When we say "Jacobian", do we mean the matrix, or its determinant?

[N-Dekker]

itk::TransformFilter has a member function ComputeSpatialJacobianOn(), which adds the argument "-jacmat", and a member function ComputeDeterminantOfSpatialJacobianOn(), which adds the argument "-jac". So the member function names assume that the term "Jacobian" refers to its matrix, while the command-line interface assumes that "-jac" is about its determinant.

To avoid further confusion, I would prefer to always explicitly specify whether the matrix or its determinant is requested. Which is also why I proposed (with pull request #755) to add ComputeSpatialJacobianDeterminantImage() and ComputeSpatialJacobianMatrixImage().

Regarding the command-line interface, I guess we could do:

-jac mat  ---- write only the image of Jacobian matrices
-jac det  ---- write only the image of Jacobian determinants
-jac all  ---- write both images

Right?