I do not think it is well documented, so I will try to explain it here.
Imagine we are at time point (twilight) A, particle filter simulates new positions for point B and from those for point C. After it checks
1. If AB average movement was more than 50 km
2. AB average distance was > AC.distance*1.3
3. AB.distance>AC.distance AND angle ABC<100 degrees
If this condition is satisfied it exclude point B.
I know it is not very smart filtering, so I am not a big fan of it. I will be happy if someone programmes something better, e.g. Douglas filter