CTM is the Current Transformation Matrix, which is normally a 3x3 matrix. In Postscript, it's represented as a 6 element array, since 3 of the elements in a 3x3 CTM are constant. The Postscript CTM array
[a b c d tx ty]
corresponds to the 3x3 CTM matrix
a b 0
c d 0
tx ty 1
though it's often seen in transposed form (as in the linked article):
a c tx
b d ty
0 0 1
In any case, tx
and ty
control translation and the other values combine for other transformations. Some abcd
patterns result in named transformations: rotate, scale, reflect and shear. The one you give fits the shear pattern (if we treat 0.9999999 as 1): 1 0 k 1
, where k
is the shearing amount, which is -1 in your case.