xe = a0 + a1 xs + a2 ys + a3 xs ys * a4 xs xs + a5 ys ys;
(1)
ye = a6 + a7 xs + a8 ys + a9 xs ys + a10 xs xs + a11 ys ys;
where ai are the coefficients of this second order
polynomial. Each corresponding point gives 2 equations from (1), thus 18
equations are produced and an over determined linear system is obtained.
The polynomial coefficients for xe and ye
can be obtained independently, so that 2 simpler over determined systems
are solved, using a least squares method.