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Geohash.hpp
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/**
* \file Geohash.hpp
* \brief Header for GeographicLib::Geohash class
*
* Copyright (c) Charles Karney (2012-2022) <karney@alum.mit.edu> and licensed
* under the MIT/X11 License. For more information, see
* https://geographiclib.sourceforge.io/
**********************************************************************/
#if !defined(GEOGRAPHICLIB_GEOHASH_HPP)
#define GEOGRAPHICLIB_GEOHASH_HPP 1
#include <GeographicLib/Constants.hpp>
namespace GeographicLib {
/**
* \brief Conversions for geohashes
*
* Geohashes are described in
* - https://en.wikipedia.org/wiki/Geohash
* - http://geohash.org/
* .
* They provide a compact string representation of a particular geographic
* location (expressed as latitude and longitude), with the property that if
* trailing characters are dropped from the string the geographic location
* remains nearby. The classes Georef and GARS implement similar compact
* representations.
*
* Example of use:
* \include example-Geohash.cpp
**********************************************************************/
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() = delete; // Disable constructor
public:
/**
* Convert from geographic coordinates to a geohash.
*
* @param[in] lat latitude of point (degrees).
* @param[in] lon longitude of point (degrees).
* @param[in] len the length of the resulting geohash.
* @param[out] geohash the geohash.
* @exception GeographicErr if \e lat is not in [&minus;90&deg;,
* 90&deg;].
* @exception std::bad_alloc if memory for \e geohash can't be allocated.
*
* Internally, \e len is first put in the range [0, 18]. (\e len = 18
* provides approximately 1&mu;m precision.)
*
* If \e lat or \e lon is NaN, the returned geohash is "invalid".
**********************************************************************/
static void Forward(real lat, real lon, int len, std::string& geohash);
/**
* Convert from a geohash to geographic coordinates.
*
* @param[in] geohash the geohash.
* @param[out] lat latitude of point (degrees).
* @param[out] lon longitude of point (degrees).
* @param[out] len the length of the geohash.
* @param[in] centerp if true (the default) return the center of the
* geohash location, otherwise return the south-west corner.
* @exception GeographicErr if \e geohash contains illegal characters.
*
* Only the first 18 characters for \e geohash are considered. (18
* characters provides approximately 1&mu;m precision.) The case of the
* letters in \e geohash is ignored.
*
* If the first 3 characters of \e geohash are "inv", then \e lat and \e
* lon are set to NaN and \e len is unchanged. ("nan" is treated
* similarly.)
**********************************************************************/
static void Reverse(const std::string& geohash, real& lat, real& lon,
int& len, bool centerp = true);
/**
* The latitude resolution of a geohash.
*
* @param[in] len the length of the geohash.
* @return the latitude resolution (degrees).
*
* Internally, \e len is first put in the range [0, 18].
**********************************************************************/
static Math::real LatitudeResolution(int len) {
using std::ldexp;
len = (std::max)(0, (std::min)(int(maxlen_), len));
return ldexp(real(Math::hd), -(5 * len / 2));
}
/**
* The longitude resolution of a geohash.
*
* @param[in] len the length of the geohash.
* @return the longitude resolution (degrees).
*
* Internally, \e len is first put in the range [0, 18].
**********************************************************************/
static Math::real LongitudeResolution(int len) {
using std::ldexp;
len = (std::max)(0, (std::min)(int(maxlen_), len));
return ldexp(real(Math::td), -(5 * len - 5 * len / 2));
}
/**
* The geohash length required to meet a given geographic resolution.
*
* @param[in] res the minimum of resolution in latitude and longitude
* (degrees).
* @return geohash length.
*
* The returned length is in the range [0, 18].
**********************************************************************/
static int GeohashLength(real res) {
using std::fabs; res = fabs(res);
for (int len = 0; len < maxlen_; ++len)
if (LongitudeResolution(len) <= res)
return len;
return maxlen_;
}
/**
* The geohash length required to meet a given geographic resolution.
*
* @param[in] latres the resolution in latitude (degrees).
* @param[in] lonres the resolution in longitude (degrees).
* @return geohash length.
*
* The returned length is in the range [0, 18].
**********************************************************************/
static int GeohashLength(real latres, real lonres) {
using std::fabs;
latres = fabs(latres);
lonres = fabs(lonres);
for (int len = 0; len < maxlen_; ++len)
if (LatitudeResolution(len) <= latres &&
LongitudeResolution(len) <= lonres)
return len;
return maxlen_;
}
/**
* The decimal geographic precision required to match a given geohash
* length. This is the number of digits needed after decimal point in a
* decimal degrees representation.
*
* @param[in] len the length of the geohash.
* @return the decimal precision (may be negative).
*
* Internally, \e len is first put in the range [0, 18]. The returned
* decimal precision is in the range [&minus;2, 12].
**********************************************************************/
static int DecimalPrecision(int len) {
using std::floor; using std::log;
return -int(floor(log(LatitudeResolution(len))/log(Math::real(10))));
}
};
} // namespace GeographicLib
#endif // GEOGRAPHICLIB_GEOHASH_HPP
Constants.hpp
Header for GeographicLib::Constants class.
GEOGRAPHICLIB_EXPORT
#define GEOGRAPHICLIB_EXPORT
Definition Constants.hpp:67
real
GeographicLib::Math::real real
Definition GeodSolve.cpp:28
GeographicLib::Geohash
Conversions for geohashes.
Definition Geohash.hpp:34
GeographicLib::Geohash::LatitudeResolution
static Math::real LatitudeResolution(int len)
Definition Geohash.hpp:93
GeographicLib::Geohash::DecimalPrecision
static int DecimalPrecision(int len)
Definition Geohash.hpp:161
GeographicLib::Geohash::LongitudeResolution
static Math::real LongitudeResolution(int len)
Definition Geohash.hpp:107
GeographicLib::Geohash::GeohashLength
static int GeohashLength(real latres, real lonres)
Definition Geohash.hpp:139
GeographicLib::Geohash::GeohashLength
static int GeohashLength(real res)
Definition Geohash.hpp:122
GeographicLib::Math::real
double real
Definition Math.hpp:115
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12