the opposite in those two schemes. But the term "Starboard Hand" means the same. An aid to navigation described as "Starboard Hand" marks the edge of the channel on the Starboard side of a vessel that is travelling in the direction of the buoyage system. Of course, this adds another obscure term, "the direction of the buoyage." The simplest definition may be that the direction of the buoyage corresponds to the direction in which the numbering of the aids is increasing. In most instances, the direction of the buoyage thus corresponds to going upstream in a river system or to entering a port from the sea.

Now that we understand--and I hope I made it clear--what exactly a "Starboard Hand" mark will be, we have to figure out which IALA system is in use. For North America, all buoyage has been conformed to use IALA REGION B. So now we can finally figure out what electronic color the AIS AtoN represents: a Starboard Hand mark will be a RED mark in the USA.

As for the description "Fixed", I can only infer that because there is not an actual floating navigation buoy at that position, this is a virtual AIS AtoN, and its position is thus fixed, that is, the position is not going to change due to some drift by a buoy with wind and current. (For the definition of a virtual AIS AtoN, see the follow-on article below.)

For comparison to the real aid to navigation close to the AIS AtoN, I also got information from the electronic chart publisher using the chart plotter. Again, the cursor is moved over the icon, this time for the real AtoN, and an information screen pops up:

Fig4.png
Fig. 4. INFO screen for the adjacent actual aid to navigation.
Fig4.png (8.08 KiB) Viewed 1854 times


Now we see that the actual physical aid close by is a RED mark. This makes the AIS description very appropriate. Also note that this screen reveals the buoy number, "8", and this explains why in the earlier (Fig. 3) illustration the AIS INFO screen had the number "8" in its upper banner: it's the number of the electronic aid, too.

This example contradicts my earlier example in which the AIS AtoN icon seemed to appear as a set of opposing arrowheads. I believe I have found the reason for that unusual presentation: there is some interaction of the graphics display in which the icon element and the dashed line element representing the channel edge land in a particularly unfavorable way, resulting in the icon for the AIS target and the chart dashed line combining to change the appearance. I will demonstrate below with two more illustrations.

First we see a normal AIS AtoN icon, close to a dashed line element, as occurred above in our chart display in Fig. 2.
Fig5.png
Fig. 5. An AIS AtoN icon with normal crosshair and a channel edge dashed line element.
Fig5.png (511 Bytes) Viewed 1854 times


What if, by chance, the AIS AtoN icon happened to be exactly on the dashed line of the channel boundary, as might often be the case? The two elements could combine graphically, and produce a display that looked like this:

Fig6.png
Fig. 6. Display resulting from AIS AtoN icon overlaying chart dashed line.
Fig6.png (554 Bytes) Viewed 1854 times


The resulting display resembles the sort of strange icon observed in my earlier update, in which the icon appears to contain opposing arrowheads. I now believe that this random alignment of the chart elements may have produced the unusual icon presentation for the AIS AtoN as a cardinal mark, when it was much more plausible that the AIS AtoN was a lateral mark.

jimh
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Wed Dec 19, 2018 3:31 pm

A reminder:

AIS Real AtoN means there is an actual physical aid and there is an AIS transmitter at that aid.

AIS Synthetic AtoN means there is an actual physical aid but the AIS transmitter is on shore and just sends out the position of the physical aid.

AIS Virtual AtoN means there is NO actual physical aid, and the AIS transmitter is on shore and sends of the position of the nonexistent physical aid

jimh
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Re: Display of AIS AtoN on Lowrance HDS-8

Postby jimh » Thu Dec 20, 2018 10:14 am

The ability of the HDS-8 to display AIS AtoN targets can be summarized as follows:

  • for a legacy device, the HDS-8 does a good job of displaying AIS AtoN targets, considering the age of the firmware the chart plotter is running on
  • the icon used for all AIS AtoN targets is the generic icon
  • there are no distinguishing elements in the screen chart display to differentiate virtual aids from physical aids, which could be confusing to a mariner looking for a physical aid to navigation to appear as he pilots this vessel in a channel
  • there are no distinguishing elements in the screen chart display to indicate Port or Starboard hand marks
  • at some zoom levels the appearance of the icon for an AIS AtoN seems to morph into something other than the basic rhombus with internal cross, perhaps causing confusion.