Add h3EdgeLengthM function

dbms/src/Functions/h3EdgeLengthM.cpp

@@ -0,0 +1,82 @@
+#include "config_functions.h"
+#if USE_H3
+#    include <Columns/ColumnsNumber.h>
+#    include <DataTypes/DataTypesNumber.h>
+#    include <Functions/FunctionFactory.h>
+#    include <Functions/IFunction.h>
+#    include <Common/typeid_cast.h>
+#    include <ext/range.h>
+
+
+extern "C" {
+#    ifdef __clang__
+#        pragma clang diagnostic push
+#        pragma clang diagnostic ignored "-Wdocumentation"
+#    endif
+
+#    include <h3api.h>
+
+#    ifdef __clang__
+#        pragma clang diagnostic pop
+#    endif
+}
+
+namespace DB
+{
+// Average metric edge length of H3 hexagon. The edge length `e` for given resolution `res` can
+// be used for converting metric search radius `radius` to hexagon search ring size `k` that is
+// used by `H3kRing` function. For small enough search area simple flat approximation can be used,
+// i.e. the smallest `k` that satisfies relation `3 k^2 - 3 k + 1 >= (radius / e)^2` should be
+// chosen
+class FunctionH3EdgeLengthM : public IFunction
+{
+public:
+    static constexpr auto name = "h3EdgeLengthM";
+
+    static FunctionPtr create(const Context &) { return std::make_shared<FunctionH3EdgeLengthM>(); }
+
+    std::string getName() const override { return name; }
+
+    size_t getNumberOfArguments() const override { return 1; }
+    bool useDefaultImplementationForConstants() const override { return true; }
+
+    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
+    {
+        auto arg = arguments[0].get();
+        if (!WhichDataType(arg).isUInt8())
+            throw Exception(
+                "Illegal type " + arg->getName() + " of argument " + std::to_string(1) + " of function " + getName() + ". Must be UInt8",
+                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
+
+        return std::make_shared<DataTypeFloat64>();
+    }
+
+    void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
+    {
+        const auto col_hindex = block.getByPosition(arguments[0]).column.get();
+
+        auto dst = ColumnVector<Float64>::create();
+        auto & dst_data = dst->getData();
+        dst_data.resize(input_rows_count);
+
+        for (const auto row : ext::range(0, input_rows_count))
+        {
+            const int resolution = col_hindex->getUInt(row);
+
+            Float64 res = H3_EXPORT(edgeLengthM)(resolution);
+
+            dst_data[row] = res;
+        }
+
+        block.getByPosition(result).column = std::move(dst);
+    }
+};
+
+
+void registerFunctionH3EdgeLengthM(FunctionFactory & factory)
+{
+    factory.registerFunction<FunctionH3EdgeLengthM>();
+}
+
+}
+#endif

dbms/src/Functions/registerFunctionsGeo.cpp

@@ -14,6 +14,7 @@ void registerFunctionGeohashesInBox(FunctionFactory & factory);
 
 #if USE_H3
 void registerFunctionGeoToH3(FunctionFactory &);
+void registerFunctionH3EdgeLengthM(FunctionFactory &);
 void registerFunctionH3GetResolution(FunctionFactory &);
 void registerFunctionH3IsValid(FunctionFactory &);
 void registerFunctionH3KRing(FunctionFactory &);
@@ -30,6 +31,7 @@ void registerFunctionsGeo(FunctionFactory & factory)
 
 #if USE_H3
     registerFunctionGeoToH3(factory);
+	registerFunctionH3EdgeLengthM(factory);
 	registerFunctionH3GetResolution(factory);
 	registerFunctionH3IsValid(factory);
 	registerFunctionH3KRing(factory);

dbms/tests/queries/0_stateless/01043_h3_edge_length_m.reference

@@ -0,0 +1,2 @@
+418676.0055
+22606.3794

dbms/tests/queries/0_stateless/01043_h3_edge_length_m.sql

@@ -0,0 +1,2 @@
+SELECT h3EdgeLengthM(1);
+SELECT h3EdgeLengthM(4);