Definition of Hoirzontal Annotation

Question

User enquired how are the values of DOC and Delta angle from Geometry > Horizontal Annotation for the horizontal alignment? Any equation or graphic can show what is the definition of the value ? 
 InRoads: 08.11.07.615

caddcop · Accepted Answer

Delta is the internal angle between PC, Center of Curve and PT, which also is equal to the deflection angle - angle turned at PI, when the starting angle (zero measurement) is looking along the back tangent direction but away from the PC and the ending angle is looking along the ahead tangent towards the PT. 
 The Degree of Curve is the angle that a 100' arc, measured along the curve, would be turned. 
 BTW, generally, highways use the 100' arc while railroads use a 100' chord. There is a place to select arc or chord definition for degree of curve in InRoads Options. 
 Generally, as I understand it, the Degree of Curve is not used when using metric units.