Alerts in NavView
Setting up Alerts in NavView is as easy as selecting a device or an observation/calculation and having it tell us if the selected item has flagged a pre-determined variable using a pre-determined logic. This is a VERY flexible tool which can use values from anything from a specific variable in a data input to an observation on a vessel or calculation.
Below are a couple examples followed by a quick rundown on how to set up an alert.
In this example we have a Vessel Heading coming in and we have a "Nominal Heading" of 157 degrees, and we want to be made aware if the heading goes +/- 2 degrees (155 degrees - 159 degrees) we can set up an alert like the below.
This can also be setup manually like below using WHEN and OR with IS ABOVE and IS BELOW
We can then view the alerts to see if they have been "Triggered". See below images, one showing the alert before trigger and then another when I set the heading to be below 155 degrees.
As you can see if the heading is outside that range for the chosen trigger the alert will be triggered
The alert will not be cleared until the heading is between 155 + <hysterisis> and 159 - <hysterisis> the hysteresis is a band around the threshold value this prevents the alert from triggering on/off continuously if you are at the limit. The threshold is used to set the alert. e.g. if the condition evaluates to true for x cycles where x is the trigger value.
For this example we are going to utilize a "Route Guidance" calculation and choose the value for the Vessel DCC and have it tell us if the value goes above 50 feet.
Setting up the alert will be like below:
And when the vessel goes above that distance it will alert us in the View Window like below:
Alert Setup and Configuration
Once Open, click the (+) to create a new alert group, and then name it as you wish, something that will help identify the alert group. Then click the (+) within the group and create the name of the individual alerts, again something so that when it goes off you know what it is..
Next is choosing the data source from the drop down that currently says "none":
You can select anything from this tree, as you can see you can choose from Calculations, Guidance, Simulations, Devices, Vehicles and more.
Once you choose your item you can choose the property, in the image below we chose the vessel position, so you can choose any of the properties associated with it.
In this example we will choose Age.
We want to set it up so that if the Age of the data coming in goes above 5 seconds it will alert us. Once you choose age, the units will auto update accordingly, so we will choose Seconds.
Once you are happy with your settings, click apply and then view your alerts.
Now WHEN the Vessel Position age is above 5 seconds this will alert red and make us aware of the issue.
Trigger and Hysteresis
The alert will not be cleared until the heading is between 155 + <hysterisis> and 159 - <hysterisis>. The hysteresis is a band around the threshold value, this prevents the alert from triggering on/on continuously if you are at the limit. The threshold is used to set the alert. e.g. if the condition evaluates to true for x cycles where x is the trigger value.
Hysteresis is used to clear the alert. The value must fall below the threshold by the hysteresis amount in order to clear the alert, in the background, the alert processor evaluates each alert every 5 seconds. So if the trigger is set to 3, that means the condition must remain true for 3 updates, or 15 seconds
The trigger can be changed from 3 to another number. A lower number will alert quicker and a higher number will take longer to alert. The hysteresis value is dependent on the property you are evaluating and a default of 1 may not be appropriate and changing to a lower number overall will have less of a buffer around your chosen triggered variable, so a value of 0 will clear the trigger almost immediately if the selected value is hit and then goes back, where as a higher number will give the data more time to swing back in case the selected variable is right on the cusp of being hit again.