Meeting Points (Only SEAiq Pilot)

When an AIS target is following the same route, it can be useful to estimate where they may meet along the route. This is called their Meeting Point.

If traveling opposite directions, the meeting point is where the two vessels pass each other. When the vessels are in the same direction the vessel behind is overtaking the vessel in front, the meeting point is the location where they are overtaken.

This feature is commonly used when navigating rivers and similar confined channels, where the vessels can be expected to follow the course of the river. SEAiq will estimate the time until they meet and the approximate point of meeting along the route. The meeting point is displayed as a magenta circle along with the name of the target.

The AIS tab has an option called Route Traffic for organizing targets on your current route along with their meeting points.

Conditions for Meeting Point

IMPORTANT: the meeting point estimate uses a number of assumptions, such as that the vessels are actually following the same route, they maintain current speed, etc. The estimate is only accurate to the degree that the assumptions hold. In the case of vessels with similar speeds overtaking each other, the estimate may have a significant amount of error.

The following conditions must be met for a meeting point to be displayed:

• Own-Ship must be following a route.
• The target must be moving at least 1kn.
• Both vessels must be within a maximum distance from the route. The default maximum is 1nm, but this can be adjusted in the settings below.
• Each vessel must be within 25 degrees of the direction of the route segment it is on.
• To be displayed on the chart, the meeting point must be a minimum range from Own-Ship. This is done to avoid clutter. The default minimum range is 0.25NM.
• The meeting point must be somewhere along the route.

You can see the time to meeting by pulling up the AIS record. The current status is displayed under "Route Meeting Point." If there is no meeting point, the status given will help you understand why not. The possible status values for meeting point are:

• Vessels meet in time
• Own-Ship overtakes Target in time
• Target overtakes Own-Ship in time
• Vessels moving apart
• Own-Ship pulling away from Target
• Target pulling away from Own-Ship
• Own-Ship/Target not on route
• Speed for Target below 1kn threshold
• No position for Target/Own-Ship
• No course for Target/Own-Ship
• No speed for Target/Own-Ship
• Vessels meet past end of route

Manipulating Meeting Points

You can select a meeting point and drag it to a new location along the route. As the meeting point is moved, the required change in speed to move the meeting point is shown. A speed is given both for Own-Ship and the target. If either vessel (but not both) were to change their speed to what is shown, then the meeting point would change to the location. If the required new speed for one of the vessels would be greater than 35kn then that speed will not be shown.

Alternatively, you can select a vessel and drag it along the route. As you do this, both Own-Ship and the target will be moved so that their positions correspond to where they would be at a given time. If the new position of the target is where it is estimated to be after 5 min, then the Own-Ship position will also be estimated for 5 minutes.

Settings

• Show Meeting Points (Only SEAiq Pilot) : This enables display of Meeting Points for AIS targets.
• Show Lines for Meeting Points (Only SEAiq Pilot) : When enabled, lines are shown at meeting points perpendicular to the route. This only applies to vessels larger than Small Vessel Length.
• Distance Threshold (Only SEAiq Pilot) : This is the maximum distance Own-Ship or an AIS target may be from the current route and still be considered to be following the route. Further conditions for a vessel to be considered following a route are in the Meeting Point overview.
• Small Vessel Length (Only SEAiq Pilot) : AIS targets less than this length are treated differently. They have meeting points shown with green Meeting Point symbols. This can be used to identify smaller vessels. See other settings for other effects.

Display Filters

• Only Show Selected AIS Target (Only SEAiq Pilot) : When enabled, only show the meeting point for the currently selected AIS target.
• Minimum Range (Only SEAiq Pilot) : Only display the meeting points that are at least this far from Own-Ship. This can help in reducing clutter and distractions around Own-Ship. The default minimum range is 0.25NM
• Ignore Small Vessels (Only SEAiq Pilot) : When enabled, meeting points for small vessels are not shown.

Alarms

• Meeting Point Alarm (Only SEAiq Pilot) : Alarm fires when new vessels appear on your route with a meeting point.
• Passing Restriction Alarm (Only SEAiq Pilot) : Alarm when a meeting point is detected along active route segment where passing is restricted. This only applies to vessels larger than Small Vessel Length.

Cross-Route Meeting Points

• Enable Cross-Route (Only SEAiq Pilot) : When enabled, cross-route distances are displayed. This function does not require that same-route meeting points be enabled. For any vessel at most one type of meeting point will be identified. If types of meeting points are enabled, then targets with a known route will use cross-route meeting points and other vessels will use same-route meeting points: cross-route meeting points are given preference.

• Threshold Distance (Only SEAiq Pilot) : Distance threshold used to consider when two vessels are approaching. A cross-route meeting point will be identified only if two vessels approach within this distance at some particular time. The default value for this is 1NM.

  Important: a large threshold value can cause confusing results. Be sure to use the smallest threshold value for meeting points that you are interested in learning about.

Cross-Route Meeting Points

Meeting points can also be found in situations where the other vessel is following another route that crosses or approaches Own-Ships route. We call the Cross-Route Meeting points MPX's. MPX's are shown with an X in them.

Similar with single-path meeting points, MPX assume both vessels will exactly follow their current routes.

There are 2 types of MPX that may be shown. These are called First Point of Approach (FPA) and Closest Point of Approach (CPA). The FPA is shown for situations where the two vessels approach each other close enough to require warning the mariner, but later have a closer approach. In these cases, information about both the FPA and CPA is shown. The MPX Threshold Distance is used to determine the maximum distance at which an approach will be considered for FPA.

Goal Point

You can select the FPA meeting point and then slide it to determine what speed change is required to change the meeting point. These calculations are updated continuously as the position moves. The steps used to calculate changes to the meeting point are as follows.

1. The closest point to either Own-Ship or Target route is located.
2. The closest point from the point in (1) is found on the other route.
3. The two points are considered the Goal Points for each of Own-Ship and the Target.
4. The time required for Own-Ship to reach its Goal Point at its current speed is calculated. This is the Goal Time.
5. The speed required for the Target to reach its Goal Point at the Goal Time is calculated.
6. If the required speed is at least 30kn the speed is labeled High.
7. The same calculation in 4-6 is made again, but with roles of Own-Ship and Target reversed. The Goal Time for the target is calculated and then the required speed for Own-Ship.

Target Advance

It is also possible to select the Target vessel and slide it on its route. The time for the Target to reach that point is calculated and then point the Own-Ship would be at the same time is shown, along with the distance between the two vessels. This can be used to see how the two vessels will approach each other.