ClickHouse/src/Functions/h3EdgeLengthM.cpp

#if !defined(ARCADIA_BUILD)
#    include "config_functions.h"
#endif

#if USE_H3

#include <Columns/ColumnsNumber.h>
#include <DataTypes/DataTypesNumber.h>
#include <Functions/FunctionFactory.h>
#include <Functions/IFunction.h>
#include <IO/WriteHelpers.h>
#include <Common/typeid_cast.h>
#include <ext/range.h>

#include <constants.h>
#include <h3api.h>


namespace DB
{
namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
    extern const int ARGUMENT_OUT_OF_BOUND;
}

namespace
{

// 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
    {
        const 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>();
    }

    ColumnPtr executeImpl(ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
    {
        const auto * col_hindex = 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 UInt64 resolution = col_hindex->getUInt(row);
            if (resolution > MAX_H3_RES)
                throw Exception("The argument 'resolution' (" + toString(resolution) + ") of function " + getName()
                    + " is out of bounds because the maximum resolution in H3 library is " + toString(MAX_H3_RES), ErrorCodes::ARGUMENT_OUT_OF_BOUND);

            Float64 res = edgeLengthM(resolution);

            dst_data[row] = res;
        }

        return dst;
    }
};

}

void registerFunctionH3EdgeLengthM(FunctionFactory & factory)
{
    factory.registerFunction<FunctionH3EdgeLengthM>();
}

}

#endif