Hi David,

Direction is the same as you go north or south (or west / east). That's why the the "MainDirection" function returns only angles between 0 and 180 °.

If I understand correctly, you want to get the orientation, which can be calculated by alpha plus 180 ° (I made a little drawing to illustrate)

Here the Direction is represented by "alpha" --> A-B and A-C have the same direction. But if you want to get the orientation, A-B and A-C are not equal --> Orientation of A-C = Orientation of A-B = alpha + 180°

In version 3 ofOrbisGIS, there will be a function "azimut" which will calculate what you want.

Hope it helps you

Gwendall