| latrec |
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Table of contents
Procedure
LATREC ( Latitudinal to rectangular coordinates )
SUBROUTINE LATREC ( RADIUS, LON, LAT, RECTAN )
Abstract
Convert from latitudinal coordinates to rectangular coordinates.
Required_Reading
None.
Keywords
CONVERSION
COORDINATES
Declarations
IMPLICIT NONE
DOUBLE PRECISION RADIUS
DOUBLE PRECISION LON
DOUBLE PRECISION LAT
DOUBLE PRECISION RECTAN ( 3 )
Brief_I/O
VARIABLE 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_Input
RADIUS 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_Output
RECTAN 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.
Parameters
None.
Exceptions
Error free.
Files
None.
Particulars
This 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.
Examples
The 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
Restrictions
None.
Literature_References
None.
Author_and_Institution
C.H. Acton (JPL)
N.J. Bachman (JPL)
J. Diaz del Rio (ODC Space)
W.L. Taber (JPL)
Version
SPICELIB 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)
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Fri Dec 31 18:36:30 2021