Geohash.hpp

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#if !defined(GEOGRAPHICLIB_GEOHASH_HPP)
#define GEOGRAPHICLIB_GEOHASH_HPP 1

#include <GeographicLib/Constants.hpp>

#if defined(_MSC_VER)
// Squelch warnings about dll vs string
#  pragma warning (push)
#  pragma warning (disable: 4251)
#endif

namespace GeographicLib {

  class GEOGRAPHICLIB_EXPORT Geohash {
  private:
    typedef Math::real real;
    static const int maxlen_ = 18;
    static const unsigned long long mask_ = 1ULL << 45;
    static const char* const lcdigits_;
    static const char* const ucdigits_;
    Geohash();                     // Disable constructor

  public:

    static void Forward(real lat, real lon, int len, std::string& geohash);

    static void Reverse(const std::string& geohash, real& lat, real& lon,
                        int& len, bool centerp = true);

    static Math::real LatitudeResolution(int len) {
      using std::ldexp;
      len = (std::max)(0, (std::min)(int(maxlen_), len));
      return ldexp(real(180), -(5 * len / 2));
    }

    static Math::real LongitudeResolution(int len) {
      using std::ldexp;
      len = (std::max)(0, (std::min)(int(maxlen_), len));
      return ldexp(real(360), -(5 * len - 5 * len / 2));
    }

    static int GeohashLength(real res) {
      using std::abs; res = abs(res);
      for (int len = 0; len < maxlen_; ++len)
        if (LongitudeResolution(len) <= res)
          return len;
      return maxlen_;
    }

    static int GeohashLength(real latres, real lonres) {
      using std::abs;
      latres = abs(latres);
      lonres = abs(lonres);
      for (int len = 0; len < maxlen_; ++len)
        if (LatitudeResolution(len) <= latres &&
            LongitudeResolution(len) <= lonres)
          return len;
      return maxlen_;
    }

    static int DecimalPrecision(int len) {
      using std::floor; using std::log;
      return -int(floor(log(LatitudeResolution(len))/log(Math::real(10))));
    }

  };

} // namespace GeographicLib

#if defined(_MSC_VER)
#  pragma warning (pop)
#endif

#endif  // GEOGRAPHICLIB_GEOHASH_HPP