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diff --git a/boost/geometry/core/coordinate_promotion.hpp b/boost/geometry/core/coordinate_promotion.hpp
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+++ b/boost/geometry/core/coordinate_promotion.hpp
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+// Boost.Geometry
+
+// Copyright (c) 2021 Barend Gehrels, Amsterdam, the Netherlands.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_GEOMETRY_CORE_COORDINATE_PROMOTION_HPP
+#define BOOST_GEOMETRY_CORE_COORDINATE_PROMOTION_HPP
+
+#include <boost/geometry/core/coordinate_type.hpp>
+
+// TODO: move this to a future headerfile implementing traits for these types
+#include <boost/rational.hpp>
+#include <boost/multiprecision/cpp_bin_float.hpp>
+#include <boost/multiprecision/cpp_int.hpp>
+
+namespace boost { namespace geometry
+{
+
+namespace traits
+{
+
+// todo
+
+} // namespace traits
+
+/*!
+    \brief Meta-function converting, if necessary, to "a floating point" type
+    \details
+        - if input type is integer, type is double
+        - else type is input type
+    \ingroup utility
+ */
+// TODO: replace with, or call, promoted_to_floating_point
+template <typename T, typename PromoteIntegerTo = double>
+struct promote_floating_point
+{
+    typedef std::conditional_t
+        <
+            std::is_integral<T>::value,
+            PromoteIntegerTo,
+            T
+        > type;
+};
+
+// TODO: replace with promoted_to_floating_point
+template <typename Geometry>
+struct fp_coordinate_type
+{
+    typedef typename promote_floating_point
+        <
+            typename coordinate_type<Geometry>::type
+        >::type type;
+};
+
+namespace detail
+{
+
+// Promote any integral type to double. Floating point
+// and other user defined types stay as they are, unless specialized.
+// TODO: we shold add a coordinate_promotion traits for promotion to
+// floating point or (larger) integer types.
+template <typename Type>
+struct promoted_to_floating_point
+{
+    using type = std::conditional_t
+        <
+            std::is_integral<Type>::value, double, Type
+        >;
+};
+
+// Boost.Rational goes to double
+template <typename T>
+struct promoted_to_floating_point<boost::rational<T>>
+{
+    using type = double;
+};
+
+// Any Boost.Multiprecision goes to double (for example int128_t),
+// unless specialized
+template <typename Backend>
+struct promoted_to_floating_point<boost::multiprecision::number<Backend>>
+{
+    using type = double;
+};
+
+// Boost.Multiprecision binary floating point numbers are used as FP.
+template <unsigned Digits>
+struct promoted_to_floating_point
+    <
+        boost::multiprecision::number
+            <
+                boost::multiprecision::cpp_bin_float<Digits>
+            >
+    >
+{
+    using type = boost::multiprecision::number
+        <
+            boost::multiprecision::cpp_bin_float<Digits>
+        >;
+};
+
+}
+
+
+}} // namespace boost::geometry
+
+
+#endif // BOOST_GEOMETRY_CORE_COORDINATE_PROMOTION_HPP