| sphlat_c |
|
Table of contents
Procedure
sphlat_c ( Spherical to latitudinal coordinates )
void sphlat_c ( SpiceDouble r,
SpiceDouble colat,
SpiceDouble slon,
SpiceDouble * radius,
SpiceDouble * lon,
SpiceDouble * lat )
AbstractConvert from spherical coordinates to latitudinal coordinates. Required_ReadingNone. KeywordsCONVERSION COORDINATES Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- r I Distance of the point from the origin. colat I Angle of the point from positive z axis (radians). slon I Angle of the point from the XZ plane (radians). radius O Distance of a point from the origin lon O Angle of the point from the XZ plane in radians lat O Angle of the point from the XY plane in radians Detailed_Input
r 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.
slon is the angle of the point from the XZ plane (radians).
Detailed_Output
radius is the distance of a point from the origin.
lon is the angle of the point from the XZ plane in
radians. `lon' is set equal to `slon'.
lat is the angle of the point from the XY plane in
radians. `lat' is computed as pi/2 - colat.
ParametersNone. ExceptionsError free. FilesNone. ParticularsThis routine returns the latitudinal coordinates of a point whose position is input in spherical 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) Latitude is obtained by subtracting co-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 spherical coordinates of the position of the Moon as seen from the Earth, and convert them to latitudinal and rectangular coordinates. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: sphlat_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 sphlat_ex2 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local variables ./ SpiceDouble colat; SpiceDouble et; SpiceDouble lt; SpiceDouble lat; SpiceDouble lon; 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 ( "sphlat_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 spherical coordinates. ./ recsph_c ( pos, &r, &colat, &slon ); /. Convert the spherical coordinates to latitudinal. ./ sphlat_c ( r, colat, slon, &radius, &lon, &lat ); /. Convert the latitudinal coordinates to rectangular. ./ latrec_c ( radius, lon, lat, 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", r ); printf( " Colatitude (deg): %19.8f\n", colat*dpr_c ( ) ); printf( " Longitude (deg): %19.8f\n", slon*dpr_c ( ) ); 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( "Rectangular coordinates from latrec_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 Latitudinal coordinates: Radius (km): 403626.33912495 Longitude (deg): -98.34959789 Latitude (deg): -18.26566077 Rectangular coordinates from latrec_c: X (km): -55658.44323296 Y (km): -379226.32931475 Z (km): -126505.93063865 3) Create a table showing a variety of spherical coordinates and the corresponding cylindrical coordinates. Corresponding spherical and cylindrical coordinates are listed to three decimal places. Input and output angles are in degrees. Example code begins here. /. Program sphlat_ex3 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define NREC 11 /. Local variables. ./ SpiceDouble lat; SpiceDouble lon; SpiceDouble radius; SpiceDouble rcolat; SpiceDouble rslon; SpiceInt i; /. Define the input spherical coordinates. Angles in degrees. ./ SpiceDouble r [NREC] = { 0.0, 1.0, 1.0, 1.0, 1.4142, 1.0, 1.0, 1.0, 1.4142, 1.0, 0.0 }; SpiceDouble colat [NREC] = { 0.0, 90.0, 90.0, 0.0, 45.0, 90.0, 180.0, 90.0, 135.0, 0.0, 90.0 }; SpiceDouble slon [NREC] = { 0.0, 0.0, 90.0, 0.0, 180.0, -90.0, 0.0, 45.0, 180.0, 180.0, 33.0 }; /. Print the banner. ./ printf( " r colat slon radius lon lat\n" ); printf( " ------- ------- ------- ------- ------- -------\n" ); /. Do the conversion. Output angles in degrees. ./ for ( i = 0; i < NREC; i++ ) { rcolat = colat[i] * rpd_c ( ); rslon = slon[i] * rpd_c ( ); sphlat_c ( r[i], rcolat, rslon, &radius, &lon, &lat ); printf( "%8.3f %8.3f %8.3f ", r[i], colat[i], slon[i] ); printf( "%8.3f %8.3f %8.3f\n", radius, lon * dpr_c ( ), lat * dpr_c ( ) ); } return ( 0 ); } When this program was executed on a Mac/Intel/cc/64-bit platform, the output was: r colat slon radius lon lat ------- ------- ------- ------- ------- ------- 0.000 0.000 0.000 0.000 0.000 90.000 1.000 90.000 0.000 1.000 0.000 0.000 1.000 90.000 90.000 1.000 90.000 0.000 1.000 0.000 0.000 1.000 0.000 90.000 1.414 45.000 180.000 1.414 180.000 45.000 1.000 90.000 -90.000 1.000 -90.000 0.000 1.000 180.000 0.000 1.000 0.000 -90.000 1.000 90.000 45.000 1.000 45.000 0.000 1.414 135.000 180.000 1.414 180.000 -45.000 1.000 0.000 180.000 1.000 180.000 90.000 0.000 90.000 33.000 0.000 33.000 0.000 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 "lons" 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 latitudinal coordinates |
Fri Dec 31 18:41:12 2021