#include <FGLocation.h>
Inherits FGJSBBase.
This class provides access functions to set and get the location as either the simple x, y and z values in ft or longitude/latitude and the radial distance of the location from the earth center.
It is common to associate a parent frame with a location. This frame is usually called the local horizontal frame or simply the local frame. This frame has its x/y plane parallel to the surface of the earth (with the assumption of a spherical earth). The x-axis points towards north, the y-axis points towards east and the z-axis points to the center of the earth.
Since this frame is determined by the location, this class also provides the rotation matrices required to transform from the earth centered frame to the local horizontal frame and back. There are also conversion functions for conversion of position vectors given in the one frame to positions in the other frame.
The earth centered reference frame is *NOT* an inertial frame since it rotates with the earth.
The coordinates in the earth centered frame are the master values. All other values are computed from these master values and are cached as long as the location is changed by access through a non-const member function. Values are cached to improve performance. It is best practice to work with a natural set of master values. Other parameters that are derived from these master values are calculated only when needed, and IF they are needed and calculated, then they are cached (stored and remembered) so they do not need to be re-calculated until the master values they are derived from are themselves changed (and become stale).
Accuracy and round off:
Given that we model a vehicle near the earth, the earths surface radius is about 2*10^7, ft and that we use double values for the representation of the location, we have an accuracy of about 1e-16*2e7ft/1=2e-9ft left. This should be sufficient for our needs. Note that this is the same relative accuracy we would have when we compute directly with lon/lat/radius. For the radius value this is clear. For the lon/lat pair this is easy to see. Take for example KSFO located at about 37.61deg north 122.35deg west, which corresponds to 0.65642rad north and 2.13541rad west. Both values are of magnitude of about 1. But 1ft corresponds to about 1/(2e7*2*pi)=7.9577e-09rad. So the left accuracy with this representation is also about 1*1e-16/7.9577e-09=1.2566e-08 which is of the same magnitude as the representation chosen here.
The advantage of this representation is that it is a linear space without singularities. The singularities are the north and south pole and most notably the non-steady jump at -pi to pi. It is harder to track this jump correctly especially when we need to work with error norms and derivatives of the equations of motion within the time-stepping code. Also, the rate of change is of the same magnitude for all components in this representation which is an advantage for numerical stability in implicit time-stepping too.
Note: The latitude is a GEOCENTRIC value. FlightGear converts latitude to a geodetic value and uses that. In order to get best matching relative to a map, geocentric latitude must be converted to geodetic.
W. C. Durham "Aircraft Dynamics & Control", section 2.2
Definition at line 142 of file FGLocation.h.
Public Member Functions | |
| double & | Entry (unsigned int idx) |
| Write access the entries of the vector. | |
| double | Entry (unsigned int idx) const |
| Read access the entries of the vector. | |
| FGLocation (const FGLocation &l) | |
| Copy constructor. | |
| FGLocation (const FGColumnVector3 &lv) | |
| Column constructor. | |
| FGLocation (double lon, double lat, double radius) | |
| Constructor to set the longitude, latitude and the distance from the center of the earth. | |
| FGLocation (void) | |
| Default constructor. | |
| double | GetCosLatitude () const |
| Get the cosine of Latitude. | |
| double | GetCosLongitude () const |
| Get the cosine of Longitude. | |
| double | GetGeodAltitude (void) const |
| Gets the geodetic altitude in feet. | |
| double | GetGeodLatitudeDeg (void) const |
| Get the geodetic latitude in degrees. | |
| double | GetGeodLatitudeRad (void) const |
| Get the geodetic latitude. | |
| double | GetLatitude () const |
| Get the latitude. | |
| double | GetLatitudeDeg () const |
| Get the latitude. | |
| double | GetLongitude () const |
| Get the longitude. | |
| double | GetLongitudeDeg () const |
| Get the longitude. | |
| double | GetRadius () const |
| Get the distance from the center of the earth. | |
| double | GetSinLatitude () const |
| Get the sine of Latitude. | |
| double | GetSinLongitude () const |
| Get the sine of Longitude. | |
| double | GetTanLatitude () const |
| Get the cosine of Latitude. | |
| const FGMatrix33 & | GetTec2i (double epa) |
| Transform matrix from the earth centered to inertial frame. | |
| const FGMatrix33 & | GetTec2l (void) const |
| Transform matrix from the earth centered to local horizontal frame. | |
| const FGMatrix33 & | GetTi2ec (double epa) |
| Transform matrix from inertial to earth centered frame. | |
| const FGMatrix33 & | GetTl2ec (void) const |
| Transform matrix from local horizontal to earth centered frame. | |
| FGLocation | LocalToLocation (const FGColumnVector3 &lvec) const |
| Conversion from Local frame coordinates to a location in the earth centered and fixed frame. | |
| FGColumnVector3 | LocationToLocal (const FGColumnVector3 &ecvec) const |
| Conversion from a location in the earth centered and fixed frame to local horizontal frame coordinates. | |
| operator const FGColumnVector3 & () const | |
| Cast to a simple 3d vector. | |
| bool | operator!= (const FGLocation &l) const |
| double & | operator() (unsigned int idx) |
| Write access the entries of the vector. | |
| double | operator() (unsigned int idx) const |
| Read access the entries of the vector. | |
| FGLocation | operator* (double scalar) const |
| const FGLocation & | operator*= (double scalar) |
| FGLocation | operator+ (const FGLocation &l) const |
| const FGLocation & | operator+= (const FGLocation &l) |
| FGLocation | operator- (const FGLocation &l) const |
| const FGLocation & | operator-= (const FGLocation &l) |
| const FGLocation & | operator/= (double scalar) |
| const FGLocation & | operator= (const FGLocation &l) |
| const FGLocation & | operator= (const FGColumnVector3 &v) |
| bool | operator== (const FGLocation &l) const |
| void | SetEllipse (double semimajor, double semiminor) |
| Sets the semimajor and semiminor axis lengths for this planet. | |
| void | SetLatitude (double latitude) |
| Set the latitude. | |
| void | SetLongitude (double longitude) |
| Set the longitude. | |
| void | SetPosition (double lon, double lat, double radius) |
| Sets the longitude, latitude and the distance from the center of the earth. | |
| void | SetRadius (double radius) |
| Set the distance from the center of the earth. | |
| FGLocation | ( | void | ) |
Definition at line 55 of file FGLocation.cpp.
| FGLocation | ( | double | lon, | |
| double | lat, | |||
| double | radius | |||
| ) |
| lon | longitude | |
| lat | GEOCENTRIC latitude | |
| radius | distance from center of earth to vehicle in feet |
Definition at line 71 of file FGLocation.cpp.
| FGLocation | ( | const FGColumnVector3 & | lv | ) | [inline] |
Definition at line 156 of file FGLocation.h.
| FGLocation | ( | const FGLocation & | l | ) | [inline] |
Definition at line 169 of file FGLocation.h.
| double& Entry | ( | unsigned int | idx | ) | [inline] |
| idx | the component index. |
Definition at line 378 of file FGLocation.h.
| double Entry | ( | unsigned int | idx | ) | const [inline] |
| idx | the component index. |
double operator()(unsigned int idx) const function. It is used internally to access the elements in a more convenient way. Note that the index given in the argument is unchecked. Definition at line 368 of file FGLocation.h.
| double GetCosLatitude | ( | ) | const [inline] |
Definition at line 290 of file FGLocation.h.
| double GetCosLongitude | ( | ) | const [inline] |
Definition at line 257 of file FGLocation.h.
| double GetGeodAltitude | ( | void | ) | const [inline] |
Definition at line 284 of file FGLocation.h.
| double GetGeodLatitudeDeg | ( | void | ) | const [inline] |
Definition at line 281 of file FGLocation.h.
| double GetGeodLatitudeRad | ( | void | ) | const [inline] |
Definition at line 269 of file FGLocation.h.
| double GetLatitude | ( | void | ) | const [inline] |
Definition at line 263 of file FGLocation.h.
| double GetLatitudeDeg | ( | void | ) | const [inline] |
Definition at line 275 of file FGLocation.h.
| double GetLongitude | ( | void | ) | const [inline] |
Definition at line 245 of file FGLocation.h.
| double GetLongitudeDeg | ( | void | ) | const [inline] |
Definition at line 251 of file FGLocation.h.
| double GetRadius | ( | void | ) | const [inline] |
Definition at line 306 of file FGLocation.h.
| double GetSinLatitude | ( | ) | const [inline] |
Definition at line 287 of file FGLocation.h.
| double GetSinLongitude | ( | ) | const [inline] |
Definition at line 254 of file FGLocation.h.
| double GetTanLatitude | ( | ) | const [inline] |
Definition at line 293 of file FGLocation.h.
| const FGMatrix33 & GetTec2i | ( | double | epa | ) |
Returns a const reference to the rotation matrix of the transform from the earth centered frame to the inertial frame (ECEF to ECI).
Definition at line 189 of file FGLocation.cpp.
| const FGMatrix33& GetTec2l | ( | void | ) | const [inline] |
Returns a const reference to the rotation matrix of the transform from the earth centered frame to the local horizontal frame.
Definition at line 316 of file FGLocation.h.
| const FGMatrix33 & GetTi2ec | ( | double | epa | ) |
Returns a const reference to the rotation matrix of the transform from the inertial frame to the earth centered frame (ECI to ECEF).
Definition at line 200 of file FGLocation.cpp.
| const FGMatrix33& GetTl2ec | ( | void | ) | const [inline] |
Returns a const reference to the rotation matrix of the transform from the local horizontal frame to the earth centered frame.
Definition at line 311 of file FGLocation.h.
| FGLocation LocalToLocation | ( | const FGColumnVector3 & | lvec | ) | const [inline] |
| lvec | Vector in the local horizontal coordinate frame |
Definition at line 332 of file FGLocation.h.
| FGColumnVector3 LocationToLocal | ( | const FGColumnVector3 & | ecvec | ) | const [inline] |
| ecvec | Vector in the earth centered and fixed frame |
Definition at line 340 of file FGLocation.h.
| double& operator() | ( | unsigned int | idx | ) | [inline] |
| idx | the component index. |
Definition at line 358 of file FGLocation.h.
| double operator() | ( | unsigned int | idx | ) | const [inline] |
| idx | the component index. Return the value of the matrix entry at the given index. Indices are counted starting with 1. Note that the index given in the argument is unchecked. |
Definition at line 351 of file FGLocation.h.
| void SetEllipse | ( | double | semimajor, | |
| double | semiminor | |||
| ) |
The eccentricity and flattening are calculated from the semimajor and semiminor axis lengths
Definition at line 171 of file FGLocation.cpp.
| void SetLatitude | ( | double | latitude | ) |
| latitude | Latitude in rad to set. Sets the latitude of the location represented with this class instance to the value of the given argument. The value is meant to be in rad. The longitude and the radius value are preserved with this call with the exception of radius being equal to zero. If the radius is previously set to zero it is changed to be equal to 1.0 past this call. Latitude is positive north and negative south. The arguments should be within the bounds of -pi/2 <= lat <= pi/2. The behavior of this function with arguments outside this range is left as an exercise to the gentle reader ... |
Definition at line 117 of file FGLocation.cpp.
| void SetLongitude | ( | double | longitude | ) |
| longitude | Longitude in rad to set. Sets the longitude of the location represented with this class instance to the value of the given argument. The value is meant to be in rad. The latitude and the radius value are preserved with this call with the exception of radius being equal to zero. If the radius is previously set to zero it is changed to be equal to 1.0 past this call. Longitude is positive east and negative west. |
Definition at line 95 of file FGLocation.cpp.
| void SetPosition | ( | double | lon, | |
| double | lat, | |||
| double | radius | |||
| ) |
| lon | longitude in radians | |
| lat | GEOCENTRIC latitude in radians | |
| radius | distance from center of earth to vehicle in feet |
Definition at line 154 of file FGLocation.cpp.
| void SetRadius | ( | double | radius | ) |
| radius | Radius in ft to set. Sets the radius of the location represented with this class instance to the value of the given argument. The value is meant to be in ft. The latitude and longitude values are preserved with this call with the exception of radius being equal to zero. If the radius is previously set to zero, latitude and longitude is set equal to zero past this call. The argument should be positive. The behavior of this function called with a negative argument is left as an exercise to the gentle reader ... |
Definition at line 141 of file FGLocation.cpp.
1.5.5