ckw01_c |

Table of contents## Procedureckw01_c ( C-Kernel, write segment to C-kernel, data type 1 ) void ckw01_c ( SpiceInt handle, SpiceDouble begtim, SpiceDouble endtim, SpiceInt inst, ConstSpiceChar * ref, SpiceBoolean avflag, ConstSpiceChar * segid, SpiceInt nrec, ConstSpiceDouble sclkdp [], ConstSpiceDouble quats [][4], ConstSpiceDouble avvs [][3] ) ## AbstractAdd a type 1 segment to a C-kernel. ## Required_ReadingCK DAF SCLK ## KeywordsPOINTING UTILITY ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- handle I Handle of an open CK file. begtim I The beginning encoded SCLK of the segment. endtim I The ending encoded SCLK of the segment. inst I The NAIF instrument ID code. ref I The reference frame of the segment. avflag I SPICETRUE if the segment will contain angular velocity. segid I Segment identifier. nrec I Number of pointing records. sclkdp I Encoded SCLK times. quats I Quaternions representing instrument pointing. avvs I Angular velocity vectors. ## Detailed_Inputhandle is the handle of the CK file to which the segment will be written. The file must have been opened with write access. begtim is the beginning encoded SCLK time of the segment. This value should be less than or equal to the first time in the segment. endtim is the encoded SCLK time at which the segment ends. This value should be greater than or equal to the last time in the segment. inst is the NAIF integer ID code for the instrument. ref is a character string which specifies the reference frame of the segment. This should be one of the frames supported by the SPICELIB routine NAMFRM which is an entry point of FRAMEX. avflag is a logical flag which indicates whether or not the segment will contain angular velocity. segid is the segment identifier. A CK segment identifier may contain up to 40 characters, excluding the terminating null. nrec is the number of pointing instances in the segment. sclkdp are the encoded spacecraft clock times associated with each pointing instance. These times must be strictly increasing. quats is an array of SPICE-style quaternions representing a sequence of C-matrices. See the discussion of "Quaternion Styles" in the -Particulars section below. avvs are the angular velocity vectors (optional). If avflag is SPICEFALSE then this array is ignored by the routine, however it still must be supplied as part of the calling sequence. ## Detailed_OutputNone. See -Files section. ## ParametersNone. ## Exceptions1) If `handle' is not the handle of a C-kernel opened for writing, an error is signaled by a routine in the call tree of this routine. 2) If `segid' is more than 40 characters long, the error SPICE(SEGIDTOOLONG) is signaled by a routine in the call tree of this routine. 3) If `segid' contains any nonprintable characters, the error SPICE(NONPRINTABLECHARS) is signaled by a routine in the call tree of this routine. 4) If the first encoded SCLK time is negative, the error SPICE(INVALIDSCLKTIME) is signaled by a routine in the call tree of this routine. 5) If the second encoded SCLK or any subsequent times, or if the encoded SCLK times are not strictly increasing, the error SPICE(TIMESOUTOFORDER) is signaled by a routine in the call tree of this routine. 6) If `begtim' is greater than sclkdp[0] or `endtim' is less than sclkdp[nrec-1], the error SPICE(INVALIDDESCRTIME) is signaled by a routine in the call tree of this routine. 7) If the name of the reference frame is not one of those supported by the routine namfrm_c, the error SPICE(INVALIDREFFRAME) is signaled by a routine in the call tree of this routine. 8) If `nrec', the number of pointing records, is less than or equal to 0, the error SPICE(INVALIDNUMREC) is signaled by a routine in the call tree of this routine. 9) If any quaternion has magnitude zero, the error SPICE(ZEROQUATERNION) is signaled by a routine in the call tree of this routine. 10) If any of the `ref' or `segid' input string pointers is null, the error SPICE(NULLPOINTER) is signaled. 11) If any of the `ref' or `segid' input strings has zero length, the error SPICE(EMPTYSTRING) is signaled. ## FilesThis routine adds a type 1 segment to a C-kernel. The C-kernel may be either a new one or an existing one opened for writing. ## ParticularsFor a detailed description of a type 1 CK segment please see the CK Required Reading. This routine relieves the user from performing the repetitive calls to the DAF routines necessary to construct a CK segment. Quaternion Styles ----------------- There are different "styles" of quaternions used in science and engineering applications. Quaternion styles are characterized by - The order of quaternion elements - The quaternion multiplication formula - The convention for associating quaternions with rotation matrices Two of the commonly used styles are - "SPICE" > Invented by Sir William Rowan Hamilton > Frequently used in mathematics and physics textbooks - "Engineering" > Widely used in aerospace engineering applications CSPICE function interfaces ALWAYS use SPICE quaternions. Quaternions of any other style must be converted to SPICE quaternions before they are passed to CSPICE functions. Relationship between SPICE and Engineering Quaternions ------------------------------------------------------ Let M be a rotation matrix such that for any vector V, M*V is the result of rotating V by theta radians in the counterclockwise direction about unit rotation axis vector A. Then the SPICE quaternions representing M are (+/-) ( cos(theta/2), sin(theta/2) A(1), sin(theta/2) A(2), sin(theta/2) A(3) ) while the engineering quaternions representing M are (+/-) ( -sin(theta/2) A(1), -sin(theta/2) A(2), -sin(theta/2) A(3), cos(theta/2) ) For both styles of quaternions, if a quaternion q represents a rotation matrix M, then -q represents M as well. Given an engineering quaternion QENG = ( q0, q1, q2, q3 ) the equivalent SPICE quaternion is QSPICE = ( q3, -q0, -q1, -q2 ) Associating SPICE Quaternions with Rotation Matrices ---------------------------------------------------- Let FROM and TO be two right-handed reference frames, for example, an inertial frame and a spacecraft-fixed frame. Let the symbols V , V FROM TO denote, respectively, an arbitrary vector expressed relative to the FROM and TO frames. Let M denote the transformation matrix that transforms vectors from frame FROM to frame TO; then V = M * V TO FROM where the expression on the right hand side represents left multiplication of the vector by the matrix. Then if the unit-length SPICE quaternion q represents M, where q = (q0, q1, q2, q3) the elements of M are derived from the elements of q as follows: .- -. | 2 2 | | 1 - 2*( q2 + q3 ) 2*(q1*q2 - q0*q3) 2*(q1*q3 + q0*q2) | | | | | | 2 2 | M = | 2*(q1*q2 + q0*q3) 1 - 2*( q1 + q3 ) 2*(q2*q3 - q0*q1) | | | | | | 2 2 | | 2*(q1*q3 - q0*q2) 2*(q2*q3 + q0*q1) 1 - 2*( q1 + q2 ) | | | `- -' Note that substituting the elements of -q for those of q in the right hand side leaves each element of M unchanged; this shows that if a quaternion q represents a matrix M, then so does the quaternion -q. To map the rotation matrix M to a unit quaternion, we start by decomposing the rotation matrix as a sum of symmetric and skew-symmetric parts: 2 M = [ I + (1-cos(theta)) OMEGA ] + [ sin(theta) OMEGA ] symmetric skew-symmetric OMEGA is a skew-symmetric matrix of the form .- -. | 0 -n3 n2 | | | OMEGA = | n3 0 -n1 | | | | -n2 n1 0 | `- -' The vector N of matrix entries (n1, n2, n3) is the rotation axis of M and theta is M's rotation angle. Note that N and theta are not unique. Let C = cos(theta/2) S = sin(theta/2) Then the unit quaternions Q corresponding to M are Q = +/- ( C, S*n1, S*n2, S*n3 ) The mappings between quaternions and the corresponding rotations are carried out by the CSPICE routines q2m_c {quaternion to matrix} m2q_c {matrix to quaternion} m2q_c always returns a quaternion with scalar part greater than or equal to zero. SPICE Quaternion Multiplication Formula --------------------------------------- Given a SPICE quaternion Q = ( q0, q1, q2, q3 ) corresponding to rotation axis A and angle theta as above, we can represent Q using "scalar + vector" notation as follows: s = q0 = cos(theta/2) v = ( q1, q2, q3 ) = sin(theta/2) * A Q = s + v Let Q1 and Q2 be SPICE quaternions with respective scalar and vector parts s1, s2 and v1, v2: Q1 = s1 + v1 Q2 = s2 + v2 We represent the dot product of v1 and v2 by <v1, v2> and the cross product of v1 and v2 by v1 x v2 Then the SPICE quaternion product is Q1*Q2 = s1*s2 - <v1,v2> + s1*v2 + s2*v1 + (v1 x v2) If Q1 and Q2 represent the rotation matrices M1 and M2 respectively, then the quaternion product Q1*Q2 represents the matrix product M1*M2 ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) The following example creates a CK file with a type 1 segment from a series of pointing instances that represent a structure initially aligned with the J2000 frame, and which is rotating about the J2000 Z-axis. There will be one pointing instance per 10-tick interval. Example code begins here. /. Program ckw01_ex1 ./ #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define CK1 "ckw01_ex1.bc" #define SPTICK 0.001 #define INST -77701 #define MAXREC 201 /. Local variables. ./ SpiceChar * ref; SpiceChar * ifname; SpiceChar * segid; SpiceDouble avvs [MAXREC][3]; SpiceDouble begtim; SpiceDouble endtim; SpiceDouble quats [MAXREC][4]; SpiceDouble rate; SpiceDouble rwmat [3][3]; SpiceDouble sclkdp [MAXREC]; SpiceDouble spaces; SpiceDouble sticks; SpiceDouble theta; SpiceDouble wmat [3][3]; SpiceDouble wquat [4]; SpiceInt handle; SpiceInt i; SpiceInt ncomch; SpiceBoolean avflag; /. `ncomch' is the number of characters to reserve for the kernel's comment area. This example doesn't write comments, so set to zero. ./ ncomch = 0; /. The base reference from for the rotation data. ./ ref = "J2000"; /. Time spacing in encoded ticks and in seconds ./ sticks = 10.0; spaces = sticks * SPTICK; /. Declare an angular rate in radians per sec. ./ rate = 1.e-2; /. Internal file name and segment ID. ./ segid = "Test type 1 CK segment"; ifname = "Test CK type 1 segment created by ## RestrictionsNone. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) ## Version-CSPICE Version 2.0.1, 10-AUG-2021 (JDR) Edited the header to comply with NAIF standard. Created complete code example from existing fragment. -CSPICE Version 2.0.0, 01-JUN-2010 (NJB) The check for non-unit quaternions has been replaced with a check for zero-length quaternions. (The implementation of the check is located in ckw01_.) -CSPICE Version 1.3.2, 27-FEB-2008 (NJB) Updated header; added information about SPICE quaternion conventions. -CSPICE Version 1.3.1, 12-JUN-2006 (NJB) Corrected typo in example, the SCLK indexes for the begtim and endtim assignments used FORTRAN convention. -CSPICE Version 1.3.0, 28-AUG-2001 (NJB) Changed prototype: inputs sclkdp, quats, and avvs are now const-qualified. Implemented interface macros for casting these inputs to const. -CSPICE Version 1.2.0, 02-SEP-1999 (NJB) Local type logical variable now used for angular velocity flag used in interface of ckw01_. -CSPICE Version 1.1.0, 08-FEB-1998 (NJB) References to C2F_CreateStr_Sig were removed; code was cleaned up accordingly. String checks are now done using the macro CHKFSTR. -CSPICE Version 1.0.0, 25-OCT-1997 (NJB) Based on SPICELIB Version 2.0.0, 28-DEC-1993 (WLT) ## Index_Entrieswrite CK type_1 pointing data segment |

Fri Dec 31 18:41:02 2021