Multiplying Transform and Matrix types in Eigen

Question

To me this should just work, so the fact it does not, almost certainly means I am the one in the wrong. Even though in principle a Transform< double, 3, Affine > is the same as a Matrix< double, 4, 4 >, they cannot be used together sensibly:

Affine3d rotMat( AngleAxisd( 45.0, ( Vector3d() << 0.0, 1.0, 0.0 ).finished() ) );
Matrix4d m;
m << 1.0, 0.0, 0.0, 6.0,
     0.0, 1.0, 0.0, 6.0,
     0.0, 0.0, 1.0, 6.0,
     0.0, 0.0, 0.0, 1.0;

m = m * rotMat;

Results in a 'no match for operator=' error on the last line, and the in-place multiplication operator results in the same, trying to initialise a Matrix4d with Affine3d does not work either. Does anybody know how to actually use the Transform class in any useful way?

Thanks, Cam

Answer 1

Just write:

m = m * rotMat.matrix();

I don't know if it is an oversight that Eigen doesn't define this multiplication implicitly or if it might interfere with other use cases of the library.