SIDP routine is used to establish rear alignment boundaries when frontage points have been defined,
(or vice versa), and the allotment sides are parallel.
Only one bearing of sides may be handled under a SIDP entry, - however, the rear alignment may be
changed, and any number of points may be computed. Course B defines the rear alignment and may
be a bearing course, (giving a curved rear alignment).
Course A defines the bearing of the side boundary and the frontage point on this boundary.
On subsequent entries only the unknown point and known point in Course A need be specified,
although the rear alignment may be changed at any time by specifying the new alignment in Course B.
The same faculty exists as in SIDP and FROS for multiple point handling.
Consider the case of a front alignment created by FROS or FROC using the multiple point technique.
In such a case the front alignment would be a sequence of consecutive numbers.
The SIDP routine may then calculate a corresponding set of rear alignment points by entering the
first known frontage point, (say 220) , in the known column course A, the first unknown rear
alignment point, (say 230) , in the unknown column, and the last required rear point, (say 238) ,
in the auxiliary column. The SIDP routine would then compute a sequence of rear alignment
points 230 to 238 corresponding to the frontage point 220 to 228.
Note: In the case of SIDP for curved rear alignments, the solution adopted is that closest to
the frontage point.