LightListManager User GuideAIS Targets on the Radar Display
I had not planned to include AIS targets with the LightListManager radar display, but then I discovered that the USCG broadcasts the position of a number of lights as AIS targets. The firmware on my Raymarine C120 chart plotter predates the existance of these "AtoN" targets so I was not aware of them. Once I became aware of these "real", "virtual", and "synthetic" lights I decided to include them in the radar display. Fig. 1. is a capture of the radar display zoomed out to 25 nm to show the St. John River Buoy 5 as a synthetic AIS AtoN target. A "synthetic" AtoN is an AIS target that reprsents a physical light, but the AIS data is broadcast from a tranmitter located remotely from the actual light. In Fig. 2 that transmitter is highlighted on the AIS Target Display form as MMSI 003660631, which is the base station for the Jacksonville, FL USCG. The program version that produced the screen capture used the same circular icon for AtoN targets as for stationary vessel targets. The latest version used a diamond-shaped icon for the AtoNs.
"Real" AtoN targets are broadcast from a transmitter on the physical light. A "virtual" AtoN is an AIS target that does not represent a physical light. A "virtual" AtoN might mark a shoal or obstacle until a physical navaid can be deployed or the obstacle is removed. Virtual or Synthetic AtoN targets may also document the temporary relocation of a navaid, such as during dredging operations.
The AIS implementation in LightListManager also includes vessel targets, but the program does not display these targets in accordance with the published standards.
The zoom level of Fig. 1 is well beyond any useful level for the display. Fig. 3 shows a more useful range of a little over 0.35 nm. This shows a few stationary AIS targets in the vicinity of my vessel berthed on the Ortega River. Stationary AIS targets are displayed as circles with cross inside the circle. Vessels underway are identified by an triangle with an arrow in the direction of the COG and proportional in length to the SOG. This approximates the standard depiction of AIS targets.
The AIS Target List
When "AIS Traget List" View Menu item is clicked the "AIS Target List" form is shown. Fig. 4. is a closeup capture of that form. The form provides a list of all targets that have been received and not purged. Normally a target will initially be identified by its MMSI. Once the vessel static information has been received the vessel name and call sign will be added to the entry. If no data has been received from a target for more than the Purge Time established in the View Menu, that target will be purged from the list and the icon in the radar display will be removed. If an entry in the list is selected, or a display icon is left clicked with the mouse, that target will be highlighted in the display and the list. At the end of a session (when the NMEA data input is stopped) the identitication data for all targets received during that session (including targets that have been purged) is saved. This data includes the MMSI, Ship Name, Ship Call Sign, and Ship IMO Number. The data is restored at the start of the next Radar session. This enables the saved target to be identified when the first message is received, regardless of what type of message that is. The program does not need to wait for the static information to be received before identifying a target from a previous session.
Vessel Underway Target Display
Fig. 5 shows a vessel underway in the Ortega River. I have selected this target by clicking the target icon, and the AIS Target List form shows the data that has been received on this vessel.
Center Display on AIS Target
In addition to being centered on the own ship vessel's position, the display can also be centered on any AIS target in the AIS Target List form. In Fig. 6 I have selected the "PLANE2SEA" vessel in the target list and then clicked on the "Center Target" menu item in the AIS Targets menu. Now the display is centered on this target and my vessel position is displaced from the center of the display. In the upper left corner of the display you can see that the positions shown for the vessel and the display center are now different. In this case I have selected a moving target. The display will follow that target's movement just as it follows the own ship movement when centered on the vessel's position. When the display is centered on any position other than that of the own ship, the display will be North Up and the HDG/COG vector is no longer centered on the display, but on the position of the ship.
I'm not sure if this feature has any real value. I added it more as an exercise for learning more about graphics programming than to satisfy any functional need. However, I do plan to allow the user to offset the display from the vessel postion either in this manner, or by clicking anywhere in the display or by entering a position in the Center of Display textboxes. Maybe the use for the feature will come later.