spkw20 |
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ProcedureSPKW20 ( SPK, write segment, type 20 ) SUBROUTINE SPKW20 ( HANDLE, BODY, CENTER, FRAME, . FIRST, LAST, SEGID, INTLEN, . N, POLYDG, CDATA, DSCALE, . TSCALE, INITJD, INITFR ) AbstractWrite a type 20 segment to an SPK file. Required_ReadingDAF NAIF_IDS TIME SPK KeywordsEPHEMERIS DeclarationsIMPLICIT NONE INCLUDE 'spk20.inc' INTEGER HANDLE INTEGER BODY INTEGER CENTER CHARACTER*(*) FRAME DOUBLE PRECISION FIRST DOUBLE PRECISION LAST CHARACTER*(*) SEGID DOUBLE PRECISION INTLEN INTEGER N INTEGER POLYDG DOUBLE PRECISION CDATA ( * ) DOUBLE PRECISION DSCALE DOUBLE PRECISION TSCALE DOUBLE PRECISION INITJD DOUBLE PRECISION INITFR Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- HANDLE I Handle of SPK file open for writing. BODY I NAIF code for ephemeris object. CENTER I NAIF code for the center of motion of the body. FRAME I Reference frame name. FIRST I Start time of interval covered by segment. LAST I End time of interval covered by segment. SEGID I Segment identifier. INTLEN I Length of time covered by logical record (days). N I Number of logical records in segment. POLYDG I Chebyshev polynomial degree. CDATA I Array of Chebyshev coefficients and positions. DSCALE I Distance scale of data. TSCALE I Time scale of data. INITJD I Integer part of begin time (TDB Julian date) of first record. INITFR I Fractional part of begin time of first record. Detailed_InputHANDLE is the DAF handle of an SPK file to which a type 20 segment is to be added. The SPK file must be open for writing. BODY is the NAIF integer code for an ephemeris object whose state relative to another body is described by the segment to be created. CENTER is the NAIF integer code for the center of motion of the object identified by BODY. FRAME is the NAIF name for a reference frame relative to which the state information for BODY is specified. FIRST, LAST are the start and stop times of the time interval over which the segment defines the state of the object identified by BODY. SEGID is a segment identifier. An SPK segment identifier may contain up to 40 characters. INTLEN is the length of time, in TDB Julian days, covered by each set of Chebyshev polynomial coefficients (each logical record). N is the number of logical records to be stored in the segment. There is one logical record for each time period. Each logical record contains three sets of Chebyshev coefficients---one for each coordinate---and three position vector components. POLYDG is the degree of each set of Chebyshev polynomials, i.e. the number of Chebyshev coefficients per coordinate minus one. POLYDG must be less than or equal to the parameter MAXDEG. CDATA is an array containing all the sets of Chebyshev polynomial coefficients and position components to be placed in the new segment of the SPK file. There are three sets of coefficients and position components for each time interval covered by the segment. The coefficients and position components are stored in CDATA in order as follows: the (POLYDG + 1) coefficients for the first coordinate of the first logical record, followed by the X component of position at the first interval midpoint. The first coefficient is that of the constant term of the expansion. the coefficients for the second coordinate, followed by the Y component of position at the first interval midpoint. the coefficients for the third coordinate, followed by the Z component of position at the first interval midpoint. the coefficients for the first coordinate for the second logical record, followed by the X component of position at the second interval midpoint. and so on. The logical data records are stored contiguously: +----------+ | Record 1 | +----------+ | Record 2 | +----------+ ... +----------+ | Record N | +----------+ The contents of an individual record are: +--------------------------------------+ | Coeff set for X velocity component | +--------------------------------------+ | X position component | +--------------------------------------+ | Coeff set for Y velocity component | +--------------------------------------+ | Y position component | +--------------------------------------+ | Coeff set for Z velocity component | +--------------------------------------+ | Z position component | +--------------------------------------+ Each coefficient set has the structure: +--------------------------------------+ | Coefficient of T_0 | +--------------------------------------+ | Coefficient of T_1 | +--------------------------------------+ ... +--------------------------------------+ | Coefficient of T_POLYDG | +--------------------------------------+ Where T_n represents the Chebyshev polynomial of the first kind of degree n. DSCALE, TSCALE are, respectively, the distance scale of the input position and velocity data in km, and the time scale of the input velocity data in TDB seconds. For example, if the input distance data have units of astronomical units (AU), DSCALE should be set to the number of km in one AU. If the input velocity data have time units of Julian days, then TSCALE should be set to the number of seconds per Julian day (86400). INITJD is the integer part of the Julian ephemeris date of initial epoch of the first record. INITJD may be less than, equal to, or greater than the initial epoch. INITFR is the fractional part of the Julian ephemeris date of initial epoch of the first record. INITFR has units of Julian days. INITFR has magnitude strictly less than 1 day. The sum INITJD + INITFR equals the Julian ephemeris date of the initial epoch of the first record. Detailed_OutputNone. This routine writes data to an SPK file. ParametersThe parameters described in this section are declared in the Fortran INCLUDE file spk20.inc MAXDEG is the maximum allowed degree of the input Chebyshev expansions. TOLSCL is a tolerance scale factor (also called a "relative tolerance") used for time coverage bound checking. TOLSCL is unitless. TOLSCL produces a tolerance value via the formula TOL = TOLSCL * MAX( ABS(FIRST), ABS(LAST) ) where FIRST and LAST are the coverage time bounds of a type 20 segment, expressed as seconds past J2000 TDB. The resulting parameter TOL is used as a tolerance for comparing the input segment descriptor time bounds to the first and last epoch covered by the sequence of time intervals defined by the inputs INITJD INITFR INTLEN N See the $Exceptions section below for a description of the error check using this tolerance. Exceptions1) If the number of sets of coefficients is not positive, the error SPICE(INVALIDCOUNT) is signaled. 2) If the interval length is not positive, the error SPICE(INTLENNOTPOS) is signaled. 3) If the name of the reference frame is not recognized, the error SPICE(INVALIDREFFRAME) is signaled. 4) If segment stop time is not greater than or equal to the begin time, the error SPICE(BADDESCRTIMES) is signaled. 5) If the start time of the first record exceeds the descriptor begin time by more than a computed tolerance, or if the end time of the last record precedes the descriptor end time by more than a computed tolerance, the error SPICE(COVERAGEGAP) is signaled. See the $Parameters section above for a description of the tolerance. 6) If the input degree POLYDG is less than 0 or greater than MAXDEG, the error SPICE(INVALIDDEGREE) is signaled. 7) If the last non-blank character of SEGID occurs past index 40, or if SEGID contains any nonprintable characters, an error is signaled by a routine in the call tree of this routine. 8) If either the distance or time scale is non-positive, the error SPICE(NONPOSITIVESCALE) is signaled. FilesA new type 20 SPK segment is written to the SPK file attached to HANDLE. ParticularsThis routine writes an SPK type 20 data segment to the designated SPK file, according to the format described in the SPK Required Reading. Each segment can contain data for only one target, central body, and reference frame. The Chebyshev polynomial degree and length of time covered by each logical record are also fixed. However, an arbitrary number of logical records of Chebyshev polynomial coefficients can be written in each segment. Minimizing the number of segments in an SPK file will help optimize how the SPICE system accesses the file. ExamplesSuppose that you have in an array CDATA sets of Chebyshev polynomial coefficients and position vectors representing the state of the moon (NAIF ID = 301), relative to the Earth-moon barycenter (NAIF ID = 3), in the J2000 reference frame, and you want to put these into a type 20 segment in an existing SPK file. The following code could be used to add one new type 20 segment. To add multiple segments, put the call to SPKW20 in a loop. C C First open the SPK file and get a handle for it. C CALL DAFOPW ( SPKNAM, HANDLE ) C C Create a segment identifier. C SEGID = 'MY_SAMPLE_SPK_TYPE_20_SEGMENT' C C Note that the interval length INTLEN has units C of Julian days. The start time of the first record C is expressed using two inputs: integer and fractional C portions of the Julian ephemeris date of the start C time. C C Write the segment. C CALL SPKW20 ( HANDLE, 301, 3, 'J2000', . FIRST, LAST, SEGID, INTLEN, . N, POLYDG, CDATA, DSCALE, . TSCALE, INITJD, INITFR ) C C Close the file. C CALL DAFCLS ( HANDLE ) RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) K.S. Zukor (JPL) VersionSPICELIB Version 1.0.1, 05-AUG-2021 (JDR) Edited the header to comply with NAIF standard. Added missing description of INITFR to $Brief_I/O section. SPICELIB Version 1.0.0, 17-JAN-2017 (NJB) (KSZ) |
Fri Dec 31 18:36:56 2021