Using Eigen::Vector3f in OpenMesh mesh

EigenOpenMeshPlugin.h

EIGEN_STRONG_INLINE Matrix &normalize() {
  *this /= norm();
  return *this;
}

EIGEN_STRONG_INLINE Scalar length() const { return norm(); }

EIGEN_STRONG_INLINE Matrix &vectorize(Scalar v) {
  fill(v);
  return *this;
}

OpenMesh.h

#define EIGEN_MATRIX_PLUGIN "EigenOpenMeshPlugin.h"

#include <Eigen/Core>
#include <Eigen/Geometry>
#include <OpenMesh/Core/Mesh/Traits.hh>
#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>

namespace OpenMesh {
template <typename _Scalar, int _Rows, int _Cols, int _Options>
struct vector_traits<Eigen::Matrix<_Scalar, _Rows, _Cols, _Options>> {
  static_assert(_Rows != Eigen::Dynamic && _Cols != Eigen::Dynamic,
                "Should not use dynamic vectors.");
  static_assert(_Rows == 1 || _Cols == 1, "Should not use matrices.");

  using vector_type = Eigen::Matrix<_Scalar, _Rows, _Cols, _Options>;
  using value_type = _Scalar;
  static const size_t size_ = _Rows * _Cols;
  static size_t size() { return size_; }
};

template <typename _Scalar, int _Rows, int _Cols, int _Options>
struct VectorDimensionsT<Eigen::Matrix<_Scalar, _Rows, _Cols, _Options>> {
  static_assert(_Rows != Eigen::Dynamic && _Cols != Eigen::Dynamic,
                "Should not use dynamic vectors.");
  static_assert(_Rows == 1 || _Cols == 1, "Should not use matrices.");
  enum { value = _Rows * _Cols };
};

template <typename Derived>
typename Derived::Scalar dot(Eigen::MatrixBase<Derived> const &v1,
                             Eigen::MatrixBase<Derived> const &v2) {
  return v1.dot(v2);
}

template <typename Derived>
typename Derived::template cross_product_return_type<Derived>::type
cross(Eigen::MatrixBase<Derived> const &v1,
      Eigen::MatrixBase<Derived> const &v2) {
  return v1.cross(v2);
}
}

You may also need to force OpenMesh to use right alignment for points and normals:

#include<Eigen/StdVector>
EIGEN_DEFINE_STL_VECTOR_SPECIALIZATION(Eigen::Vector3f); // Type used in traits.

Though in MSVC it may not be required because it auto aligns in 64 bit builds.