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 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
- 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
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.
(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.
Only Show Selected AIS Target
(Only SEAiq Pilot) : When enabled, only show the meeting point for the currently selected AIS target.
(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.
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
(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.
(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.
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.
- The closest point to either Own-Ship or Target route is
- The closest point from the point in (1) is found on the other
- The two points are considered the Goal Points for each
of Own-Ship and the Target.
- The time required for Own-Ship to reach its Goal Point at its
current speed is calculated. This is the Goal Time.
- The speed required for the Target to reach its Goal Point at the
Goal Time is calculated.
- If the required speed is at least 30kn the speed is
- 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.
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.