"Perp" is short for "perpendicular", which is the direction in which the side of the polygon is facing. Since polygons in Soldat have 3 sides, they also have 3 perpendiculars.
To calculate the perpendicular (Perp) of a polygon with vertices ordered in a clockwise order between vertex V_1 and V_2, use this code:
Diff.X = V_2.Y - V_1.Y
Diff.Y = V_2.X - V_1.X
Length = sqrt(Diff.X^2 + Diff.Y^2)
Perp.X = Diff.Y/Length
Perp.Y = Diff.X/Length
On bouncy polygons the length of the perpendicular indicates the polygon's bounce power (1 = no bounce). Calculating the perpendiculars with a bounciness factor (B) can be done like this:
Perp.X = Perp.X*B
Perp.Y = Perp.Y*B
The reason this information is saved in the map format is probably speed, but the perpendiculars could be calculated when the map is loaded in Soldat instead, so I don't really know why MM decided to make it the map editors responsibility...
