GeographicLib  2.0
Geohash.cpp
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1 /**
2  * \file Geohash.cpp
3  * \brief Implementation for GeographicLib::Geohash class
4  *
5  * Copyright (c) Charles Karney (2012-2022) <charles@karney.com> and licensed
6  * under the MIT/X11 License. For more information, see
7  * https://geographiclib.sourceforge.io/
8  **********************************************************************/
9 
12 
13 namespace GeographicLib {
14 
15  using namespace std;
16 
17  const char* const Geohash::lcdigits_ = "0123456789bcdefghjkmnpqrstuvwxyz";
18  const char* const Geohash::ucdigits_ = "0123456789BCDEFGHJKMNPQRSTUVWXYZ";
19 
20  void Geohash::Forward(real lat, real lon, int len, string& geohash) {
21  using std::isnan; // Needed for Centos 7, ubuntu 14
22  static const real shift = ldexp(real(1), 45);
23  static const real loneps = Math::hd / shift;
24  static const real lateps = Math::qd / shift;
25  if (fabs(lat) > Math::qd)
26  throw GeographicErr("Latitude " + Utility::str(lat)
27  + "d not in [-" + to_string(Math::qd)
28  + "d, " + to_string(Math::qd) + "d]");
29  if (isnan(lat) || isnan(lon)) {
30  geohash = "invalid";
31  return;
32  }
33  if (lat == Math::qd) lat -= lateps / 2;
34  lon = Math::AngNormalize(lon);
35  if (lon == Math::hd) lon = -Math::hd; // lon now in [-180,180)
36  // lon/loneps in [-2^45,2^45); lon/loneps + shift in [0,2^46)
37  // similarly for lat
38  len = max(0, min(int(maxlen_), len));
39  unsigned long long
40  ulon = (unsigned long long)(floor(lon/loneps) + shift),
41  ulat = (unsigned long long)(floor(lat/lateps) + shift);
42  char geohash1[maxlen_];
43  unsigned byte = 0;
44  for (unsigned i = 0; i < 5 * unsigned(len);) {
45  if ((i & 1) == 0) {
46  byte = (byte << 1) + unsigned((ulon & mask_) != 0);
47  ulon <<= 1;
48  } else {
49  byte = (byte << 1) + unsigned((ulat & mask_) != 0);
50  ulat <<= 1;
51  }
52  ++i;
53  if (i % 5 == 0) {
54  geohash1[(i/5)-1] = lcdigits_[byte];
55  byte = 0;
56  }
57  }
58  geohash.resize(len);
59  copy(geohash1, geohash1 + len, geohash.begin());
60  }
61 
62  void Geohash::Reverse(const string& geohash, real& lat, real& lon,
63  int& len, bool centerp) {
64  static const real shift = ldexp(real(1), 45);
65  static const real loneps = Math::hd / shift;
66  static const real lateps = Math::qd / shift;
67  int len1 = min(int(maxlen_), int(geohash.length()));
68  if (len1 >= 3 &&
69  ((toupper(geohash[0]) == 'I' &&
70  toupper(geohash[1]) == 'N' &&
71  toupper(geohash[2]) == 'V') ||
72  // Check A first because it is not in a standard geohash
73  (toupper(geohash[1]) == 'A' &&
74  toupper(geohash[0]) == 'N' &&
75  toupper(geohash[2]) == 'N'))) {
76  lat = lon = Math::NaN();
77  return;
78  }
79  unsigned long long ulon = 0, ulat = 0;
80  for (unsigned k = 0, j = 0; k < unsigned(len1); ++k) {
81  int byte = Utility::lookup(ucdigits_, geohash[k]);
82  if (byte < 0)
83  throw GeographicErr("Illegal character in geohash " + geohash);
84  for (unsigned m = 16; m; m >>= 1) {
85  if (j == 0)
86  ulon = (ulon << 1) + unsigned((byte & m) != 0);
87  else
88  ulat = (ulat << 1) + unsigned((byte & m) != 0);
89  j ^= 1;
90  }
91  }
92  ulon <<= 1; ulat <<= 1;
93  if (centerp) {
94  ulon += 1;
95  ulat += 1;
96  }
97  int s = 5 * (maxlen_ - len1);
98  ulon <<= (s / 2);
99  ulat <<= s - (s / 2);
100  lon = ulon * loneps - Math::hd;
101  lat = ulat * lateps - Math::qd;
102  len = len1;
103  }
104 
105 } // namespace GeographicLib
GeographicLib::Math::real real
Definition: GeodSolve.cpp:31
Header for GeographicLib::Geohash class.
Header for GeographicLib::Utility class.
Exception handling for GeographicLib.
Definition: Constants.hpp:316
static void Forward(real lat, real lon, int len, std::string &geohash)
Definition: Geohash.cpp:20
static void Reverse(const std::string &geohash, real &lat, real &lon, int &len, bool centerp=true)
Definition: Geohash.cpp:62
static T AngNormalize(T x)
Definition: Math.cpp:71
static T NaN()
Definition: Math.cpp:250
@ hd
degrees per half turn
Definition: Math.hpp:144
@ qd
degrees per quarter turn
Definition: Math.hpp:141
static int lookup(const std::string &s, char c)
Definition: Utility.cpp:160
static std::string str(T x, int p=-1)
Definition: Utility.hpp:161
Namespace for GeographicLib.
Definition: Accumulator.cpp:12