GeographicLib  1.48
Geoid.hpp
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1 /**
2  * \file Geoid.hpp
3  * \brief Header for GeographicLib::Geoid class
4  *
5  * Copyright (c) Charles Karney (2009-2015) <charles@karney.com> and licensed
6  * under the MIT/X11 License. For more information, see
7  * https://geographiclib.sourceforge.io/
8  **********************************************************************/
9 
10 #if !defined(GEOGRAPHICLIB_GEOID_HPP)
11 #define GEOGRAPHICLIB_GEOID_HPP 1
12 
13 #include <vector>
14 #include <fstream>
16 
17 #if defined(_MSC_VER)
18 // Squelch warnings about dll vs vector and constant conditional expressions
19 # pragma warning (push)
20 # pragma warning (disable: 4251 4127)
21 #endif
22 
23 #if !defined(GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH)
24 /**
25  * The size of the pixel data in the pgm data files for the geoids. 2 is the
26  * standard size corresponding to a maxval 2<sup>16</sup>&minus;1. Setting it
27  * to 4 uses a maxval of 2<sup>32</sup>&minus;1 and changes the extension for
28  * the data files from .pgm to .pgm4. Note that the format of these pgm4 files
29  * is a non-standard extension of the pgm format.
30  **********************************************************************/
31 # define GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH 2
32 #endif
33 
34 namespace GeographicLib {
35 
36  /**
37  * \brief Looking up the height of the geoid above the ellipsoid
38  *
39  * This class evaluates the height of one of the standard geoids, EGM84,
40  * EGM96, or EGM2008 by bilinear or cubic interpolation into a rectangular
41  * grid of data. These geoid models are documented in
42  * - EGM84:
43  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/wgs84_180.html
44  * - EGM96:
45  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html
46  * - EGM2008:
47  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008
48  *
49  * The geoids are defined in terms of spherical harmonics. However in order
50  * to provide a quick and flexible method of evaluating the geoid heights,
51  * this class evaluates the height by interpolation into a grid of
52  * precomputed values.
53  *
54  * The height of the geoid above the ellipsoid, \e N, is sometimes called the
55  * geoid undulation. It can be used to convert a height above the ellipsoid,
56  * \e h, to the corresponding height above the geoid (the orthometric height,
57  * roughly the height above mean sea level), \e H, using the relations
58  *
59  * &nbsp;&nbsp;&nbsp;\e h = \e N + \e H;
60  * &nbsp;&nbsp;\e H = &minus;\e N + \e h.
61  *
62  * See \ref geoid for details of how to install the data sets, the data
63  * format, estimates of the interpolation errors, and how to use caching.
64  *
65  * This class is typically \e not thread safe in that a single instantiation
66  * cannot be safely used by multiple threads because of the way the object
67  * reads the data set and because it maintains a single-cell cache. If
68  * multiple threads need to calculate geoid heights they should all construct
69  * thread-local instantiations. Alternatively, set the optional \e
70  * threadsafe parameter to true in the constructor. This causes the
71  * constructor to read all the data into memory and to turn off the
72  * single-cell caching which results in a Geoid object which \e is thread
73  * safe.
74  *
75  * Example of use:
76  * \include example-Geoid.cpp
77  *
78  * <a href="GeoidEval.1.html">GeoidEval</a> is a command-line utility
79  * providing access to the functionality of Geoid.
80  **********************************************************************/
81 
83  private:
84  typedef Math::real real;
85 #if GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH != 4
86  typedef unsigned short pixel_t;
87  static const unsigned pixel_size_ = 2;
88  static const unsigned pixel_max_ = 0xffffu;
89 #else
90  typedef unsigned pixel_t;
91  static const unsigned pixel_size_ = 4;
92  static const unsigned pixel_max_ = 0xffffffffu;
93 #endif
94  static const unsigned stencilsize_ = 12;
95  static const unsigned nterms_ = ((3 + 1) * (3 + 2))/2; // for a cubic fit
96  static const int c0_;
97  static const int c0n_;
98  static const int c0s_;
99  static const int c3_[stencilsize_ * nterms_];
100  static const int c3n_[stencilsize_ * nterms_];
101  static const int c3s_[stencilsize_ * nterms_];
102 
103  std::string _name, _dir, _filename;
104  const bool _cubic;
105  const real _a, _e2, _degree, _eps;
106  mutable std::ifstream _file;
107  real _rlonres, _rlatres;
108  std::string _description, _datetime;
109  real _offset, _scale, _maxerror, _rmserror;
110  int _width, _height;
111  unsigned long long _datastart, _swidth;
112  bool _threadsafe;
113  // Area cache
114  mutable std::vector< std::vector<pixel_t> > _data;
115  mutable bool _cache;
116  // NE corner and extent of cache
117  mutable int _xoffset, _yoffset, _xsize, _ysize;
118  // Cell cache
119  mutable int _ix, _iy;
120  mutable real _v00, _v01, _v10, _v11;
121  mutable real _t[nterms_];
122  void filepos(int ix, int iy) const {
123  _file.seekg(
124 #if !(defined(__GNUC__) && __GNUC__ < 4)
125  // g++ 3.x doesn't know about the cast to streamoff.
126  std::ios::streamoff
127 #endif
128  (_datastart +
129  pixel_size_ * (unsigned(iy)*_swidth + unsigned(ix))));
130  }
131  real rawval(int ix, int iy) const {
132  if (ix < 0)
133  ix += _width;
134  else if (ix >= _width)
135  ix -= _width;
136  if (_cache && iy >= _yoffset && iy < _yoffset + _ysize &&
137  ((ix >= _xoffset && ix < _xoffset + _xsize) ||
138  (ix + _width >= _xoffset && ix + _width < _xoffset + _xsize))) {
139  return real(_data[iy - _yoffset]
140  [ix >= _xoffset ? ix - _xoffset : ix + _width - _xoffset]);
141  } else {
142  if (iy < 0 || iy >= _height) {
143  iy = iy < 0 ? -iy : 2 * (_height - 1) - iy;
144  ix += (ix < _width/2 ? 1 : -1) * _width/2;
145  }
146  try {
147  filepos(ix, iy);
148  // initial values to suppress warnings in case get fails
149  char a = 0, b = 0;
150  _file.get(a);
151  _file.get(b);
152  unsigned r = ((unsigned char)(a) << 8) | (unsigned char)(b);
153  if (pixel_size_ == 4) {
154  _file.get(a);
155  _file.get(b);
156  r = (r << 16) | ((unsigned char)(a) << 8) | (unsigned char)(b);
157  }
158  return real(r);
159  }
160  catch (const std::exception& e) {
161  // throw GeographicErr("Error reading " + _filename + ": "
162  // + e.what());
163  // triggers complaints about the "binary '+'" under Visual Studio.
164  // So use '+=' instead.
165  std::string err("Error reading ");
166  err += _filename;
167  err += ": ";
168  err += e.what();
169  throw GeographicErr(err);
170  }
171  }
172  }
173  real height(real lat, real lon) const;
174  Geoid(const Geoid&); // copy constructor not allowed
175  Geoid& operator=(const Geoid&); // copy assignment not allowed
176  public:
177 
178  /**
179  * Flags indicating conversions between heights above the geoid and heights
180  * above the ellipsoid.
181  **********************************************************************/
182  enum convertflag {
183  /**
184  * The multiplier for converting from heights above the geoid to heights
185  * above the ellipsoid.
186  **********************************************************************/
187  ELLIPSOIDTOGEOID = -1,
188  /**
189  * No conversion.
190  **********************************************************************/
191  NONE = 0,
192  /**
193  * The multiplier for converting from heights above the ellipsoid to
194  * heights above the geoid.
195  **********************************************************************/
196  GEOIDTOELLIPSOID = 1,
197  };
198 
199  /** \name Setting up the geoid
200  **********************************************************************/
201  ///@{
202  /**
203  * Construct a geoid.
204  *
205  * @param[in] name the name of the geoid.
206  * @param[in] path (optional) directory for data file.
207  * @param[in] cubic (optional) interpolation method; false means bilinear,
208  * true (the default) means cubic.
209  * @param[in] threadsafe (optional), if true, construct a thread safe
210  * object. The default is false
211  * @exception GeographicErr if the data file cannot be found, is
212  * unreadable, or is corrupt.
213  * @exception GeographicErr if \e threadsafe is true but the memory
214  * necessary for caching the data can't be allocated.
215  *
216  * The data file is formed by appending ".pgm" to the name. If \e path is
217  * specified (and is non-empty), then the file is loaded from directory, \e
218  * path. Otherwise the path is given by DefaultGeoidPath(). If the \e
219  * threadsafe parameter is true, the data set is read into memory, the data
220  * file is closed, and single-cell caching is turned off; this results in a
221  * Geoid object which \e is thread safe.
222  **********************************************************************/
223  explicit Geoid(const std::string& name, const std::string& path = "",
224  bool cubic = true, bool threadsafe = false);
225 
226  /**
227  * Set up a cache.
228  *
229  * @param[in] south latitude (degrees) of the south edge of the cached area.
230  * @param[in] west longitude (degrees) of the west edge of the cached area.
231  * @param[in] north latitude (degrees) of the north edge of the cached area.
232  * @param[in] east longitude (degrees) of the east edge of the cached area.
233  * @exception GeographicErr if the memory necessary for caching the data
234  * can't be allocated (in this case, you will have no cache and can try
235  * again with a smaller area).
236  * @exception GeographicErr if there's a problem reading the data.
237  * @exception GeographicErr if this is called on a threadsafe Geoid.
238  *
239  * Cache the data for the specified "rectangular" area bounded by the
240  * parallels \e south and \e north and the meridians \e west and \e east.
241  * \e east is always interpreted as being east of \e west, if necessary by
242  * adding 360&deg; to its value. \e south and \e north should be in
243  * the range [&minus;90&deg;, 90&deg;].
244  **********************************************************************/
245  void CacheArea(real south, real west, real north, real east) const;
246 
247  /**
248  * Cache all the data.
249  *
250  * @exception GeographicErr if the memory necessary for caching the data
251  * can't be allocated (in this case, you will have no cache and can try
252  * again with a smaller area).
253  * @exception GeographicErr if there's a problem reading the data.
254  * @exception GeographicErr if this is called on a threadsafe Geoid.
255  *
256  * On most computers, this is fast for data sets with grid resolution of 5'
257  * or coarser. For a 1' grid, the required RAM is 450MB; a 2.5' grid needs
258  * 72MB; and a 5' grid needs 18MB.
259  **********************************************************************/
260  void CacheAll() const { CacheArea(real(-90), real(0),
261  real(90), real(360)); }
262 
263  /**
264  * Clear the cache. This never throws an error. (This does nothing with a
265  * thread safe Geoid.)
266  **********************************************************************/
267  void CacheClear() const;
268 
269  ///@}
270 
271  /** \name Compute geoid heights
272  **********************************************************************/
273  ///@{
274  /**
275  * Compute the geoid height at a point
276  *
277  * @param[in] lat latitude of the point (degrees).
278  * @param[in] lon longitude of the point (degrees).
279  * @exception GeographicErr if there's a problem reading the data; this
280  * never happens if (\e lat, \e lon) is within a successfully cached area.
281  * @return the height of the geoid above the ellipsoid (meters).
282  *
283  * The latitude should be in [&minus;90&deg;, 90&deg;].
284  **********************************************************************/
285  Math::real operator()(real lat, real lon) const {
286  return height(lat, lon);
287  }
288 
289  /**
290  * Convert a height above the geoid to a height above the ellipsoid and
291  * vice versa.
292  *
293  * @param[in] lat latitude of the point (degrees).
294  * @param[in] lon longitude of the point (degrees).
295  * @param[in] h height of the point (degrees).
296  * @param[in] d a Geoid::convertflag specifying the direction of the
297  * conversion; Geoid::GEOIDTOELLIPSOID means convert a height above the
298  * geoid to a height above the ellipsoid; Geoid::ELLIPSOIDTOGEOID means
299  * convert a height above the ellipsoid to a height above the geoid.
300  * @exception GeographicErr if there's a problem reading the data; this
301  * never happens if (\e lat, \e lon) is within a successfully cached area.
302  * @return converted height (meters).
303  **********************************************************************/
304  Math::real ConvertHeight(real lat, real lon, real h,
305  convertflag d) const {
306  return h + real(d) * height(lat, lon);
307  }
308 
309  ///@}
310 
311  /** \name Inspector functions
312  **********************************************************************/
313  ///@{
314  /**
315  * @return geoid description, if available, in the data file; if
316  * absent, return "NONE".
317  **********************************************************************/
318  const std::string& Description() const { return _description; }
319 
320  /**
321  * @return date of the data file; if absent, return "UNKNOWN".
322  **********************************************************************/
323  const std::string& DateTime() const { return _datetime; }
324 
325  /**
326  * @return full file name used to load the geoid data.
327  **********************************************************************/
328  const std::string& GeoidFile() const { return _filename; }
329 
330  /**
331  * @return "name" used to load the geoid data (from the first argument of
332  * the constructor).
333  **********************************************************************/
334  const std::string& GeoidName() const { return _name; }
335 
336  /**
337  * @return directory used to load the geoid data.
338  **********************************************************************/
339  const std::string& GeoidDirectory() const { return _dir; }
340 
341  /**
342  * @return interpolation method ("cubic" or "bilinear").
343  **********************************************************************/
344  const std::string Interpolation() const
345  { return std::string(_cubic ? "cubic" : "bilinear"); }
346 
347  /**
348  * @return estimate of the maximum interpolation and quantization error
349  * (meters).
350  *
351  * This relies on the value being stored in the data file. If the value is
352  * absent, return &minus;1.
353  **********************************************************************/
354  Math::real MaxError() const { return _maxerror; }
355 
356  /**
357  * @return estimate of the RMS interpolation and quantization error
358  * (meters).
359  *
360  * This relies on the value being stored in the data file. If the value is
361  * absent, return &minus;1.
362  **********************************************************************/
363  Math::real RMSError() const { return _rmserror; }
364 
365  /**
366  * @return offset (meters).
367  *
368  * This in used in converting from the pixel values in the data file to
369  * geoid heights.
370  **********************************************************************/
371  Math::real Offset() const { return _offset; }
372 
373  /**
374  * @return scale (meters).
375  *
376  * This in used in converting from the pixel values in the data file to
377  * geoid heights.
378  **********************************************************************/
379  Math::real Scale() const { return _scale; }
380 
381  /**
382  * @return true if the object is constructed to be thread safe.
383  **********************************************************************/
384  bool ThreadSafe() const { return _threadsafe; }
385 
386  /**
387  * @return true if a data cache is active.
388  **********************************************************************/
389  bool Cache() const { return _cache; }
390 
391  /**
392  * @return west edge of the cached area; the cache includes this edge.
393  **********************************************************************/
395  return _cache ? ((_xoffset + (_xsize == _width ? 0 : _cubic)
396  + _width/2) % _width - _width/2) / _rlonres :
397  0;
398  }
399 
400  /**
401  * @return east edge of the cached area; the cache excludes this edge.
402  **********************************************************************/
404  return _cache ?
405  CacheWest() +
406  (_xsize - (_xsize == _width ? 0 : 1 + 2 * _cubic)) / _rlonres :
407  0;
408  }
409 
410  /**
411  * @return north edge of the cached area; the cache includes this edge.
412  **********************************************************************/
414  return _cache ? 90 - (_yoffset + _cubic) / _rlatres : 0;
415  }
416 
417  /**
418  * @return south edge of the cached area; the cache excludes this edge
419  * unless it's the south pole.
420  **********************************************************************/
422  return _cache ? 90 - ( _yoffset + _ysize - 1 - _cubic) / _rlatres : 0;
423  }
424 
425  /**
426  * @return \e a the equatorial radius of the WGS84 ellipsoid (meters).
427  *
428  * (The WGS84 value is returned because the supported geoid models are all
429  * based on this ellipsoid.)
430  **********************************************************************/
432  { return Constants::WGS84_a(); }
433 
434  /**
435  * @return \e f the flattening of the WGS84 ellipsoid.
436  *
437  * (The WGS84 value is returned because the supported geoid models are all
438  * based on this ellipsoid.)
439  **********************************************************************/
441  ///@}
442 
443  /**
444  * @return the default path for geoid data files.
445  *
446  * This is the value of the environment variable GEOGRAPHICLIB_GEOID_PATH,
447  * if set; otherwise, it is $GEOGRAPHICLIB_DATA/geoids if the environment
448  * variable GEOGRAPHICLIB_DATA is set; otherwise, it is a compile-time
449  * default (/usr/local/share/GeographicLib/geoids on non-Windows systems
450  * and C:/ProgramData/GeographicLib/geoids on Windows systems).
451  **********************************************************************/
452  static std::string DefaultGeoidPath();
453 
454  /**
455  * @return the default name for the geoid.
456  *
457  * This is the value of the environment variable GEOGRAPHICLIB_GEOID_NAME,
458  * if set; otherwise, it is "egm96-5". The Geoid class does not use this
459  * function; it is just provided as a convenience for a calling program
460  * when constructing a Geoid object.
461  **********************************************************************/
462  static std::string DefaultGeoidName();
463 
464  };
465 
466 } // namespace GeographicLib
467 
468 #if defined(_MSC_VER)
469 # pragma warning (pop)
470 #endif
471 
472 #endif // GEOGRAPHICLIB_GEOID_HPP
const std::string & GeoidFile() const
Definition: Geoid.hpp:328
Math::real Scale() const
Definition: Geoid.hpp:379
#define GEOGRAPHICLIB_EXPORT
Definition: Constants.hpp:91
Math::real RMSError() const
Definition: Geoid.hpp:363
bool ThreadSafe() const
Definition: Geoid.hpp:384
GeographicLib::Math::real real
Definition: GeodSolve.cpp:31
const std::string Interpolation() const
Definition: Geoid.hpp:344
Math::real Offset() const
Definition: Geoid.hpp:371
const std::string & GeoidName() const
Definition: Geoid.hpp:334
Math::real ConvertHeight(real lat, real lon, real h, convertflag d) const
Definition: Geoid.hpp:304
bool Cache() const
Definition: Geoid.hpp:389
Math::real CacheNorth() const
Definition: Geoid.hpp:413
Math::real MaxError() const
Definition: Geoid.hpp:354
Namespace for GeographicLib.
Definition: Accumulator.cpp:12
const std::string & Description() const
Definition: Geoid.hpp:318
Exception handling for GeographicLib.
Definition: Constants.hpp:389
Math::real CacheSouth() const
Definition: Geoid.hpp:421
Header for GeographicLib::Constants class.
Math::real CacheWest() const
Definition: Geoid.hpp:394
Math::real Flattening() const
Definition: Geoid.hpp:440
const std::string & DateTime() const
Definition: Geoid.hpp:323
const std::string & GeoidDirectory() const
Definition: Geoid.hpp:339
void CacheAll() const
Definition: Geoid.hpp:260
Math::real MajorRadius() const
Definition: Geoid.hpp:431
Math::real CacheEast() const
Definition: Geoid.hpp:403
Math::real operator()(real lat, real lon) const
Definition: Geoid.hpp:285
Looking up the height of the geoid above the ellipsoid.
Definition: Geoid.hpp:82