From PI to 1/4 points on curve
Given:
D, select R, then find 1/4 point and midpoint on curve from PIA quick method to fit curve to ground conditions where the defl.-angle is not too large and the PI is easily accessible
tan
a = [(1 - cosD/4)(cosD/4)] / sinD/4[1 + (1 - cosD/4)(2cosD/4)]pg 93 Hickerson
r = y /sin
a = R*versD/4/ sina (special case of 1/4 points