feat: support for convertibility of point origins added

src/core/include/mp_units/bits/quantity_point_concepts.h

@@ -98,7 +98,7 @@ concept QuantityPointOf =
   QuantityPoint<QP> &&
   (ReferenceOf<std::remove_const_t<decltype(QP::reference)>, V> ||
    (PointOrigin<std::remove_const_t<decltype(V)>> &&
-    std::same_as<std::remove_const_t<decltype(QP::absolute_point_origin)>, std::remove_const_t<decltype(V)>>));
+    std::convertible_to<std::remove_const_t<decltype(QP::absolute_point_origin)>, std::remove_const_t<decltype(V)>>));
 
 /**
  * @brief A concept matching all external quantity point like types

src/core/include/mp_units/quantity_point.h

@@ -1,4 +1,3 @@
-
 // The MIT License (MIT)
 //
 // Copyright (c) 2018 Mateusz Pusz
@@ -33,6 +32,12 @@ namespace mp_units {
 template<QuantitySpec auto Q>
 struct absolute_point_origin {
   static constexpr QuantitySpec auto quantity_spec = Q;
+  absolute_point_origin() = default;
+  template<QuantitySpec auto Q2>
+    requires(implicitly_convertible(Q2, Q))
+  consteval absolute_point_origin(absolute_point_origin<Q2>)
+  {
+  }
 };
 
 namespace detail {