latrec |
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ProcedureLATREC ( Latitudinal to rectangular coordinates ) SUBROUTINE LATREC ( RADIUS, LON, LAT, RECTAN ) AbstractConvert from latitudinal coordinates to rectangular coordinates. Required_ReadingNone. KeywordsCONVERSION COORDINATES DeclarationsIMPLICIT NONE DOUBLE PRECISION RADIUS DOUBLE PRECISION LON DOUBLE PRECISION LAT DOUBLE PRECISION RECTAN ( 3 ) Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- RADIUS I Distance of a point from the origin. LON I Longitude of point in radians. LAT I Latitude of point in radians. RECTAN O Rectangular coordinates of the point. Detailed_InputRADIUS is the distance of a point from the origin. LON is the Longitude of the input point. This is the angle between the prime meridian and the meridian containing the point. The direction of increasing longitude is from the +X axis towards the +Y axis. Longitude is measured in radians. On input, the range of longitude is unrestricted. LAT is the latitude of the input point. This is the angle from the XY plane of the ray from the origin through the point. Latitude is measured in radians. On input, the range of latitude is unrestricted. Detailed_OutputRECTAN are the rectangular coordinates of the input point. RECTAN is a 3-vector. The units associated with RECTAN are those associated with the input RADIUS. ParametersNone. ExceptionsError free. FilesNone. ParticularsThis routine returns the rectangular coordinates of a point whose position is input in latitudinal coordinates. Latitudinal coordinates are defined by a distance from a central reference point, an angle from a reference meridian, and an angle above the equator of a sphere centered at the central reference point. ExamplesThe numerical results shown for these examples 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) Compute the latitudinal coordinates of the position of the Moon as seen from the Earth, and convert them to rectangular coordinates. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: latrec_ex1.tm This meta-kernel is intended to support operation of SPICE example programs. The kernels shown here should not be assumed to contain adequate or correct versions of data required by SPICE-based user applications. In order for an application to use this meta-kernel, the kernels referenced here must be present in the user's current working directory. The names and contents of the kernels referenced by this meta-kernel are as follows: File name Contents --------- -------- de421.bsp Planetary ephemeris naif0012.tls Leapseconds \begindata KERNELS_TO_LOAD = ( 'de421.bsp', 'naif0012.tls' ) \begintext End of meta-kernel Example code begins here. PROGRAM LATREC_EX1 IMPLICIT NONE C C SPICELIB functions C DOUBLE PRECISION DPR C C Local parameters C CHARACTER*(*) FMT1 PARAMETER ( FMT1 = '(A,F20.8)' ) C C Local variables C DOUBLE PRECISION ET DOUBLE PRECISION LAT DOUBLE PRECISION LON DOUBLE PRECISION LT DOUBLE PRECISION POS ( 3 ) DOUBLE PRECISION RADIUS DOUBLE PRECISION RECTAN ( 3 ) C C Load SPK and LSK kernels, use a meta kernel for C convenience. C CALL FURNSH ( 'latrec_ex1.tm' ) C C Look up the geometric state of the Moon as seen from C the Earth at 2017 Mar 20, relative to the J2000 C reference frame. C CALL STR2ET ( '2017 Mar 20', ET ) CALL SPKPOS ( 'Moon', ET, 'J2000', 'NONE', . 'Earth', POS, LT ) C C Convert the position vector POS to latitudinal C coordinates. C CALL RECLAT ( POS, RADIUS, LON, LAT ) C C Convert the latitudinal to rectangular coordinates. C CALL LATREC ( RADIUS, LON, LAT, RECTAN ) WRITE(*,*) ' ' WRITE(*,*) 'Original rectangular coordinates:' WRITE(*,*) ' ' WRITE(*,FMT1) ' X (km): ', POS(1) WRITE(*,FMT1) ' Y (km): ', POS(2) WRITE(*,FMT1) ' Z (km): ', POS(3) WRITE(*,*) ' ' WRITE(*,*) 'Latitudinal coordinates:' WRITE(*,*) ' ' WRITE(*,FMT1) ' Radius (km): ', RADIUS WRITE(*,FMT1) ' Longitude (deg): ', LON*DPR() WRITE(*,FMT1) ' Latitude (deg): ', LAT*DPR() WRITE(*,*) ' ' WRITE(*,*) 'Rectangular coordinates from LATREC:' WRITE(*,*) ' ' WRITE(*,FMT1) ' X (km): ', RECTAN(1) WRITE(*,FMT1) ' Y (km): ', RECTAN(2) WRITE(*,FMT1) ' Z (km): ', RECTAN(3) WRITE(*,*) ' ' END When this program was executed on a Mac/Intel/gfortran/64-bit platform, the output was: Original rectangular coordinates: X (km): -55658.44323296 Y (km): -379226.32931475 Z (km): -126505.93063865 Latitudinal coordinates: Radius (km): 403626.33912495 Longitude (deg): -98.34959789 Latitude (deg): -18.26566077 Rectangular coordinates from LATREC: X (km): -55658.44323296 Y (km): -379226.32931475 Z (km): -126505.93063865 2) Create a table showing a variety of latitudinal coordinates and the corresponding rectangular coordinates. Corresponding latitudinal and rectangular coordinates are listed to three decimal places. Input angles are in degrees. Example code begins here. PROGRAM LATREC_EX2 IMPLICIT NONE C C SPICELIB functions C DOUBLE PRECISION DPR DOUBLE PRECISION RPD C C Local parameters. C INTEGER NREC PARAMETER ( NREC = 11 ) C C Local variables. C DOUBLE PRECISION LAT ( NREC ) DOUBLE PRECISION LON ( NREC ) DOUBLE PRECISION RADIUS ( NREC ) DOUBLE PRECISION RECTAN ( 3 ) DOUBLE PRECISION RLAT DOUBLE PRECISION RLON INTEGER I C C Define the input latitudinal coordinates. Angles in C degrees. C DATA RADIUS / 0.D0, 1.D0, 1.D0, . 1.D0, 1.D0, 1.D0, . 1.D0, 1.4142D0, 1.4142D0, . 1.4142D0, 1.732D0 / DATA LON / 0.D0, 0.D0, 90.D0, . 0.D0, 180.D0, -90.D0, . 0.D0, 45.D0, 0.D0, . 90.D0, 45.D0 / DATA LAT / 0.D0, 0.D0, 0.D0, . 90.D0, 0.D0, 0.D0, . -90.D0, 0.D0, 45.D0, . 45.D0, 35.264D0 / C C Print the banner. C WRITE(*,*) ' RADIUS LON LAT ' . // ' RECT(1) RECT(2) RECT(3) ' WRITE(*,*) ' ------- ------- ------- ' . // ' ------- ------- ------- ' C C Do the conversion. C DO I = 1, NREC RLON = LON(I) * RPD() RLAT = LAT(I) * RPD() CALL LATREC( RADIUS(I), RLON, RLAT, RECTAN ) WRITE (*,'(6F9.3)') RADIUS(I), LON(I), LAT(I), . RECTAN END DO END When this program was executed on a Mac/Intel/gfortran/64-bit platform, the output was: RADIUS LON LAT RECT(1) RECT(2) RECT(3) ------- ------- ------- ------- ------- ------- 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 1.000 0.000 0.000 1.000 90.000 0.000 0.000 1.000 0.000 1.000 0.000 90.000 0.000 0.000 1.000 1.000 180.000 0.000 -1.000 0.000 0.000 1.000 -90.000 0.000 0.000 -1.000 0.000 1.000 0.000 -90.000 0.000 0.000 -1.000 1.414 45.000 0.000 1.000 1.000 0.000 1.414 0.000 45.000 1.000 0.000 1.000 1.414 90.000 45.000 0.000 1.000 1.000 1.732 45.000 35.264 1.000 1.000 1.000 RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionC.H. Acton (JPL) N.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) VersionSPICELIB Version 1.1.0, 06-JUL-2021 (JDR) Changed the input argument name LONG to LON for consistency with other routines. Added IMPLICIT NONE statement. Edited the header to comply with NAIF standard. Removed unnecessary $Revisions section. Added complete code examples. SPICELIB Version 1.0.2, 29-JUL-2003 (NJB) (CHA) Various header changes were made to improve clarity. Some minor header corrections were made. SPICELIB Version 1.0.1, 10-MAR-1992 (WLT) Comment section for permuted index source lines was added following the header. SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) |
Fri Dec 31 18:36:30 2021