使用 boost::units 计算地理坐标

问题描述

我正在尝试对 [计算纬度/经度点之间的距离、方位和更多][1] 中的公式进行类型安全的 C++ 实现。不幸的是，我遇到了 C++ 类型的错误，这些错误将实际问题隐藏在无休止的模板扩展下。我想我真的很接近：

#include <iostream>
#include <boost/units/systems/angle/degrees.hpp>
#include <boost/units/systems/si/length.hpp>
#include <boost/units/systems/si/plane_angle.hpp>
#include <boost/units/systems/si/prefixes.hpp>
#include <boost/units/cmath.hpp>
#include <boost/units/io.hpp>

using namespace boost::units;
using namespace boost::units::si;

struct Position
{
public:
    using angle_type = quantity<degree::plane_angle>;
    Position(const angle_type &latitude,const angle_type &longitude) : m_latitude{latitude},m_longitude{longitude} {}
    angle_type m_latitude;
    angle_type m_longitude;
};

const quantity<si::length> earth_radius{6371. * kilo * meters};

Position move(const Position &start,quantity<degree::plane_angle> bearing,quantity<si::length> distance)
{
    const auto angular_distance = distance / earth_radius;

    auto latitude2 = asin(sin(start.m_latitude) * cos(angular_distance) +
                          cos(start.m_latitude) * sin(angular_distance) * cos(bearing));

    auto longitude2 = start.m_longitude + atan2(sin(bearing) * sin(angular_distance) * cos(start.m_latitude),cos(angular_distance) - sin(start.m_latitude) * sin(latitude2));
    return Position(latitude2,longitude2);
}

int main(int,char **)
{
    return 0;
}

错误信息：

/home/jpo/src/units/main.cpp:30:41: error: no match for ‘operator+’
(operand types are ‘const angle_type’ and ‘double’)

   30 |     auto longitude2 = start.m_longitude + atan2(sin(bearing) * sin(angular_distance) * cos(start.m_latitude),|                       ~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                             |                  |
      |                             |                  double
      |                             const angle_type

解决方法

问题在于

const auto angular_distance = distance / earth_radius;

在应该是角度时是无量纲的。将此更改为

quantity<degree::plane_angle> angular_distance{(distance / earth_radius).value() * radians};

使代码编译。