GeographicLib  1.52
Geohash.cpp
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1 /**
2  * \file Geohash.cpp
3  * \brief Implementation for GeographicLib::Geohash class
4  *
5  * Copyright (c) Charles Karney (2012-2020) <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 = 180 / shift;
24  static const real lateps = 90 / shift;
25  if (abs(lat) > 90)
26  throw GeographicErr("Latitude " + Utility::str(lat)
27  + "d not in [-90d, 90d]");
28  if (isnan(lat) || isnan(lon)) {
29  geohash = "invalid";
30  return;
31  }
32  if (lat == 90) lat -= lateps / 2;
33  lon = Math::AngNormalize(lon);
34  if (lon == 180) lon = -180; // lon now in [-180,180)
35  // lon/loneps in [-2^45,2^45); lon/loneps + shift in [0,2^46)
36  // similarly for lat
37  len = max(0, min(int(maxlen_), len));
38  unsigned long long
39  ulon = (unsigned long long)(floor(lon/loneps) + shift),
40  ulat = (unsigned long long)(floor(lat/lateps) + shift);
41  char geohash1[maxlen_];
42  unsigned byte = 0;
43  for (unsigned i = 0; i < 5 * unsigned(len);) {
44  if ((i & 1) == 0) {
45  byte = (byte << 1) + unsigned((ulon & mask_) != 0);
46  ulon <<= 1;
47  } else {
48  byte = (byte << 1) + unsigned((ulat & mask_) != 0);
49  ulat <<= 1;
50  }
51  ++i;
52  if (i % 5 == 0) {
53  geohash1[(i/5)-1] = lcdigits_[byte];
54  byte = 0;
55  }
56  }
57  geohash.resize(len);
58  copy(geohash1, geohash1 + len, geohash.begin());
59  }
60 
61  void Geohash::Reverse(const string& geohash, real& lat, real& lon,
62  int& len, bool centerp) {
63  static const real shift = ldexp(real(1), 45);
64  static const real loneps = 180 / shift;
65  static const real lateps = 90 / shift;
66  int len1 = min(int(maxlen_), int(geohash.length()));
67  if (len1 >= 3 &&
68  ((toupper(geohash[0]) == 'I' &&
69  toupper(geohash[1]) == 'N' &&
70  toupper(geohash[2]) == 'V') ||
71  // Check A first because it is not in a standard geohash
72  (toupper(geohash[1]) == 'A' &&
73  toupper(geohash[0]) == 'N' &&
74  toupper(geohash[2]) == 'N'))) {
75  lat = lon = Math::NaN();
76  return;
77  }
78  unsigned long long ulon = 0, ulat = 0;
79  for (unsigned k = 0, j = 0; k < unsigned(len1); ++k) {
80  int byte = Utility::lookup(ucdigits_, geohash[k]);
81  if (byte < 0)
82  throw GeographicErr("Illegal character in geohash " + geohash);
83  for (unsigned m = 16; m; m >>= 1) {
84  if (j == 0)
85  ulon = (ulon << 1) + unsigned((byte & m) != 0);
86  else
87  ulat = (ulat << 1) + unsigned((byte & m) != 0);
88  j ^= 1;
89  }
90  }
91  ulon <<= 1; ulat <<= 1;
92  if (centerp) {
93  ulon += 1;
94  ulat += 1;
95  }
96  int s = 5 * (maxlen_ - len1);
97  ulon <<= (s / 2);
98  ulat <<= s - (s / 2);
99  lon = ulon * loneps - 180;
100  lat = ulat * lateps - 90;
101  len = len1;
102  }
103 
104 } // 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:315
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:61
static T AngNormalize(T x)
Definition: Math.hpp:420
static T NaN()
Definition: Math.cpp:260
static int lookup(const std::string &s, char c)
Definition: Utility.hpp:461
static std::string str(T x, int p=-1)
Definition: Utility.hpp:276
Namespace for GeographicLib.
Definition: Accumulator.cpp:12