From Wikipedia, I learned that an affine transformation between two vector spaces is a linear mapping followed by a translation.
But in a book Multiple view geometry in computer vision by Hartley and Zisserman:
An affine transformation (or more simply an affinity) is a non-singular linear transformation followed by a translation.
I wonder if these are two different concepts, given that one does not require the linear transformation to be non-singular while the other does?
Thanks!