to answer the spoiler question, i believe the circle radius needs to be greater than (equal) 1/2 the distance between two points.
This is not true. You must mean that the sum of the radii of the two points in question needs to be larger than the distance between the points.
To know what the appropriate radii are is equivalent to knowing the length of each side. TSLF never showed how he found these lengths, yet his solution depends on knowing them.
If you don't believe me, imagine trying to reconstruct a triangle using TSLF's method. Unless you know beforehand what the side lengths are, you will probably have to do a lot of trial and error to find radii that lead to a sensible reconstruction.