- OpenCPN User Manual
- Getting Started
- Basic Features
- Advanced Features
- License and Authors
For a general introduction to AIS, Wikipedia is a good place to start.
The screen-dump below gives you a first feel for how AIS targets are presented and used in OpenCPN.
The Lookahead mode is activated here and our own vessel is proceeding 352 deg at 13.8 kts, leaving an activated track behind, and projecting a dashed line ahead representing the course. This ends in a dot, that represents where we will be in 6 minutes, or 1.38 nautical miles ahead. We are meeting a vessel, steaming in the opposite direction following the traffic separation. This target also has a line and a dot in-front of it representing course and where it will be in 6 minutes(user configurable), and a track behind it.. The two blue dots with a red/yellow line between them, represents where the vessels will be at CPA - closest point of approach, or when the are nearest each other, with present courses and speeds. The meeting vessel is red, as it is a potential danger to us. An AIS target alert dialog has just popped up.
There is a lot of information about the vessels that transmits AIS signals.
The cursor is on top of the the meeting vessel on a SW course. As we have not yet received full information, this can take a while, we don't get the name but an id number, the so called MMSI number, instead. Exactly what is shown in the yellow pop-up is configured in the AIS tabs Rollover heading.
This vessel is identified by name, and has a green color, as it does not represent any danger to our navigation.
If we instead of just hovering the cursor on an object, double click it, the dialog above pops up. A lot of relevant information is displayed. CPA, "Closest Point of Approach", to ownship is 9.1 miles in 8h 16min.
More information about the target itself, is available on Internet address: http://www.marinetraffic.com/ais/shipdetails.aspx?mmsi="MMSI number here", in this case: http://www.marinetraffic.com/ais/shipdetails.aspx?mmsi=233150000
Create Waypoint drops a mark at the targets current position.
Right-clicking a target brings up a dialog focused on AIS.
Aids to Navigation AtoN
More and more aids to navigation are equipped with an ais transmitter, and shows up as a target in OpenCPN like this
Note the word "Real", that says that this is an object that exists in reality.
Here we have an AIS transmitter on a floating W Cardinal Mark.
This is of course real and the buoy is on position. If the buoy is off position, for some reason, the Aton icon becomes red.
There are also Virtual AtoNs marked with their own icon .
Virtual AtoNs are used to quickly make mariners aware of things like new wrecks, uncharted hazards and floating debris. They are normally used for a short duration until replaced by real buoy, charted, removed or dispersed.
Virtual AtoNs are also used for information. An example...the position of the Italian Maritime Rescue Coordinating Center. Note the word "Virtual" in the dialog.
|OpenCPN handles the situation where MMSI is set to 0 (zero). This can occur with an incorrectly configured Aton. Nevertheless, all available information is shown.|
The AIS Target List
Another way to present the AIS information. The AIS target list is available through the right click menu. Click on the header in a column to sort according to this criteria. For example, clicking "Range" sorts the targets with the nearest target on top. Click one more time to get the target, furthest away on top. Sorting works as described only if there is a maximum of 1000 targets. Sorting does not work at all with more targets.
Active Search And Rescue Target (SART) and Digital Selective Calling (DSC) distress targets, will always stay at the top of the list, even when sorting.
AIS targets with Lat > +/-85 deg will show brg "unavailable". OpenCPN is not suited for Polar Navigation.
Target Info button: Click on a target to highlight it and then click the button to display the information dialog.
Center View button: Highlight a target an click this button and the screen will center on the target.
Limit Range: The list will only show targets with a range less than, or equal to this value.
Target Count: Total number of AIS targets.
AIS Transponder and Ownship.
OpenCPN 3.2 does not show the ownship (i.e. AIVDO message) neither as an AIS target, nor in the target list. AIVDO is processed only in the main navigation thread.
Earlier releases did show ownship, but this was a bug, simply an illusion.
The earlier presence of AIVDO (ownship) information in the data stream, really only indicated that the transponder was turned on and received GPS signals. The only true way to monitor the output of a transponder, is with a separate AIS receiver.
AIS data port
Select your AIS input port in the Connection Tab. The AIS button in the ToolBar, appears different according to the following conditions.
AIS Alive. The default AIS button. This icon appears as soon as an AIS port is active in the tool-box. It is also the normal state with an AIS receiver working and with no targets of interest.
AIS Alive and Activity, a small green circle will illuminate in the lower right corner of the Ais buton. If there is at least one AIS message every 4 seconds, the light will remain illuminated.
AIS Suppressed. This icon indicates only that target suppression is activated in the AIS tab in the ToolBox. Referring to the picture above there are two sort of suppression:
* Suppress display of all moored/anchored targets, max speed specified in dialog.
* Suppress Alerts for moored/anchored targets.
This icon will be over-ridden with the AIS alarm button if an alarm is, or becomes, active according to the AIS tab alarms settings in the toolbox.
AIS Alarm. A target exist that raises the alarm as defined in the AIS tab in the ToolBox. It is the three settings "CPA Calculations", that rules if and when an alarm is raised.
AIS Disabled. No targets, if available, are shown on the screen. This button toggles with the other buttons. For example, if the AIS alarm button is visible, click the button and it will change to the "AIS Disabled" button, and all targets, alarms etc, disappears from the display. Click again and the original button and AIS display comes back.
The ToolBox AIS Tab
This tab controls the behaviour of many thing in the AIS display. There are no "best" settings. It all depend on where you are, what kind of navigation you are into and what kind of vessel you are on. It is your responsibility to evaluate this.
CPA calculation: Rules for when the Closest Point of Approach- CPA (when two vessels are nearest each other) and the Time For Closest Point of Approach (TCPA) is calculated, and when warnings are activated.
There are three tick boxes, which can be activated with user set values.
No CPA Calculation if target range is greater than (NMi)
If the vessel is far away it is less interesting to calculate CPA. In a busy waterway this could cut down on clutter and processing speed if a reasonable value is set.
Warn if CPA is less than(NMI)
Similar arguments to No 1. This controls when a warning for minimum CPA distance is given. A warning can be both on the screen and a sound. The CPA is shown on the screen when a warning is active.
..and TCPA is less than (min)
This Box can only be activated if the previous box is active. If the minimum CPA is far in the future, it's not so interesting. If it's hours away, both vessels have probably changed speed and course in the meantime. Set TCPA to a reasonable value value depending on circumstances. A lower value if negotiating a busy waterway. A higher value when offshore. Many factors plays a role here. If you need to get off watch crew up on deck for a manoeuvre, take this into account, for example. Do you find that you get to many useless alarms? Consider lowering this value and/or the CPA value.
If a target is within the distance set in #1 and without an active warning, theCPA can be shown anyway through right-clicking on the target.
"Show Target CPA" toggles with "Hide Target CPA"
More About Target CPA, a few more tricks are available.
Lost Targets: Rules for how lost targets should be handled on the display.
Mark Target as los after (min)
Target is regarded as lost if no transmission are received for the number of minutes set here, the target will change on the display and have a black bar across.
Remove lost targets after (min)
The lost target will be removed from the display after the number of minutes set here.
Display: If and how a vessels course and speed should be displayed and if stationary vessels should be on the screen.
Show target COG predictor arrow, length (min)
An arrow will be shown in front of the vessel representing it's COG (Course Over Ground). The length of this arrow and the dot at the end of it represents the calculated position in the number of minutes set here. Set easily calculated values. If a vessel approaches you doing 15 kts and the time is set to 6 minutes, the dot will be 1.5 nautical miles ahead of the vessel.
|The width of the "Target COG predictor arrow" can be adjusted in the opencpn.ini configuration file. Find the line below and adjust the value.
Warning: Don't edit to the opencpn.ini (opencpn.conf) file when OpenCPN is running.
Show target tracks, length (min)
A track will be shown behind a target. This helps to judge the target vessels intentions.
When this option is ticked, the context sensitive AIS menu changes to include the toggle option "Hide Target Track" / "Show Target Track".
Hide anchored/moored targets, speed max (kn)
A target will not be displayed if the speed is less than the value set here. There are two exceptions to this rule, Aids to Navigation (Aton) and "Vessels Not Under Command". The rule is aimed at catching anchored or moored vessels. The "Navigational Staus" is set by the ships and may not be correct.
Be aware that the COG arrow will not be shown for any target with a COG less than this value, hence it's important to enter a very low value.
Show Area Notices(from AIS binary messages). More about AIS Area Messages here.
Show AIS targets real size. Zooming in on a target will eventually show a rectangle using the real size , if available. The picture below also shows how differences in course and heading are treated.
Show names with AIS targets at scale greater than 1:[select value]
With this box activated.....this is what you get!
Treat WPL sentences as APRS position reports.
APRS (Automatic Packet Reporting System) is utilized by HAM radio operators around the world.The NMEA WPL sentence is shorthand for for "waypoint location". If this box is ticked, a WPL sentence will be assumed to be an AIS-like APRS target.
Rollover: Tick the boxes for the kind of information shown when hovering with the cursor over a target. This is what you get with all the settings ticked.
CPA/TCPA Alerts and DSC/SART Emergencies: When an alert is triggered, a jagged circle in red is drawn around the target that set off the alarm. Additional events can be set here, drawing more attention to the alarm. For practical navigation, make sure your alarm sound is set.
Show CPA/TCPA Alert Dialog
Shows an alert dialog on the screen with target information when an alarm is triggered. This setting only applies to AIS CPA/TCPA alerts. A DSC/SART emergency will always generate a dialog.
Play Sound on CPA/TCPA Alert Dialog and DSC/SART emergencies
Sounds an alarm when an alarm is triggered.
Supress alerts for anchored /moored targets
Don't show alarms for anchored and moored targets.
Select Alert Sound. Select an alarm that suits you, instead of the installed default sound. This alarm will also be used if an anchor watch is set. Due to copyright issues, only a few sound files are included. The default location for these files are "/usr/share/opencpn/sounds/" on Linux and typically C:\Program Files\OpenCPN\sounds on Windows XP. Users can add their own generic ".wav" sound files. These files can be in any suitable place in the file-system.
Test Alert Sound. Test the selected sound and make sure this important feature is working
Enable Target Alert Acknowledge timeout. Once a target alert is acknowledged, wait the set number of minutes before the alert comes up again (if still applicable).
When exactly is an alarm activated?
An alert is set off if your boat is approaching the CPA, the blue dot on the extension of the course line, and the previously discussed set of conditions are met. Once the distance to the CPA increases, this happens when the involved vessels has passed each other, the alarm stops, even if the other conditions still apply.
|One user noticed an alert every few seconds, yet the target was still green. The explanation is:
Variation between alert status and ship icon color is due to rapid changes in target course/speed. The target color can change from red to green while the alert dialog is showing. This may happen so fast that the red icon is not actually seen. OpenCPN does not automatically cancel the alert dialog in this case, in order to not mask information.
Types of Transponders recognized by OpenCPN
ATON Aid to Navigation, both "Virtual" and "Real".
BASE Base Station
GPSG_BUDDY GpsGate Buddy Targets
DSC Digital Selective Calling Targets
SART Search and Rescue Transponder Targets
ARPA Automatic Radar Plotting Aid Tagets
APRS Automatic Packet Reporting System Targets
Quick Reference for targets:
Note that AIS targets reporting position unavailable will be rendered in grey colour.
An active AIS SART and is a distress call equal to a "Mayday" transmission.
More about AIS SART.
Icon displayed when testing an AIS-SART device.
No Danger. Not Identified (Name not received)
No Danger. Identified
Ship which has lost fix - position unavailable. Displayed at the last known position.
Vessel not under command.
Vessel restricted in ability to manoeuvre.
Vessel constrained by draft. Vessel aground.
Vessel engaged in fishing.
High Speed- and Wing In Ground- crafts. This includes Hydrofoils, Hovercrafts and low flying crafts utilising the ground effect.
Anchored or moored. Displayed when the transmitted "Navigation status" is "at anchor" or "Moored". There is no guarantee that this status is correct, as it is set manually on the transmitting ship...
...illustrated by this ship. Note the black line on the yellow circle. This indicate that the vessel is turning to port (left), also illustrated by the lag in the display update. ROT - Rate Of Turn is available in the "Ais Target Query" dialog, through the right click menu.
The V-shape stern indicates a Class B target. Tugboats and pilot boats very often carry Class B transponders. These are often designed specifically for small commercial boats, fishing boats and pleasure crafts.
Targets is complying with the Euro AIS Inland specification.
This "Inland Blue Flag" part of the European, Inland AIS standard. "Blue Flag" signal, commonly seen on inland waters indicates that the vessel requests a "stbd-stbd" passage or crossing. This Blue Signal is manually switched on/off, by the target.
Aton, Aid to Navigation, for example a Lighthouse or a Buoy with an AIS transmitter.
Aton, Aid to Navigation, that is off it's suposed position. For example a buoy equiped with AIS that has come adrift.
Virtual Aton, Virtual Aid to Navigation, not a real marker. Can be useful for a range of situations. A new wreck, is one example. Further explanations.
Virtual Aton, off position. Actually seen in the wild, but may be a user config error.
AIS Base Statio
The following tagets only displays if DSC messages, GpsGate mesages, Radar or APRS messages are mixed in to the incomming AIS stream, by using, for example a multiplexer. More on the following pages.
DSC Station. Only the DSC message received. The position contains only degrees and minutes of Latitude and Longitude.
DSC Station. DSC and DSE messages received. The DSE message contains the missing decimals of minutes of Latitude and Longitude. The result is a much more accurate position.
DSC Station transmitting a distress signal. Treat this as a "Mayday" call.
GpsGate Buddy target.
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