| sphrec_c |
|
Table of contents
Procedure
sphrec_c ( Spherical to rectangular coordinates )
void sphrec_c ( SpiceDouble r,
SpiceDouble colat,
SpiceDouble slon,
SpiceDouble rectan[3] )
AbstractConvert from spherical coordinates to rectangular coordinates. Required_ReadingNone. KeywordsCONVERSION COORDINATES Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- r I Distance of a point from the origin. colat I Angle of the point from the Z-axis in radians. slon I Angle of the point from the XZ plane in radians. rectan O Rectangular coordinates of the point. Detailed_Input
r is the distance of the point from the origin.
colat is the angle between the point and the positive z-axis in
radians.
slon is the angle of the projection of the point to the XY plane
from the positive X-axis in radians. The positive Y-axis is
at longitude PI/2 radians.
Detailed_Outputrectan are the rectangular coordinates of a point. ParametersNone. ExceptionsError free. FilesNone. ParticularsThis routine returns the rectangular coordinates of a point whose position is input in spherical coordinates. Spherical coordinates are defined by a distance from a central reference point, an angle from a reference meridian, and an angle from the z-axis. The co-latitude of the positive Z-axis is zero. The longitude of the posive Y-axis is PI/2 radians. 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 spherical 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: sphrec_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 sphrec_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
SpiceDouble colat;
SpiceDouble et;
SpiceDouble lt;
SpiceDouble pos [3];
SpiceDouble radius;
SpiceDouble rectan [3];
SpiceDouble slon;
/.
Load SPK and LSK kernels, use a meta kernel for
convenience.
./
furnsh_c ( "sphrec_ex1.tm" );
/.
Look up the geometric state of the Moon as seen from
the Earth at 2017 Mar 20, relative to the J2000
reference frame.
./
str2et_c ( "2017 Mar 20", &et );
spkpos_c ( "Moon", et, "J2000", "NONE", "Earth", pos, < );
/.
Convert the position vector `pos' to spherical
coordinates.
./
recsph_c ( pos, &radius, &colat, &slon );
/.
Convert the spherical coordinates to rectangular.
./
sphrec_c ( radius, colat, slon, rectan );
printf( " \n" );
printf( "Original rectangular coordinates:\n" );
printf( " \n" );
printf( " X (km): %19.8f\n", pos[0] );
printf( " Y (km): %19.8f\n", pos[1] );
printf( " Z (km): %19.8f\n", pos[2] );
printf( " \n" );
printf( "Spherical coordinates:\n" );
printf( " \n" );
printf( " Radius (km): %19.8f\n", radius );
printf( " Colatitude (deg): %19.8f\n", colat*dpr_c ( ) );
printf( " Longitude (deg): %19.8f\n", slon*dpr_c ( ) );
printf( " \n" );
printf( "Rectangular coordinates from sphrec_c:\n" );
printf( " \n" );
printf( " X (km): %19.8f\n", rectan[0] );
printf( " Y (km): %19.8f\n", rectan[1] );
printf( " Z (km): %19.8f\n", rectan[2] );
printf( " \n" );
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Original rectangular coordinates:
X (km): -55658.44323296
Y (km): -379226.32931475
Z (km): -126505.93063865
Spherical coordinates:
Radius (km): 403626.33912495
Colatitude (deg): 108.26566077
Longitude (deg): -98.34959789
Rectangular coordinates from sphrec_c:
X (km): -55658.44323296
Y (km): -379226.32931475
Z (km): -126505.93063865
2) Create a table showing a variety of spherical coordinates
and the corresponding rectangular coordinates.
Corresponding spherical and rectangular coordinates are
listed to three decimal places. Input angles are in degrees.
Example code begins here.
/.
Program sphrec_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local parameters.
./
#define NREC 11
/.
Local variables.
./
SpiceDouble rcolat;
SpiceDouble rslon;
SpiceDouble rectan [3];
SpiceInt i;
/.
Define the input spherical coordinates. Angles in degrees.
./
SpiceDouble radius [NREC] = { 0.0, 1.0, 1.0,
1.0, 1.0, 1.0,
1.0, 1.4142, 1.4142,
1.4142, 1.7320 };
SpiceDouble colat [NREC] = { 0.0, 90.0, 90.0,
0.0, 90.0, 90.0,
180.0, 90.0, 45.0,
45.0, 54.7356 };
SpiceDouble slon [NREC] = { 0.0, 0.0, 90.0,
0.0, 180.0, -90.0,
0.0, 45.0, 0.0,
90.0, 45.0 };
/.
Print the banner.
./
printf( " radius colat slon rect[0] rect[1] rect[2]\n" );
printf( " ------- ------- ------- ------- ------- -------\n" );
/.
Do the conversion.
./
for ( i = 0; i < NREC; i++ )
{
rcolat = colat[i] * rpd_c ( );
rslon = slon[i] * rpd_c ( );
sphrec_c ( radius[i], rcolat, rslon, rectan );
printf( "%8.3f %8.3f %8.3f ", radius[i], colat[i], slon[i] );
printf( "%8.3f %8.3f %8.3f\n", rectan[0], rectan[1], rectan[2] );
}
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
radius colat slon rect[0] rect[1] rect[2]
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 0.000
1.000 90.000 0.000 1.000 0.000 0.000
1.000 90.000 90.000 0.000 1.000 0.000
1.000 0.000 0.000 0.000 0.000 1.000
1.000 90.000 180.000 -1.000 0.000 0.000
1.000 90.000 -90.000 0.000 -1.000 0.000
1.000 180.000 0.000 0.000 0.000 -1.000
1.414 90.000 45.000 1.000 1.000 0.000
1.414 45.000 0.000 1.000 0.000 1.000
1.414 45.000 90.000 0.000 1.000 1.000
1.732 54.736 45.000 1.000 1.000 1.000
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionJ. Diaz del Rio (ODC Space) B.V. Semenov (JPL) W.L. Taber (JPL) E.D. Wright (JPL) Version
-CSPICE Version 1.1.0, 05-JUL-2021 (JDR)
Changed the output argument name "lon" to "slon" for
consistency with other routines.
Edited the header to comply with NAIF standard.
Added complete code examples.
-CSPICE Version 1.0.1, 26-JUL-2016 (BVS)
Minor headers edits.
-CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT)
Index_Entriesspherical to rectangular coordinates |
Fri Dec 31 18:41:12 2021