Eigen combine rotation and translation into one matrix

Question

I have a rotation matrix rot (Eigen::Matrix3d) and a translation vector transl (Eigen::Vector3d) and I want them both together in a 4x4 transformation

Answer 1

Another method is to do the following:

Eigen::Matrix3d R;
// Find your Rotation Matrix
Eigen::Vector3d T;
// Find your translation Vector
Eigen::Matrix4d Trans; // Your Transformation Matrix
Trans.setIdentity();   // Set to Identity to make bottom row of Matrix 0,0,0,1
Trans.block<3,3>(0,0) = R;
Trans.block<3,1>(0,3) = T;

This method literally copies the Rotation matrix into the first 3 rows and columns and the translation vector to the 4th column. Then sets the bottom right matrix entry to 1. You final matrix will look like:

R R R T
R R R T
R R R T
0 0 0 1

where R are the corresponding values from the rotation matrix and T the values from the Translation vector.