The FROC Routine is similar to the FROS Routine, except that points are established on a curved frontage.
Only one frontage line may be handled with a FROC heading, however any number of points may be established on that frontage line.
The known starting point on the curved frontage is entered under known point, course A, and the centre of the
curve under known point, course B. The required point is entered under the unknown point heading and the
distance, or angular deflection, from the known point in course A. The type of distance or rotation of
angular deflection is determined by the code column of course A, viz:
If a distance is given, A indicates arc length, C indicates chord length. Note if a +ve distance is given,
clockwise rotation is assumed, and anticlockwise for -ve distance.
If an angle is given, a code of A indicates anticlockwise rotation, a code of C indicates clockwise rotation.
Each subsequent entry under the same FROC heading defines another point on that frontage line.
In such cases the required point is entered under unknown point and the distance, or angular deflection,
from the last established point, in course A. The same facility for computing multiple points in FROS may be used with FROC.
An example of FROC is shown below. The first example defines points 131 through 135 around centre point 130
from point 129 using arc distances. The second example uses a chord distance to define point 247 and an angle to define point 248
XY Data Point Record Col
Record Type 02 1
Routine FROC 2
Unknown Point ____ 3
Course A - Known Point ____ 4
Bearing _______ 5
Code (P) _ 6
Distance __________ 7
Indicator _ 8
Point 1 ____ 9
Point 2 ____ 10
Course B - Known Point ____ 11
Bearing _______ 12
Code (P) _ 13
Distance __________ 14
Indicator _ 15
Point 1 ____ 16
Point 2 ____ 17
Auxiliary Point ____ 18