those aren't affine transformations he's using, they're plane projective transformations (parallel lines aren't preserved). Yes, you can express what he means m

those aren't affine transformations he's using, they're plane projective transformations (parallel lines aren't preserved). Yes, you can express what he means more simply, but as an 8x8 matrix problem - then just use a maths library to solve it. (see eg http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/EPSRC_SSAZ/node11.html http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/EPSR...).