| latsph_c |
|
Table of contents
Procedure
latsph_c ( Latitudinal to spherical coordinates )
void latsph_c ( SpiceDouble radius,
SpiceDouble lon,
SpiceDouble lat,
SpiceDouble * rho,
SpiceDouble * colat,
SpiceDouble * slon )
AbstractConvert from latitudinal coordinates to spherical coordinates. Required_ReadingNone. KeywordsCONVERSION COORDINATES Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- radius I Distance of a point from the origin. lon I Angle of the point from the XZ plane in radians. lat I Angle of the point from the XY plane in radians. rho O Distance of the point from the origin. colat O Angle of the point from positive z axis (radians). slon O Angle of the point from the XZ plane (radians). Detailed_Inputradius is the distance of a point from the origin. lon is the angle of the point from the XZ plane in radians. lat is the angle of the point from the XY plane in radians. Detailed_Output
rho is the distance of the point from the origin.
colat is the angle between the vector from the origin to the point
and the positive z axis in radians. `colat' is computed
as pi/2 - `lat'.
slon is the angle of the point from the XZ plane (radians). `slon'
is set equal to `lon'.
ParametersNone. ExceptionsError free. FilesNone. ParticularsThis routine returns the spherical 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. 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. 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) Co-latitude is obtained by subtracting latitude from halfpi_c Radius and longitude mean the same thing in both latitudinal and spherical coordinates. The table below lists `lat' and corresponding `colat' in terms of degrees. LAT COLAT ----- ----- 0 90 20 70 45 45 -30 120 90 0 -45 135 2) Compute the latitudinal coordinates of the position of the Moon as seen from the Earth, and convert them to spherical and rectangular coordinates. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: latsph_ex2.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 latsph_ex2 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local variables ./ SpiceDouble colat; SpiceDouble et; SpiceDouble lat; SpiceDouble lon; SpiceDouble lt; SpiceDouble pos [3]; SpiceDouble r; SpiceDouble radius; SpiceDouble rectan [3]; SpiceDouble slon; /. Load SPK and LSK kernels, use a meta kernel for convenience. ./ furnsh_c ( "latsph_ex2.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 latitudinal coordinates. ./ reclat_c ( pos, &radius, &lon, &lat ); /. Convert the latitudinal coordinates to spherical. ./ latsph_c ( radius, lon, lat, &r, &colat, &slon ); /. Convert the spherical coordinates to rectangular. ./ sphrec_c ( r, 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( "Latitudinal coordinates:\n" ); printf( " \n" ); printf( " Radius (km): %19.8f\n", radius ); printf( " Longitude (deg): %19.8f\n", lon*dpr_c ( ) ); printf( " Latitude (deg): %19.8f\n", lat*dpr_c ( ) ); printf( " \n" ); printf( "Spherical coordinates:\n" ); printf( " \n" ); printf( " Radius (km): %19.8f\n", r ); 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 Latitudinal coordinates: Radius (km): 403626.33912495 Longitude (deg): -98.34959789 Latitude (deg): -18.26566077 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 3) Create a table showing a variety of latitudinal coordinates and the corresponding spherical coordinates. Corresponding latitudinal and spherical coordinates are listed to three decimal places. Input and output angles are in degrees. Example code begins here. /. Program latsph_ex3 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define NREC 11 /. Local variables. ./ SpiceDouble colat; SpiceDouble r; SpiceDouble rlat; SpiceDouble rlon; SpiceDouble slon; SpiceInt i; /. Define the input latitudinal coordinates. Angles in degrees. ./ SpiceDouble radius [NREC] = { 0.0, 1.0, 1.0, 1.0, 1.4142, 1.0, 1.0, 1.0, 1.4142, 1.0, 0.0 }; SpiceDouble lon [NREC] = { 0.0, 0.0, 90.0, 0.0, 180.0, -90.0, 0.0, 45.0, 180.0, 180.0, 33.0 }; SpiceDouble lat [NREC] = { 90.0, 0.0, 0.0, 90.0, 45.0, 0.0, -90.0, 0.0, -45.0, 90.0, 0.0 }; /. Print the banner. ./ printf( " radius lon lat r colat slon\n" ); printf( " ------- ------- ------- ------- ------- ------- \n" ); /. Do the conversion. Output angles in degrees. ./ for ( i = 0; i < NREC; i++ ) { rlon = lon[i] * rpd_c ( ); rlat = lat[i] * rpd_c ( ); latsph_c ( radius[i], rlon, rlat, &r, &colat, &slon ); printf( "%8.3f %8.3f %8.3f ", radius[i], lon[i], lat[i] ); printf( "%8.3f %8.3f %8.3f\n", r, colat * dpr_c ( ), slon * dpr_c ( ) ); } return ( 0 ); } When this program was executed on a Mac/Intel/cc/64-bit platform, the output was: radius lon lat r colat slon ------- ------- ------- ------- ------- ------- 0.000 0.000 90.000 0.000 0.000 0.000 1.000 0.000 0.000 1.000 90.000 0.000 1.000 90.000 0.000 1.000 90.000 90.000 1.000 0.000 90.000 1.000 0.000 0.000 1.414 180.000 45.000 1.414 45.000 180.000 1.000 -90.000 0.000 1.000 90.000 -90.000 1.000 0.000 -90.000 1.000 180.000 0.000 1.000 45.000 0.000 1.000 90.000 45.000 1.414 180.000 -45.000 1.414 135.000 180.000 1.000 180.000 90.000 1.000 0.000 180.000 0.000 33.000 0.000 0.000 90.000 33.000 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, 13-AUG-2021 (JDR)
Changed the output argument name "lons" to "slon" for
consistency with other routines.
Edited the header to comply with NAIF standard.
Added complete code examples.
-CSPICE Version 1.0.2, 26-JUL-2016 (BVS)
Minor headers edits.
-CSPICE Version 1.0.1, 13-DEC-2005 (EDW)
Corrected typo in -Detailed_Output, substituted
"colat" for "lat."
-CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT)
Index_Entrieslatitudinal to spherical coordinates |
Fri Dec 31 18:41:08 2021