Guessing:
8.2
Kerb made up of a line of disjointed dots - lets say 5 pixels wide
9.0
Kerb made up of a smooth line maybe 50 pixels wide. Translucent at edge becoming opaque at the centre where there is a ~75%+ probability that the kerb is correctly represented at that position.
Obscured kerbs remain translucent as there is insufficient data to be confident.
Thoughts?