factor
The factor grows from -1 to 0 to 1. The slope depend on the start and end parameters of the class.
relativeDistance < -end -> -1f
relativeDistance in -end..-start -> -1f..0f
relativeDistance in -start..start -> 0f
relativeDistance in start..end -> 0f..1f
relativeDistance > end -> 1f
if abs(relativeDistance) in start..end
the factor changes linear.