I have calculated convergence index on my DEM with SAGA. Output results seems to be ok (values in range -100;100), but I don't understand how it works.
I know that Convergence Index is calculated based on aspect, therefore I've calculated Aspect in SAGA (to understand whole process), however it didn't help me. I still don't know how CI was calculated.
I've found this formula in some paper:
"Where θ denotes average angle between the aspect of adjacent cells and the direction to the central cell."
Can someone explain to me step by step how CI was calculated (for example on values inside red frame)