What is the eigen way of converting vector3d to vector3i or vector2i.
Eg. how do i convert vector3d vec(3.555,0.4444,3.333) to vector3i and vector2i?

This code casted your example double vector to an integer vector for me:

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    Eigen::Vector3d vec(3.555,0.4444,3.333);
    Eigen::Vector3i i_vec = vec.cast <int> ();
    std::cout << i_vec;

Source: https://stackoverflow.com/a/53497636/13784831

This code "selects" the first 2 elements in the vector:

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    Eigen::Vector2d vec_2 = vec.block(0, 0, 2, 1);
    std::cout << vec_2;

Reference: https://eigen.tuxfamily.org/dox/group__ ... tions.html

Combine these to convert the first two elements of a double vector to a 2-element integer vector:

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    Eigen::Vector2i i_vec_2 = vec.block(0, 0, 2, 1).cast <int> ();
    std::cout << i_vec_2;