Looking up the height of the geoid above the ellipsoid. More...
#include <Geoid.hpp>
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enum | convertflag { ELLIPSOIDTOGEOID = -1, NONE = 0, GEOIDTOELLIPSOID = 1 } |
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Setting up the geoid | |
Geoid (const std::string &name, const std::string &path="", bool cubic=true, bool threadsafe=false) | |
void | CacheArea (real south, real west, real north, real east) const |
void | CacheAll () const |
void | CacheClear () const |
Compute geoid heights | |
Math::real | operator() (real lat, real lon) const |
Math::real | ConvertHeight (real lat, real lon, real h, convertflag d) const |
Inspector functions | |
const std::string & | Description () const |
const std::string & | DateTime () const |
const std::string & | GeoidFile () const |
const std::string & | GeoidName () const |
const std::string & | GeoidDirectory () const |
const std::string | Interpolation () const |
Math::real | MaxError () const |
Math::real | RMSError () const |
Math::real | Offset () const |
Math::real | Scale () const |
bool | ThreadSafe () const |
bool | Cache () const |
Math::real | CacheWest () const |
Math::real | CacheEast () const |
Math::real | CacheNorth () const |
Math::real | CacheSouth () const |
Math::real | MajorRadius () const |
Math::real | Flattening () const |
Static Public Member Functions | |
static std::string | DefaultGeoidName () |
static std::string | DefaultGeoidPath () |
Private Types | |
typedef unsigned short | pixel_t |
typedef Math::real | real |
Private Member Functions | |
void | filepos (int ix, int iy) const |
Geoid (const Geoid &) | |
real | height (real lat, real lon) const |
Geoid & | operator= (const Geoid &) |
real | rawval (int ix, int iy) const |
Private Attributes | |
const real | _a |
bool | _cache |
const bool | _cubic |
std::vector< std::vector< pixel_t > > | _data |
unsigned long long | _datastart |
std::string | _datetime |
const real | _degree |
std::string | _description |
std::string | _dir |
const real | _e2 |
const real | _eps |
std::ifstream | _file |
std::string | _filename |
int | _height |
int | _ix |
int | _iy |
real | _maxerror |
std::string | _name |
real | _offset |
real | _rlatres |
real | _rlonres |
real | _rmserror |
real | _scale |
unsigned long long | _swidth |
real | _t [nterms_] |
bool | _threadsafe |
real | _v00 |
real | _v01 |
real | _v10 |
real | _v11 |
int | _width |
int | _xoffset |
int | _xsize |
int | _yoffset |
int | _ysize |
Static Private Attributes | |
static const int | c0_ = 240 |
static const int | c0n_ = 372 |
static const int | c0s_ = 372 |
static const int | c3_ [stencilsize_ *nterms_] |
static const int | c3n_ [stencilsize_ *nterms_] |
static const int | c3s_ [stencilsize_ *nterms_] |
static const unsigned | nterms_ = ((3 + 1) * (3 + 2))/2 |
static const unsigned | pixel_max_ = 0xffffu |
static const unsigned | pixel_size_ = 2 |
static const unsigned | stencilsize_ = 12 |
Looking up the height of the geoid above the ellipsoid.
This class evaluates the height of one of the standard geoids, EGM84, EGM96, or EGM2008 by bilinear or cubic interpolation into a rectangular grid of data. These geoid models are documented in
The geoids are defined in terms of spherical harmonics. However in order to provide a quick and flexible method of evaluating the geoid heights, this class evaluates the height by interpolation into a grid of precomputed values.
The height of the geoid above the ellipsoid, N, is sometimes called the geoid undulation. It can be used to convert a height above the ellipsoid, h, to the corresponding height above the geoid (the orthometric height, roughly the height above mean sea level), H, using the relations
h = N + H; H = −N + h.
See geoid for details of how to install the data sets, the data format, estimates of the interpolation errors, and how to use caching.
This class is typically not thread safe in that a single instantiation cannot be safely used by multiple threads because of the way the object reads the data set and because it maintains a single-cell cache. If multiple threads need to calculate geoid heights they should all construct thread-local instantiations. Alternatively, set the optional threadsafe parameter to true in the constructor. This causes the constructor to read all the data into memory and to turn off the single-cell caching which results in a Geoid object which is thread safe.
Example of use:
GeoidEval is a command-line utility providing access to the functionality of Geoid.
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Flags indicating conversions between heights above the geoid and heights above the ellipsoid.
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Construct a geoid.
[in] | name | the name of the geoid. |
[in] | path | (optional) directory for data file. |
[in] | cubic | (optional) interpolation method; false means bilinear, true (the default) means cubic. |
[in] | threadsafe | (optional), if true, construct a thread safe object. The default is false |
GeographicErr | if the data file cannot be found, is unreadable, or is corrupt. |
GeographicErr | if threadsafe is true but the memory necessary for caching the data can't be allocated. |
The data file is formed by appending ".pgm" to the name. If path is specified (and is non-empty), then the file is loaded from directory, path. Otherwise the path is given by DefaultGeoidPath(). If the threadsafe parameter is true, the data set is read into memory, the data file is closed, and single-cell caching is turned off; this results in a Geoid object which is thread safe.
Definition at line 200 of file src/Geoid.cpp.
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Cache all the data.
GeographicErr | if the memory necessary for caching the data can't be allocated (in this case, you will have no cache and can try again with a smaller area). |
GeographicErr | if there's a problem reading the data. |
GeographicErr | if this is called on a threadsafe Geoid. |
On most computers, this is fast for data sets with grid resolution of 5' or coarser. For a 1' grid, the required RAM is 450MB; a 2.5' grid needs 72MB; and a 5' grid needs 18MB.
Set up a cache.
[in] | south | latitude (degrees) of the south edge of the cached area. |
[in] | west | longitude (degrees) of the west edge of the cached area. |
[in] | north | latitude (degrees) of the north edge of the cached area. |
[in] | east | longitude (degrees) of the east edge of the cached area. |
GeographicErr | if the memory necessary for caching the data can't be allocated (in this case, you will have no cache and can try again with a smaller area). |
GeographicErr | if there's a problem reading the data. |
GeographicErr | if this is called on a threadsafe Geoid. |
Cache the data for the specified "rectangular" area bounded by the parallels south and north and the meridians west and east. east is always interpreted as being east of west, if necessary by adding 360° to its value. south and north should be in the range [−90°, 90°].
Definition at line 407 of file src/Geoid.cpp.
void GeographicLib::Geoid::CacheClear | ( | ) | const |
Clear the cache. This never throws an error. (This does nothing with a thread safe Geoid.)
Definition at line 394 of file src/Geoid.cpp.
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Convert a height above the geoid to a height above the ellipsoid and vice versa.
[in] | lat | latitude of the point (degrees). |
[in] | lon | longitude of the point (degrees). |
[in] | h | height of the point (degrees). |
[in] | d | a Geoid::convertflag specifying the direction of the conversion; Geoid::GEOIDTOELLIPSOID means convert a height above the geoid to a height above the ellipsoid; Geoid::ELLIPSOIDTOGEOID means convert a height above the ellipsoid to a height above the geoid. |
GeographicErr | if there's a problem reading the data; this never happens if (lat, lon) is within a successfully cached area. |
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This is the value of the environment variable GEOGRAPHICLIB_GEOID_NAME, if set; otherwise, it is "egm96-5". The Geoid class does not use this function; it is just provided as a convenience for a calling program when constructing a Geoid object.
Definition at line 501 of file src/Geoid.cpp.
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This is the value of the environment variable GEOGRAPHICLIB_GEOID_PATH, if set; otherwise, it is $GEOGRAPHICLIB_DATA/geoids if the environment variable GEOGRAPHICLIB_DATA is set; otherwise, it is a compile-time default (/usr/local/share/GeographicLib/geoids on non-Windows systems and C:/ProgramData/GeographicLib/geoids on Windows systems).
Definition at line 488 of file src/Geoid.cpp.
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Definition at line 306 of file src/Geoid.cpp.
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Compute the geoid height at a point
[in] | lat | latitude of the point (degrees). |
[in] | lon | longitude of the point (degrees). |
GeographicErr | if there's a problem reading the data; this never happens if (lat, lon) is within a successfully cached area. |
The latitude should be in [−90°, 90°].
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