Vessels / Meeting Points

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.

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:

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:

Settings

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Alarms

Cross-Route Meeting Points

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.