<=> operator for OpenCV type: binary '<': no operator found which takes a left-hand operand of type 'const _Ty' (or there is no acceptable conversion)

Question

I want a function to return an std::set of cv::Point3d, this means an implementation of < is required (no operator "<" matches these operands error), so i implemented the <=> operator for the generic type cv::Point3_, however I am still getting a binary '<': no operator found which takes a left-hand operand of type 'const _Ty' (or there is no acceptable conversion) error.

While I managed to compile an implementation for a custom type:

#include <iostream>
#include <compare>
#include <tuple>
#include <set>
#include <vector>
#include <algorithm>

template<typename _Tp> class Point3_
{
public:

   Point3_(_Tp _x, _Tp _y, _Tp _z);

   _Tp x;
   _Tp y;
   _Tp z;
};

template<typename _Tp> inline
Point3_<_Tp>::Point3_(_Tp _x, _Tp _y, _Tp _z)
   : x(_x), y(_y), z(_z) {}

// Function definition for 'operator<=>' not found warning.
template<typename _Tp> std::partial_ordering operator<=>(const Point3_<_Tp>& pt1, const Point3_<_Tp>& pt2);

template<typename _Tp> inline std::partial_ordering operator<=>(const Point3_<_Tp>& pt1, const Point3_<_Tp>& pt2)
{
   auto as_tie = [](const Point3_<_Tp>& pt) { return std::tie(pt.x, pt.y, pt.z); };
   return as_tie(pt1) <=> as_tie(pt2);
}

int main()
{

   auto a = Point3_<double>(-.1, -.1, -.1);
   auto b = Point3_<double>(.1, .1, .1);
   auto c = Point3_<double>(.2, .2, .2);

   std::set<Point3_<double>> dset;
   std::vector<Point3_<double>> dvec = { a, b, c };

   std::ranges::copy_if(dvec.begin(), dvec.end(), std::inserter(dset, dset.begin()), [](auto p) { return p.x > 0; });

   std::cout << "(-.1, -.1, -.1) < (.1, .1, .1) is " << (a < b ? "true" : "false") << std::endl << "The set contains: ";
   for (auto& pt : dset)
   {
      std::cout << " (" << pt.x << " " << pt.y << " " << pt.z << ")";
   }
   std::cout << std::endl;

}

It does not compile for the desired type (error mentioned above):

#include <iostream>
#include <compare>
#include <tuple>
#include <set>
#include <vector>
#include <algorithm>
#include <opencv2/opencv.hpp>

// Function definition for 'operator<=>' not found warning.
template<typename _Tp>
std::partial_ordering operator<=>(const cv::Point3_<_Tp>& pt1, const cv::Point3_<_Tp>& pt2);

template<typename _Tp>
inline std::partial_ordering operator<=>(const cv::Point3_<_Tp>& pt1, const cv::Point3_<_Tp>& pt2)
{
   auto as_tie = [](const cv::Point3_<_Tp>& pt) { return std::tie(pt.x, pt.y, pt.z); };
   return as_tie(pt1) <=> as_tie(pt2);
}

int main()
{

   auto a = cv::Point3_<double>(-.1, -.1, -.1);
   auto b = cv::Point3_<double>(.1, .1, .1);
   auto c = cv::Point3_<double>(.2, .2, .2);

   std::set<cv::Point3_<double>> dset;
   std::vector<cv::Point3_<double>> dvec = { a, b, c };

   std::ranges::copy_if(dvec.begin(), dvec.end(), std::inserter(dset, dset.begin()), [](auto p) { return p.x > 0; });

   std::cout << "(-.1, -.1, -.1) < (.1, .1, .1) is " << (a < b ? "true" : "false") << std::endl << "The set contains: ";
   for (auto& pt : dset)
   {
      std::cout << " (" << pt.x << " " << pt.y << " " << pt.z << ")";
   }
   std::cout << std::endl;

}

OpenCV version: 4.6.0 (installed with vcpkg)

Compiler: MSVC, default compiler options bundled with VS2022. Only the C++ Language Standard option has been changed (to C++20).