SEP tool limit

Bernardo Reis (1096507)

Controlling today, it seems that the sep tool has some kind of limit of calculation in the future.
Below is an example of what happened today in blue and what I expected to happen in magenta:

It's also worth noting that, as time went by, the SEP tool value kept changing until the value of magenta. I did not notice the time limit specifically

Juha Holopainen (839337)

Would you believe if I said this behavior, including the limit value, is stated in the plugin manual? 😉 Having the limit keeps the calculation a bit more steady (at 70 minutes I wouldn't expect the CPA solution to be very stable), and helps with performance - instead of working with spherical geometry, derivatives and such, the plugin takes the easy way and just splits the predicted path to one-minute segments and tests for CPA in each of them in order using plane geometry. Mathematically simple, but the prediction limit then has a direct impact on the number of calculations.

The limit is already adjustable using the settings, up to 999 minutes. To be more in line with the real system, in the future, when the calculation limit is reached before finding the CPA, the plugin will flag the solution as divergent, instead of displaying the smallest separation within the calculation limit.

Bernardo Reis (1096507)

Well, but in the last case you point out, they will not be divergent, correct?

And I did not remember to check the docs for this one, sorry 🫣

Juha Holopainen (839337)

As for this application the definition for convergent is "CPA within the maximum prediction time", they will be considered divergent even if in the purely mathematical sense they aren't. The limit value can then be used to define what will be presented as "converging" to the controller. Setting it to the maximum value of 999 minutes - and accepting the possible performance hit - should make it so close to the mathematical definition that the remaining difference will be operationally insignificant.

Martin Loxbo (811805)

With the risk of getting a bit philosophical about this... but isn't the SEP tool used as a tactical tool, for fairly short distances? Do you use it to assess separation between aircraft that are hundreds of miles away? Surely then there are so many variables that the result is not necessarily very accurate (changing wind and aircraft speeds).

Bernardo Reis (1096507)

I saw the 30min time limit in the manual but could not find the setting to change it.

Regarding @Martin Loxbo (811805) question, it works great for this use case: Accessing what type of action we need to do for two planes converging in the future, more or less subject to the same wind conditions, to deliver them at FCOPX according to the LoA. If speed control is enough, if nothing has to be done, or if we start accessing possibility for a level change.