turn direction: using azimuth

in using azimuth to determine turn direction, i...

select azimuth or reverse azimuth of segment depending on heading of observer

subtract target's azimuth from source's azimuth

if the difference falls on the right side of the quadrant it's a LEFT turn
difference ( < 0 and > -180 ) or ( > 0 and > 180 )

if the difference falls on the left side of the quadrant it's a RIGHT turn
difference ( < 0 and < -180 ) or ( > 0 and < 180 )

i also consider an acute angle buffer to consider angled segments' connection as segment change rather than as a turn
i use +-25