Setting eigen “Transformation” class as column major for post/right multiplication

Question

I have a function that does a lot of post/right multiplication of transformation matrixes .Now I want to convert this function to use Eigen and the problem is Eigen Transformation class does the multiplications as pre/left multiplication. Which means it has row matrix format during multiplication While storage is in column matrix format.

is there a way to change Eigen::Transformation class members from row major to column major?

Answer 1

The full signature for the Eigen Matrix class is

Matrix<typename Scalar,
       int RowsAtCompileTime,
       int ColsAtCompileTime,
       int Options = 0,
       int MaxRowsAtCompileTime = RowsAtCompileTime,
       int MaxColsAtCompileTime = ColsAtCompileTime>

The 4th argument Options is described as

Options is a bit field. Here, we discuss only one bit: RowMajor . It specifies that the matrices of this type use row-major storage order ; by default, the storage order is column-major. See the page on storage orders. For example, this type means row-major 3x3 matrices

So you could say, for example,

Matrix<int, 3, 4, ColMajor> foo;    // column major
Matrix<int, 4, 3, RowMajor> bar;    // row major

More documentation on Storage Orders

If the transformation you are referring to is Eigen::Transform this also has an Options template argument, which you can also pass RowMajor vs ColMajor . Any matrices it produces will follow the same convention that you specify.

Transform<typename Scalar,
          int Dim,
          int Mode,
          int _Options = AutoAlign>

Again the _Options argument is described as

_Options has the same meaning as in class Matrix . It allows to specify DontAlign and/or RowMajor . These Options are passed directly to the underlying matrix type .