gps.h File Reference

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Detailed Description

GNSS core 'c' function library: GPS specific functions.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-14

Since:

2005-07-31

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Copyright (c) 2007, refer to 'author' doxygen tags
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Definition in file gps.h.

#include "basictypes.h"

Go to the source code of this file.

Data Structures
struct	GPS_structEphemeris
	A set of satellite orbit parameters that is used to calculate GPS satellite positions and velocities. In the ephemeris structure below, the parameters for computing satellite clock corrections are also included. More...
struct	GPS_structAlmanac
	A limited set of satellite orbit parameters that is used to calculate rough GPS satellite positions and velocities. The parameters for computing rough satellite clock corrections are also included. More...
Functions
void	GPS_ComputeSatelliteClockCorrectionAndDrift (const unsigned short transmission_gpsweek, const double transmission_gpstow, const unsigned short ephem_week, const unsigned toe, const unsigned toc, const double af0, const double af1, const double af2, const double ecc, const double sqrta, const double delta_n, const double m0, const double tgd, const unsigned char mode, double *clock_correction, double *clock_drift)
void	GPS_ComputeSatellitePositionAndVelocity (const unsigned short transmission_gpsweek, const double transmission_gpstow, const unsigned short ephem_week, const unsigned toe, const double m0, const double delta_n, const double ecc, const double sqrta, const double omega0, const double i0, const double w, const double omegadot, const double idot, const double cuc, const double cus, const double crc, const double crs, const double cic, const double cis, const double estimateOfTrueRange, const double estimteOfRangeRate, double *x, double *y, double *z, double *vx, double *vy, double *vz)
void	GPS_ComputeUserToSatelliteRange (const double userX, const double userY, const double userZ, const double satX, const double satY, const double satZ, double *range)
void	GPS_ComputeUserToSatelliteRangeAndRangeRate (const double userX, const double userY, const double userZ, const double userVx, const double userVy, const double userVz, const double satX, const double satY, const double satZ, const double satVx, const double satVy, const double satVz, double *range, double *range_rate)
void	GPS_ComputeSatellitePositionVelocityAzimuthElevationDoppler_BasedOnAlmanacData (const double userX, const double userY, const double userZ, const unsigned short gpsweek, const double gpstow, const double toa, const unsigned short almanac_week, const unsigned short prn, const double ecc, const double i0, const double omegadot, const double sqrta, const double omega0, const double w, const double m0, const double af0, const double af1, double *clock_correction, double *clock_drift, double *satX, double *satY, double *satZ, double *satVx, double *satVy, double *satVz, double *azimuth, double *elevation, double *doppler)
void	GPS_ComputeSatellitePositionVelocityAzimuthElevationDoppler_BasedOnEphmerisData (const double userX, const double userY, const double userZ, const unsigned short gpsweek, const double gpstow, const unsigned short ephem_week, const unsigned toe, const unsigned toc, const double af0, const double af1, const double af2, const double tgd, const double m0, const double delta_n, const double ecc, const double sqrta, const double omega0, const double i0, const double w, const double omegadot, const double idot, const double cuc, const double cus, const double crc, const double crs, const double cic, const double cis, double *clock_correction, double *clock_drift, double *satX, double *satY, double *satZ, double *satVx, double *satVy, double *satVz, double *azimuth, double *elevation, double *doppler)
BOOL	GPS_DecodeRawGPSEphemeris (const unsigned char subframe1[30], const unsigned char subframe2[30], const unsigned char subframe3[30], unsigned short prn, unsigned *tow, unsigned short *iodc, unsigned char *iode, unsigned *toe, unsigned *toc, unsigned short *week, unsigned char *health, unsigned char *alert_flag, unsigned char *anti_spoof, unsigned char *code_on_L2, unsigned char *ura, unsigned char *L2_P_data_flag, unsigned char *fit_interval_flag, unsigned short *age_of_data_offset, double *tgd, double *af2, double *af1, double *af0, double *m0, double *delta_n, double *ecc, double *sqrta, double *omega0, double *i0, double *w, double *omegadot, double *idot, double *cuc, double *cus, double *crc, double *crs, double *cic, double *cis)

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Function Documentation

void GPS_ComputeSatelliteClockCorrectionAndDrift	(	const unsigned short	transmission_gpsweek,
		const double	transmission_gpstow,
		const unsigned short	ephem_week,
		const unsigned	toe,
		const unsigned	toc,
		const double	af0,
		const double	af1,
		const double	af2,
		const double	ecc,
		const double	sqrta,
		const double	delta_n,
		const double	m0,
		const double	tgd,
		const unsigned char	mode,
		double *	clock_correction,
		double *	clock_drift
	)

Computes the satellite clock and clock dirft corrections given the clock model and ephemeris information.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-12

Since:

2005-08-12

Remarks:

(1) The clock correction parameter is sensitive to the polynomial coefficient source which is either ephemeris related from subframe 1 or from the gps almanac (subframes 4,5). The ephemeris parameters have higher precision 22 & 16 vs 11 & 11 bits.
(2) User must compensate for the GPS week rollover

REFERENCES
[1] ICD-GPS-200C, p. 88-101
[2] Teunissen, P. J. G. & A. Kleusberg (editors) (1998). GPS for Geodesy, 2nd Edition. pp. 43-107 [3] Hofmann-Wellenhof, B. & J. Collins (1994). GPS Theory and Practice, 3rd Edition.
Springer-Verlag Wien New York, pp. 43-74
[4] Wong, R.V.C & K.P. Schwarz (1985). Dynamic Positioning with an Integrated GPS-INS. Formulae and Baseline Tests. University of Calgary. UCSE Report #30003. pp. 22

Parameters:

transmission_gpsweek	GPS week when signal was transmit (0-1024+) [weeks]
transmission_gpstow	GPS time of week when signal was transmit [s]
ephem_week	ephemeris: GPS week (0-1024+) [weeks]
toe	ephemeris: time of week [s]
toc	ephemeris: clock reference time of week [s]
af0	ephemeris: polynomial clock correction coefficient [s], Note: parameters from ephemeris preferred vs almanac (22 vs 11 bits)
af1	ephemeris: polynomial clock correction coefficient [s/s], Note: parameters from ephemeris preferred vs almanac (16 vs 11 bits)
af2	ephemeris: polynomial clock correction coefficient [s/s^2]
ecc	ephemeris: eccentricity of satellite orbit []
sqrta	ephemeris: square root of the semi-major axis of orbit [m^(1/2)]
delta_n	ephemeris: mean motion difference from computed value [rad]
m0	ephemeris: mean anomaly at reference time [rad]
tgd	ephemeris: group delay differential between L1 and L2 [s]
mode	0=L1 only, 1=L2 only (see p. 90, ICD-GPS-200C)
clock_correction	satellite clock correction [m]
clock_drift	satellite clock drift correction [m/s]

Definition at line 72 of file gps.c.

void GPS_ComputeSatellitePositionAndVelocity	(	const unsigned short	transmission_gpsweek,
		const double	transmission_gpstow,
		const unsigned short	ephem_week,
		const unsigned	toe,
		const double	m0,
		const double	delta_n,
		const double	ecc,
		const double	sqrta,
		const double	omega0,
		const double	i0,
		const double	w,
		const double	omegadot,
		const double	idot,
		const double	cuc,
		const double	cus,
		const double	crc,
		const double	crs,
		const double	cic,
		const double	cis,
		const double	estimateOfTrueRange,
		const double	estimteOfRangeRate,
		double *	x,
		double *	y,
		double *	z,
		double *	vx,
		double *	vy,
		double *	vz
	)

Computes the satellite position and velocity in WGS84 based on the supplied ephemeris/almanac parameters.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-07-31

Since:

2005-07-31

REFERENCES
[1] ICD-GPS-200C, p. 94-101
[2] Teunissen, P. J. G. & A. Kleusberg (editors) (1998). GPS for Geodesy, 2nd Edition. pp. 43-107
[3] Hofmann-Wellenhof, B. & J. Collins (1994). GPS Theory and Practice, 3rd Edition. Springer-Verlag Wien New York, pp. 43-74
[4] Wong, R.V.C & K.P. Schwarz (1985). Dynamic Positioning with an Integrated GPS-INS. Formulae and Baseline Tests. University of Calgary. UCSE Report #30003. pp. 22

Parameters:

transmission_gpsweek	GPS week when signal was transmit (0-1024+) [weeks]
transmission_gpstow	GPS time of week when signal was transmit [s]
ephem_week	ephemeris: GPS week (0-1024+) [weeks]
toe	ephemeris: time of week [s]
m0	ephemeris: mean anomaly at reference time [rad]
delta_n	ephemeris: mean motion difference from computed value [rad]
ecc	ephemeris: eccentricity []
sqrta	ephemeris: square root of the semi-major axis [m^(1/2)]
omega0	ephemeris: longitude of ascending node of orbit plane at weekly epoch [rad]
i0	ephemeris: inclination angle at reference time [rad]
w	ephemeris: argument of perigee [rad]
omegadot	ephemeris: rate of right ascension [rad/s]
idot	ephemeris: rate of inclination angle [rad/s]
cuc	ephemeris: amplitude of the cosine harmonic correction term to the argument of latitude [rad]
cus	ephemeris: amplitude of the sine harmonic correction term to the argument of latitude [rad]
crc	ephemeris: amplitude of the cosine harmonic correction term to the orbit radius [m]
crs	ephemeris: amplitude of the sine harmonic correction term to the orbit radius [m]
cic	ephemeris: amplitude of the cosine harmonic correction term to the angle of inclination [rad]
cis	ephemeris: amplitude of the sine harmonic correction term to the angle of inclination [rad]
estimateOfTrueRange	best estimate of the signal propagation time (in m) for Sagnac effect compensation [m]
estimteOfRangeRate	best estimate of the true signal Doppler (in m/s) for Sagnac effect compensation [m/s]
x	satellite x [m]
y	satellite y [m]
z	satellite z [m]
vx	satellite velocity x [m/s]
vy	satellite velocity y [m/s]
vz	satellite velocity z [m/s]

Definition at line 151 of file gps.c.

void GPS_ComputeSatellitePositionVelocityAzimuthElevationDoppler_BasedOnAlmanacData	(	const double	userX,
		const double	userY,
		const double	userZ,
		const unsigned short	gpsweek,
		const double	gpstow,
		const double	toa,
		const unsigned short	almanac_week,
		const unsigned short	prn,
		const double	ecc,
		const double	i0,
		const double	omegadot,
		const double	sqrta,
		const double	omega0,
		const double	w,
		const double	m0,
		const double	af0,
		const double	af1,
		double *	clock_correction,
		double *	clock_drift,
		double *	satX,
		double *	satY,
		double *	satZ,
		double *	satVx,
		double *	satVy,
		double *	satVz,
		double *	azimuth,
		double *	elevation,
		double *	doppler
	)

Computes the satellite position and velocity in WGS84 based on almanac data.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-15

Since:

2005-08-15

Remarks:

(1) Assumes L1 for the clock correction mode
(2) This calculation solves for the satellite position at the true GPS time of week specified. It includes compensation for the satellite clock correction and the Saganc effect, which is a function of the user position.

REFERENCES
[1] ICD-GPS-200C

Parameters:

userX	user X position WGS84 ECEF [m]
userY	user Y position WGS84 ECEF [m]
userZ	user Z position WGS84 ECEF [m]
gpsweek	user gps week (0-1024+) [week]
gpstow	user time of week [s]
toa	time of applicability [s]
almanac_week	gps week of almanac (0-1024+) [week]
prn	GPS prn number []
ecc	eccentricity []
i0	orbital inclination at reference time [rad]
omegadot	rate of right ascension [rad/s]
sqrta	square root of the semi-major axis [m^(1/2)]
omega0	longitude of ascending node of orbit plane at weekly epoch [rad]
w	argument of perigee [rad]
m0	mean anomaly at reference time [rad]
af0	polynomial clock correction coefficient (clock bias) [s], Note: parameters from ephemeris preferred vs almanac (22 vs 11 bits)
af1	polynomial clock correction coefficient (clock drift) [s/s], Note: parameters from ephemeris preferred vs almanac (16 vs 11 bits)
clock_correction	clock correction for this satellite for this epoch [m]
clock_drift	clock drift correction for this satellite for this epoch [m/s]
satX	satellite X position WGS84 ECEF [m]
satY	satellite Y position WGS84 ECEF [m]
satZ	satellite Z position WGS84 ECEF [m]
satVx	satellite X velocity WGS84 ECEF [m/s]
satVy	satellite Y velocity WGS84 ECEF [m/s]
satVz	satellite Z velocity WGS84 ECEF [m/s]
azimuth	satelilte azimuth [rad]
elevation	satelilte elevation [rad]
doppler	satellite doppler with respect to the user position [m/s], Note: User must convert to Hz

Definition at line 390 of file gps.c.

void GPS_ComputeSatellitePositionVelocityAzimuthElevationDoppler_BasedOnEphmerisData	(	const double	userX,
		const double	userY,
		const double	userZ,
		const unsigned short	gpsweek,
		const double	gpstow,
		const unsigned short	ephem_week,
		const unsigned	toe,
		const unsigned	toc,
		const double	af0,
		const double	af1,
		const double	af2,
		const double	tgd,
		const double	m0,
		const double	delta_n,
		const double	ecc,
		const double	sqrta,
		const double	omega0,
		const double	i0,
		const double	w,
		const double	omegadot,
		const double	idot,
		const double	cuc,
		const double	cus,
		const double	crc,
		const double	crs,
		const double	cic,
		const double	cis,
		double *	clock_correction,
		double *	clock_drift,
		double *	satX,
		double *	satY,
		double *	satZ,
		double *	satVx,
		double *	satVy,
		double *	satVz,
		double *	azimuth,
		double *	elevation,
		double *	doppler
	)

Computes the satellite position and velocity in WGS84 based on ephemeris data.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-15

Since:

2005-08-15

Remarks:

(1) Assumes L1 for the clock correction mode
(2) This calculation solves for the satellite position at the true GPS time of week specified. It includes compensation for the satellite clock correction and the Saganc effect, which is a function of the user position.
(3) This function can be called with almanac data by inputting the almanac information and zero for the terms not available. toe and toc are the toa in that case.

REFERENCES
[1] ICD-GPS-200C

Parameters:

userX	user X position WGS84 ECEF [m]
userY	user Y position WGS84 ECEF [m]
userZ	user Z position WGS84 ECEF [m]
gpsweek	gps week of signal transmission (0-1024+) [week]
gpstow	time of week of signal transmission (gpstow-psr/c) [s]
ephem_week	ephemeris: GPS week (0-1024+) [weeks]
toe	ephemeris: time of week [s]
toc	ephemeris: clock reference time of week [s]
af0	ephemeris: polynomial clock correction coefficient [s], Note: parameters from ephemeris preferred vs almanac (22 vs 11 bits)
af1	ephemeris: polynomial clock correction coefficient [s/s], Note: parameters from ephemeris preferred vs almanac (16 vs 11 bits)
af2	ephemeris: polynomial clock correction coefficient [s/s^2]
tgd	ephemeris: group delay differential between L1 and L2 [s]
m0	ephemeris: mean anomaly at reference time [rad]
delta_n	ephemeris: mean motion difference from computed value [rad/s]
ecc	ephemeris: eccentricity []
sqrta	ephemeris: square root of the semi-major axis [m^(1/2)]
omega0	ephemeris: longitude of ascending node of orbit plane at weekly epoch [rad]
i0	ephemeris: inclination angle at reference time [rad]
w	ephemeris: argument of perigee [rad]
omegadot	ephemeris: rate of right ascension [rad/s]
idot	ephemeris: rate of inclination angle [rad/s]
cuc	ephemeris: amplitude of the cosine harmonic correction term to the argument of latitude [rad]
cus	ephemeris: amplitude of the sine harmonic correction term to the argument of latitude [rad]
crc	ephemeris: amplitude of the cosine harmonic correction term to the orbit radius [m]
crs	ephemeris: amplitude of the sine harmonic correction term to the orbit radius [m]
cic	ephemeris: amplitude of the cosine harmonic correction term to the angle of inclination [rad]
cis	ephemeris: amplitude of the sine harmonic correction term to the angle of inclination [rad]
clock_correction	clock correction for this satellite for this epoch [m]
clock_drift	clock drift correction for this satellite for this epoch [m/s]
satX	satellite X position WGS84 ECEF [m]
satY	satellite Y position WGS84 ECEF [m]
satZ	satellite Z position WGS84 ECEF [m]
satVx	satellite X velocity WGS84 ECEF [m/s]
satVy	satellite Y velocity WGS84 ECEF [m/s]
satVz	satellite Z velocity WGS84 ECEF [m/s]
azimuth	satelilte azimuth [rad]
elevation	satelilte elevation [rad]
doppler	satellite doppler with respect to the user position [m/s], Note: User must convert to Hz

Definition at line 549 of file gps.c.

void GPS_ComputeUserToSatelliteRange	(	const double	userX,
		const double	userY,
		const double	userZ,
		const double	satX,
		const double	satY,
		const double	satZ,
		double *	range
	)

Computes the user to satellite range given the user and satellite position.

Author:

Glenn D. MacGougan (GDM)

Date:

2006-11-23

Since:

2006-11-23

Parameters:

userX	user X position WGS84 ECEF [m]
userY	user Y position WGS84 ECEF [m]
userZ	user Z position WGS84 ECEF [m]
satX	satellite X position WGS84 ECEF [m]
satY	satellite Y positoin WGS84 ECEF [m]
satZ	satellite Z position WGS84 ECEF [m]
range	user to satellite range [m]

Definition at line 331 of file gps.c.

void GPS_ComputeUserToSatelliteRangeAndRangeRate	(	const double	userX,
		const double	userY,
		const double	userZ,
		const double	userVx,
		const double	userVy,
		const double	userVz,
		const double	satX,
		const double	satY,
		const double	satZ,
		const double	satVx,
		const double	satVy,
		const double	satVz,
		double *	range,
		double *	range_rate
	)

Computes the user to satellite range and range rate given the user and satellite position and velocities.

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-15

Since:

2005-08-15

Parameters:

userX	user X position WGS84 ECEF [m]
userY	user Y position WGS84 ECEF [m]
userZ	user Z position WGS84 ECEF [m]
userVx	user X velocity WGS84 ECEF [m/s]
userVy	user Y velocity WGS84 ECEF [m/s]
userVz	user Z velocity WGS84 ECEF [m/s]
satX	satellite X position WGS84 ECEF [m]
satY	satellite Y positoin WGS84 ECEF [m]
satZ	satellite Z position WGS84 ECEF [m]
satVx	satellite X velocity WGS84 ECEF [m/s]
satVy	satellite Y velocity WGS84 ECEF [m/s]
satVz	satellite Z velocity WGS84 ECEF [m/s]
range	user to satellite range [m]
range_rate	user to satellite range rate [m/s]

Definition at line 354 of file gps.c.

BOOL GPS_DecodeRawGPSEphemeris	(	const unsigned char	subframe1[30],
		const unsigned char	subframe2[30],
		const unsigned char	subframe3[30],
		unsigned short	prn,
		unsigned *	tow,
		unsigned short *	iodc,
		unsigned char *	iode,
		unsigned *	toe,
		unsigned *	toc,
		unsigned short *	week,
		unsigned char *	health,
		unsigned char *	alert_flag,
		unsigned char *	anti_spoof,
		unsigned char *	code_on_L2,
		unsigned char *	ura,
		unsigned char *	L2_P_data_flag,
		unsigned char *	fit_interval_flag,
		unsigned short *	age_of_data_offset,
		double *	tgd,
		double *	af2,
		double *	af1,
		double *	af0,
		double *	m0,
		double *	delta_n,
		double *	ecc,
		double *	sqrta,
		double *	omega0,
		double *	i0,
		double *	w,
		double *	omegadot,
		double *	idot,
		double *	cuc,
		double *	cus,
		double *	crc,
		double *	crs,
		double *	cic,
		double *	cis
	)

Decodes the raw gps ephemeris (note, with the parity bits removed).

Author:

Glenn D. MacGougan (GDM)

Date:

2005-08-15

Since:

2005-08-15

Returns:

TRUE(1) if successful, FALSE(0) otherwise

Remarks:

(1) Parity bits must be removed from the input subframe data
(2) Returns TRUE(1) if data is successfully decoded
(3) Returns FALSE(0) if the subframe id's are incorrect, i.e. must be subframe1, subframe2, subframe3 in that order
(4) Returns FALSE(0) if the iode's are not consistent for all subframes, note 8 LSB bits of the iodc should equal subframe2 and subframe3 iode
(5) Uses IBM PC format byte alignment

REFERENCES
[1] ICD-GPS-200C

code_on_L2

Parameters:

subframe1	subframe 1 data, 30 bytes * 8bits/byte = 240 bits, thus parity bits have been removed
subframe2	subframe 2 data, 30 bytes * 8bits/byte = 240 bits, thus parity bits have been removed
subframe3	subframe 3 data, 30 bytes * 8bits/byte = 240 bits, thus parity bits have been removed
prn	GPS PRN number (helps with debugging)
tow	time of week in subframe1, the time of the leading bit edge of subframe 2 [s]
iodc	10 bit issue of data (clock), 8 LSB bits will match the iode []
iode	8 bit issue of data (ephemeris) []
toe	reference time ephemeris (0-604800) [s]
toc	reference time (clock) (0-604800) [s]
week	10 bit gps week 0-1023 (user must account for week rollover ) [week]
health	6 bit health parameter, 0 if healthy, unhealth othersize [0=healthy]
alert_flag	1 = URA may be worse than indicated [0,1]
anti_spoof	anti-spoof flag from 0=off, 1=on [0,1]
code_on_L2	0=reserved, 1=P code on L2, 2=C/A on L2 [0,1,2]
ura	User Range Accuracy lookup code, 0 is excellent, 15 is use at own risk [0-15], see p. 83 GPSICD200C
L2_P_data_flag	flag indicating if P is on L2 1=true [0,1]
fit_interval_flag	fit interval flag (four hour interval or longer) 0=4 fours, 1=greater [0,1]
age_of_data_offset	age of data offset [s]
tgd	group delay [s]
af2	polynomial clock correction coefficient (rate of clock drift) [s/s^2]
af1	polynomial clock correction coefficient (clock drift) [s/s]
af0	polynomial clock correction coefficient (clock bias) [s]
m0	mean anomaly at reference time [rad]
delta_n	mean motion difference from computed value [rad/s]
ecc	eccentricity []
sqrta	square root of the semi-major axis [m^(1/2)]
omega0	longitude of ascending node of orbit plane at weekly epoch [rad]
i0	inclination angle at reference time [rad]
w	argument of perigee [rad]
omegadot	rate of right ascension [rad/s]
idot	rate of inclination angle [rad/s]
cuc	amplitude of the cosine harmonic correction term to the argument of latitude [rad]
cus	amplitude of the sine harmonic correction term to the argument of latitude [rad]
crc	amplitude of the cosine harmonic correction term to the orbit radius [m]
crs	amplitude of the sine harmonic correction term to the orbit radius [m]
cic	amplitude of the cosine harmonic correction term to the angle of inclination [rad]
cis	amplitude of the sine harmonic correction term to the angle of inclination [rad]

Definition at line 714 of file gps.c.