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 way is to use the Eigen::Transform.

Let's take a example such as to implemente this affine transform ,

#include 
#include 
using namespace Eigen;

Matrix4f create_affine_matrix(float a, float b, float c, Vector3f trans)
{
    Transform t;
    t = Translation(trans);
    t.rotate(AngleAxis(a, Vector3f::UnitX()));
    t.rotate(AngleAxis(b, Vector3f::UnitY()));
    t.rotate(AngleAxis(c, Vector3f::UnitZ()));
    return t.matrix();
}

You can also implemented as the following

Matrix4f create_affine_matrix(float a, float b, float c, Vector3f trans)
{
    Transform t;
    t = AngleAxis(c, Vector3f::UnitZ());
    t.prerotate(AngleAxis(b, Vector3f::UnitY()));
    t.prerotate(AngleAxis(a, Vector3f::UnitX()));
    t.pretranslate(trans);
    return t.matrix();
}

The difference between the first implementation and the second is like the difference between Fix Angle and Euler Angle, you can refer to this video.