What kind of error do you have?
I believe this conversion operator should work fine.

on running g++ transformations.cpp 'pkg-config --cflags --libs opencv'

I get
transformations.cpp: In function ‘int main(int, char**)’: transformations.cpp:77:80: error: invalid initialization of reference of type ‘const Vec3d& {aka const cv::Vec<double, 3>&}’ from expression of type ‘cv::Point3f {aka cv::Point3_<float>}’ Affine3f cam_pose = viz::makeCameraPose(cam_pos, cam_focal_point, cam_y_dir); ^ In file included from /usr/local/include/opencv2/viz.hpp:52:0, from transformations.cpp:7: /usr/local/include/opencv2/viz/vizcore.hpp:81:29: error: in passing argument 1 of ‘cv::Affine3d cv::viz::makeCameraPose(const Vec3d&, const Vec3d&, const Vec3d&)’ CV_EXPORTS Affine3d makeCameraPose(const Vec3d& position, const Vec3d& focal_point, const Vec3d& y_dir); ^ transformations.cpp:81:132: error: invalid initialization of reference of type ‘const Vec3d& {aka const cv::Vec<double, 3>&}’ from expression of type ‘cv::Point3f {aka cv::Point3_<float>}’ Affine3f transform = viz::makeTransformToGlobal(Vec3f(0.0f,-1.0f,0.0f), Vec3f(-1.0f,0.0f,0.0f), Vec3f(0.0f,0.0f,-1.0f), cam_pos); ^ In file included from /usr/local/include/opencv2/viz.hpp:52:0, from transformations.cpp:7: /usr/local/include/opencv2/viz/vizcore.hpp:70:29: error: in passing argument 4 of ‘cv::Affine3d cv::viz::makeTransformToGlobal(const Vec3d&, const Vec3d&, const Vec3d&, const Vec3d&)’ CV_EXPORTS Affine3d makeTransformToGlobal(const Vec3d& axis_x, const Vec3d& axis_y, const Vec3d& axis_z, const Vec3d& origin = Vec3d::all(0));

Which gets resolved after the change I mentioned. Is there something else I am missing?

Thanks! 👍

P.S. Automatic conversion operator doesn't work here because it can't change data type from float to double during conversion between Point and Vec.