SIDR routine is identical to SIDP except in that the sides are radial.
The same conditions apply, except that instead of a bearing in course A defining the parallel sides,
the centre of the radiating sides is entered in reference point 1, course A.
Note the centres of the radiating sides and the rear alignment need not be the same point.
An example of SIDR is shown below. Point 255 is defined on the radial line from centre
point 130 to point 246, at the intersection with the line joining from 256 to 253.
The next line is similar and uses the same centre point.
Note: In the case of SIDR for curved rear alignments, the solution adopted is that
closest to the frontage point.