GeographicLib  1.51
OSGB.cpp
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1 /**
2  * \file OSGB.cpp
3  * \brief Implementation for GeographicLib::OSGB class
4  *
5  * Copyright (c) Charles Karney (2010-2020) <charles@karney.com> and licensed
6  * under the MIT/X11 License. For more information, see
7  * https://geographiclib.sourceforge.io/
8  **********************************************************************/
9 
10 #include <GeographicLib/OSGB.hpp>
12 
13 namespace GeographicLib {
14 
15  using namespace std;
16 
17  const char* const OSGB::letters_ = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
18  const char* const OSGB::digits_ = "0123456789";
19 
20  const TransverseMercator& OSGB::OSGBTM() {
21  static const TransverseMercator osgbtm(EquatorialRadius(), Flattening(),
22  CentralScale());
23  return osgbtm;
24  }
25 
26  Math::real OSGB::computenorthoffset() {
27  real x, y;
28  static const real northoffset =
29  ( OSGBTM().Forward(real(0), OriginLatitude(), real(0), x, y),
30  FalseNorthing() - y );
31  return northoffset;
32  }
33 
34  void OSGB::GridReference(real x, real y, int prec, std::string& gridref) {
35  using std::isnan; // Needed for Centos 7, ubuntu 14
36  CheckCoords(x, y);
37  if (!(prec >= 0 && prec <= maxprec_))
38  throw GeographicErr("OSGB precision " + Utility::str(prec)
39  + " not in [0, "
40  + Utility::str(int(maxprec_)) + "]");
41  if (isnan(x) || isnan(y)) {
42  gridref = "INVALID";
43  return;
44  }
45  char grid[2 + 2 * maxprec_];
46  int
47  xh = int(floor(x / tile_)),
48  yh = int(floor(y / tile_));
49  real
50  xf = x - tile_ * xh,
51  yf = y - tile_ * yh;
52  xh += tileoffx_;
53  yh += tileoffy_;
54  int z = 0;
55  grid[z++] = letters_[(tilegrid_ - (yh / tilegrid_) - 1)
56  * tilegrid_ + (xh / tilegrid_)];
57  grid[z++] = letters_[(tilegrid_ - (yh % tilegrid_) - 1)
58  * tilegrid_ + (xh % tilegrid_)];
59  // Need extra real because, since C++11, pow(float, int) returns double
60  real mult = real(pow(real(base_), max(tilelevel_ - prec, 0)));
61  int
62  ix = int(floor(xf / mult)),
63  iy = int(floor(yf / mult));
64  for (int c = min(prec, int(tilelevel_)); c--;) {
65  grid[z + c] = digits_[ ix % base_ ];
66  ix /= base_;
67  grid[z + c + prec] = digits_[ iy % base_ ];
68  iy /= base_;
69  }
70  if (prec > tilelevel_) {
71  xf -= floor(xf / mult);
72  yf -= floor(yf / mult);
73  mult = real(pow(real(base_), prec - tilelevel_));
74  ix = int(floor(xf * mult));
75  iy = int(floor(yf * mult));
76  for (int c = prec - tilelevel_; c--;) {
77  grid[z + c + tilelevel_] = digits_[ ix % base_ ];
78  ix /= base_;
79  grid[z + c + tilelevel_ + prec] = digits_[ iy % base_ ];
80  iy /= base_;
81  }
82  }
83  int mlen = z + 2 * prec;
84  gridref.resize(mlen);
85  copy(grid, grid + mlen, gridref.begin());
86  }
87 
88  void OSGB::GridReference(const std::string& gridref,
89  real& x, real& y, int& prec,
90  bool centerp) {
91  int
92  len = int(gridref.size()),
93  p = 0;
94  if (len >= 2 &&
95  toupper(gridref[0]) == 'I' &&
96  toupper(gridref[1]) == 'N') {
97  x = y = Math::NaN();
98  prec = -2; // For compatibility with MGRS::Reverse.
99  return;
100  }
101  char grid[2 + 2 * maxprec_];
102  for (int i = 0; i < len; ++i) {
103  if (!isspace(gridref[i])) {
104  if (p >= 2 + 2 * maxprec_)
105  throw GeographicErr("OSGB string " + gridref + " too long");
106  grid[p++] = gridref[i];
107  }
108  }
109  len = p;
110  p = 0;
111  if (len < 2)
112  throw GeographicErr("OSGB string " + gridref + " too short");
113  if (len % 2)
114  throw GeographicErr("OSGB string " + gridref +
115  " has odd number of characters");
116  int
117  xh = 0,
118  yh = 0;
119  while (p < 2) {
120  int i = Utility::lookup(letters_, grid[p++]);
121  if (i < 0)
122  throw GeographicErr("Illegal prefix character " + gridref);
123  yh = yh * tilegrid_ + tilegrid_ - (i / tilegrid_) - 1;
124  xh = xh * tilegrid_ + (i % tilegrid_);
125  }
126  xh -= tileoffx_;
127  yh -= tileoffy_;
128 
129  int prec1 = (len - p)/2;
130  real
131  unit = tile_,
132  x1 = unit * xh,
133  y1 = unit * yh;
134  for (int i = 0; i < prec1; ++i) {
135  unit /= base_;
136  int
137  ix = Utility::lookup(digits_, grid[p + i]),
138  iy = Utility::lookup(digits_, grid[p + i + prec1]);
139  if (ix < 0 || iy < 0)
140  throw GeographicErr("Encountered a non-digit in " + gridref);
141  x1 += unit * ix;
142  y1 += unit * iy;
143  }
144  if (centerp) {
145  x1 += unit/2;
146  y1 += unit/2;
147  }
148  x = x1;
149  y = y1;
150  prec = prec1;
151  }
152 
153  void OSGB::CheckCoords(real x, real y) {
154  // Limits are all multiples of 100km and are all closed on the lower end
155  // and open on the upper end -- and this is reflected in the error
156  // messages. NaNs are let through.
157  if (x < minx_ || x >= maxx_)
158  throw GeographicErr("Easting " + Utility::str(int(floor(x/1000)))
159  + "km not in OSGB range ["
160  + Utility::str(minx_/1000) + "km, "
161  + Utility::str(maxx_/1000) + "km)");
162  if (y < miny_ || y >= maxy_)
163  throw GeographicErr("Northing " + Utility::str(int(floor(y/1000)))
164  + "km not in OSGB range ["
165  + Utility::str(miny_/1000) + "km, "
166  + Utility::str(maxy_/1000) + "km)");
167  }
168 
169 } // namespace GeographicLib
GeographicLib::Math::real real
Definition: GeodSolve.cpp:31
Header for GeographicLib::Utility class.
Header for GeographicLib::OSGB class.
Namespace for GeographicLib.
Definition: Accumulator.cpp:12
static T NaN()
Definition: Math.cpp:268
static std::string str(T x, int p=-1)
Definition: Utility.hpp:276
static void GridReference(real x, real y, int prec, std::string &gridref)
Definition: OSGB.cpp:34
Exception handling for GeographicLib.
Definition: Constants.hpp:315
static int lookup(const std::string &s, char c)
Definition: Utility.hpp:461