ATT.h File Reference

LAT Attitude Processing Package. More...

#include <ATT/ATT_msg.h>
#include <PBS/WCT.h>

Typedefs

typedef struct _ATT_Control ATT_Control

Functions

Attitude Processing Control Functions

ATT_Control * ATT_get (void)

Get pointer to attitude processing global handle.

unsigned int ATT_init (ATT_Control *ctl, unsigned int numSecs)

Initialize global attitude processing handle.

unsigned int ATT_exit (ATT_Control *ctl)

Shutdown the attitude processing global handle.

unsigned int ATT_reset (ATT_Control *ctl)

Reset the attitude processing global handle.

unsigned int ATT_update (ATT_Control *ctl, const WCT_time t, const double *Q, const float *W)

Update attitude history list.

unsigned int ATT_lookup (ATT_Control *ctl, const WCT_time t, double *Q)

Lookup attitude information in history list.

unsigned int ATT_range (ATT_Control *ctl, WCT_time *tBottom, WCT_time *tTop)

Get current time range of history list.

unsigned int ATT_xform (ATT_Control *ctl, const WCT_time t, const double *Vl, double *Vj)

Trasform a vector from LAT coordinates to J2000 coordinates.

Vector Utility Functions

void ATT_vec_cart_to_sphr_rad (const double *Vc, double *Vs)

Transform a cartesian vector to spherical (ra,dec) coordinates (radians).

void ATT_vec_cart_to_sphr_deg (const double *Vc, double *Vs)

Transform a cartesian vector to spherical (ra,dec) coordinates (degrees).

double ATT_vec_magnitude (const double *V)

Get a vector magnitude.

void ATT_vec_normalize (double *V)

Normallize a vector.

Quaternion Utility Functions

void ATT_quat_multiply (double *Qr, const double *Qa, const double *Qb)

Multiply two quaternions.

double ATT_quat_magnitude (const double *Q)

Get a quaternion magnitude.

void ATT_quat_normalize (double *Q)

Normallize a quaternion.

void ATT_quat_conjugate (double *Qr, const double *Qa)

Get a quaternion conjugate.

Vector Transform Functions

void ATT_xform_vec_by_quat (double *Ve, const double *Q, const double *Vl)

Tranform vector coordinates from LAT to J2000.

Detailed Description

LAT Attitude Processing Package.

Author:: D.L. Wood

This library contains functions and definitions for manipulating and transforming vectors in LAT instrument body coordinates to vectors in J2000 coordinates. The ultimate goal is to produce a vector in J2000 coordinates (RA, DEC) for any given cartesian vector in LAT local coordinates.

The attitude information is input in the form of an attidude state vector which consists of a:

Timestamp as a 64-bit WCT value
Four element SC-J2000 attitude quaternion
Three element SC angular velocity vector

This information is provided to the LAT from the SC GNC system. The attitude library maintains a short time history of the attitude information to allow for vector transformations at arbitrary times in the recent past. Call the function ATT_update() to inform the attitude processing software of a new message available from the SC.

Typedef Documentation

ATT_Control

The type for the global attitude processing control descriptor.

Function Documentation

unsigned int ATT_exit ( ATT_Control * ctl )

Shutdown the attitude processing global handle.

This releases any global resources allocated in the call to ATT_init().

Parameters:

ctl

A pointer to the ATT global control structure.

Returns:: A ATT MSG code.

References _ATT_Control::check, _ATT_Control::history_head, _ATT_Control::history_list, and _ATT_Control::history_lock.

ATT_Control * ATT_get ( void )

Get pointer to attitude processing global handle.

This function returns a pointer which may be passed as a parameter to the other functions in this library. The function ATT_init() must be called for this pointer before the other library functions are available.

Returns:: A pointer to the global instance of the attitude processing control structure.

unsigned int ATT_init	(	ATT_Control *	ctl,
		unsigned int	numSecs
	)

Initialize global attitude processing handle.

This function initializes the global attitude processing control state.

Parameters:

	ctl	A pointer to the ATT global control structure.
	numSecs	(Obsolete) The number of seconds backwards to maintain in the attitude history list. Starting with ATT package version V1-3-0, this parameter value is is ignored. Instead, the length of the attitude history list is obtained from the ATT_DB/att_data CDM database.

Returns:: A ATT MSG code.

References ATT_MSG_PER_SEC, ATT_reset(), _ATT_Control::check, _ATT_Control::config, configData, _ATT_Control::history_list, _ATT_Control::history_lock, and _ATT_Control::max_entries.

unsigned int ATT_lookup	(	ATT_Control *	ctl,
		const WCT_time	t,
		double *	Q
	)

Lookup attitude information in history list.

This function looks up the information stored for time t in the attitude history list.

Parameters:

	ctl	A pointer to the ATT global control structure.
	t	The timestamp for the attitude information.
	Q	SC-J2000 quaternion for time t is placed here on successful return: Q[0] = q1 (x) Q[1] = q2 (y) Q[2] = q3 (z) Q[3] = q4 (w) .

Returns:: An ATT MSG code.

References ATT_TIME_RNG_LIMIT, _ATT_Control::check, _ATT_Control::cur_entries, _ATT_Control::history_head, _ATT_Control::history_lock, _ATT_History::node, _ATT_History::Q, and _ATT_History::t.

Referenced by ATT_xform().

void ATT_quat_conjugate	(	double *	Qr,
		const double *	Qa
	)

Get a quaternion conjugate.

Returns the conjugate of quaternion Qa in Qr.

Parameters:

	Qa	Input quaternion. Qa[0] = q1 (x) Qa[1] = q2 (y) Qa[2] = q3 (z) Qa[3] = q4 (w)
	Qr	Output conjugate quaternion. Qr[0] = q1 (x) Qr[1] = q2 (y) Qr[2] = q3 (z) Qr[3] = q4 (w)

Referenced by ATT_xform_vec_by_quat().

double ATT_quat_magnitude ( const double * Q )

Get a quaternion magnitude.

Returns the magnitude of quaternion Q.

Parameters:

Q

Input quaternion.
Q[0] = q1 (x)
Q[1] = q2 (y)
Q[2] = q3 (z)
Q[3] = q4 (w)

Returns:: The magnitude of Q.

Referenced by ATT_quat_normalize().

void ATT_quat_multiply	(	double *	Qr,
		const double *	Qa,
		const double *	Qb
	)

Multiply two quaternions.

Multilplies the quaternion Qa by quaternion Qb and stores the result in Qr. Qr = Qb x Qa. This operation is not commutative.

Parameters:

	Qa	Input quaternion. Qa[0] = q1 (x) Qa[1] = q2 (y) Qa[2] = q3 (z) Qa[3] = q4 (w)
	Qb	Input quaternion. Qb[0] = q1 (x) Qb[1] = q2 (y) Qb[2] = q3 (z) Qb[3] = q4 (w)
	Qr	Output quaternion product. Qr[0] = q1 (x) Qr[1] = q2 (y) Qr[2] = q3 (z) Qr[3] = q4 (w)

Referenced by ATT_update(), and ATT_xform_vec_by_quat().

void ATT_quat_normalize ( double * Q )

Normallize a quaternion.

Modifies quaternion Q so that the result has magnitude '1'. This function works in place.

Parameters:

Q

Input quaternion.
Q[0] = q1 (x)
Q[1] = q2 (y)
Q[2] = q3 (z)
Q[3] = q4 (w)

References ATT_quat_magnitude().

unsigned int ATT_range	(	ATT_Control *	ctl,
		WCT_time *	tBottom,
		WCT_time *	tTop
	)

Get current time range of history list.

This function looks up current range of times in the attitude history list.

Parameters:

	ctl	A pointer to the ATT global control structure.
	tBottom	Stores the bottom (earliest) time from the history list.
	tTop	Stores the top (latest) time from the history list.

Returns:: An ATT MSG code.

References _ATT_Control::check, _ATT_Control::cur_entries, _ATT_Control::history_head, _ATT_Control::history_lock, and _ATT_History::t.

unsigned int ATT_reset ( ATT_Control * ctl )

Reset the attitude processing global handle.

This clears the attitude history list current entries and resets the history list to its initial state.

Parameters:

ctl

A pointer to the ATT global control structure.

Returns:: A ATT MSG code.

References _ATT_Control::check, _ATT_Control::cur_entries, _ATT_Control::history_head, _ATT_Control::history_list, _ATT_Control::history_lock, and _ATT_Control::max_entries.

Referenced by ATT_init().

unsigned int ATT_update	(	ATT_Control *	ctl,
		const WCT_time	t,
		const double *	Q,
		const float *	W
	)

Update attitude history list.

This function updates the tail of the attitude history list.

Parameters:

	ctl	A pointer to the ATT global control structure.
	t	The timestamp for the attitude information.
	Q	SC-J2000 quaternion for time t. Q[0] = q1 (x) Q[1] = q2 (y) Q[2] = q3 (z) Q[3] = q4 (w) .
	W	The SC angular velocity vector for time t (units rad/sec). W[0] = wx W[1] = wy W[2] = wz

Returns:: An ATT MSG code.

References ATT_quat_multiply(), _ATT_Control::check, _ATT_Control::config, _ATT_Control::cur_entries, _ATT_Control::history_head, _ATT_Control::history_list, _ATT_Control::history_lock, _ATT_Control::max_entries, _ATT_History::node, _ATT_History::Q, and _ATT_History::t.

void ATT_vec_cart_to_sphr_deg	(	const double *	Vc,
		double *	Vs
	)

Transform a cartesian vector to spherical (ra,dec) coordinates (degrees).

Transforms the vector Vc in (x,y,z) cartesian coordinates into the vector Vs in (ra,dec) spherical coordinates. Vs is returned in degrees.

Parameters:

	Vc	The input vector in cartisian coordinates. Vc[0] = x Vc[1] = y Vc[2] = z
	Vs	The output vector in spherical coordinates. Vs[0] = ra Vs[1] = dec

References M_PI, and vector_2_longlat().

void ATT_vec_cart_to_sphr_rad	(	const double *	Vc,
		double *	Vs
	)

Transform a cartesian vector to spherical (ra,dec) coordinates (radians).

Transforms the vector Vc in (x,y,z) cartesian coordinates into the vector Vs in (ra,dec) spherical coordinates. Vs is returned in radians.

Parameters:

	Vc	The input vector in cartisian coordinates. Vc[0] = x Vc[1] = y Vc[2] = z
	Vs	The output vector in spherical coordinates. Vs[0] = ra Vs[1] = dec

References vector_2_longlat().

double ATT_vec_magnitude ( const double * V )

Get a vector magnitude.

Returns the magnitude of vector V.

Parameters:

V

Input vector.
V[0] = x
V[1] = y
V[2] = z

Returns:: The magnitude of V.

Referenced by ATT_vec_normalize().

void ATT_vec_normalize ( double * V )

Normallize a vector.

Modifies vector V so that the result has magnitude '1'. This function works in place.

Parameters:

V

Input vector.
V[0] = x
V[1] = y
V[2] = z

References ATT_vec_magnitude().

unsigned int ATT_xform	(	ATT_Control *	ctl,
		const WCT_time	t,
		const double *	Vl,
		double *	Vj
	)

Trasform a vector from LAT coordinates to J2000 coordinates.

This function transforms a vector Vl input in LAT instrument coordiates into a vector Vj in J200 coordinates. The timestamp t is used to lookup the attitude information in the global history list. The SC-J2000 quaternion returned by the lookup is then applied to Vl to produce Vj. The timestamp should correspond to the time at which the transform for Vl should be performed.

Parameters:

	ctl	A pointer to the ATT global control structure.
	t	The timestamp for the attitude information.
	Vl	Input vector in LAT coordinates. Vl[0] = x Vl[1] = y Vl[2] = z
	Vj	Output vector in J2000 coordinates. Vj[0] = x Vj[1] = y Vj[2] = z

Returns:: An ATT MSG code.

References ATT_lookup(), ATT_xform_vec_by_quat(), and _ATT_Control::check.

void ATT_xform_vec_by_quat	(	double *	Ve,
		const double *	Q,
		const double *	Vl
	)

Tranform vector coordinates from LAT to J2000.

Performs coordinate transformation on the vector Vl, which is assumed to be a cartiesian vector in LAT instrument local coordinates (SC body coordinates). The information in quaternion Q is used to transform the vector coordinates into J2000 (ECI) coordinates. The resulting vector coordinates are stored in Ve.

Parameters:

	Q	Input quaternion. Q[0] = q1 (x) Q[1] = q2 (y) Q[2] = q3 (z) Q[3] = q4 (w)
	Vl	Input vector in LAT coordinates. Vl[0] = x Vl[1] = y Vl[2] = z
	Ve	Output vector in J2000 coordinates. Ve[0] = x Ve[1] = y Ve[2] = z

References ATT_quat_conjugate(), and ATT_quat_multiply().

Referenced by ATT_xform().


Typedefs
typedef struct _ATT_Control	ATT_Control
Functions
Attitude Processing Control Functions

ATT_Control *	ATT_get (void)
	Get pointer to attitude processing global handle.
unsigned int	ATT_init (ATT_Control *ctl, unsigned int numSecs)
	Initialize global attitude processing handle.
unsigned int	ATT_exit (ATT_Control *ctl)
	Shutdown the attitude processing global handle.
unsigned int	ATT_reset (ATT_Control *ctl)
	Reset the attitude processing global handle.
unsigned int	ATT_update (ATT_Control ctl, const WCT_time t, const double Q, const float *W)
	Update attitude history list.
unsigned int	ATT_lookup (ATT_Control ctl, const WCT_time t, double Q)
	Lookup attitude information in history list.
unsigned int	ATT_range (ATT_Control ctl, WCT_time tBottom, WCT_time *tTop)
	Get current time range of history list.
unsigned int	ATT_xform (ATT_Control ctl, const WCT_time t, const double Vl, double *Vj)
	Trasform a vector from LAT coordinates to J2000 coordinates.
Vector Utility Functions

void	ATT_vec_cart_to_sphr_rad (const double Vc, double Vs)
	Transform a cartesian vector to spherical (ra,dec) coordinates (radians).
void	ATT_vec_cart_to_sphr_deg (const double Vc, double Vs)
	Transform a cartesian vector to spherical (ra,dec) coordinates (degrees).
double	ATT_vec_magnitude (const double *V)
	Get a vector magnitude.
void	ATT_vec_normalize (double *V)
	Normallize a vector.
Quaternion Utility Functions

void	ATT_quat_multiply (double Qr, const double Qa, const double *Qb)
	Multiply two quaternions.
double	ATT_quat_magnitude (const double *Q)
	Get a quaternion magnitude.
void	ATT_quat_normalize (double *Q)
	Normallize a quaternion.
void	ATT_quat_conjugate (double Qr, const double Qa)
	Get a quaternion conjugate.
Vector Transform Functions

void	ATT_xform_vec_by_quat (double Ve, const double Q, const double *Vl)
	Tranform vector coordinates from LAT to J2000.