| latrec_c |
|
Table of contents
Procedure
latrec_c ( Latitudinal to rectangular coordinates )
void latrec_c ( SpiceDouble radius,
SpiceDouble lon,
SpiceDouble lat,
SpiceDouble rectan[3] )
AbstractConvert from latitudinal coordinates to rectangular coordinates. Required_ReadingNone. KeywordsCONVERSION COORDINATES 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_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
`rectan'. The direction of increasing longitude is from
the +X axis towards the +Y axis.
`lon' 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.
`lat' 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'.
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. 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
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local variables
./
SpiceDouble et;
SpiceDouble lat;
SpiceDouble lon;
SpiceDouble lt;
SpiceDouble pos [3];
SpiceDouble radius;
SpiceDouble rectan [3];
/.
Load SPK and LSK kernels, use a meta kernel for
convenience.
./
furnsh_c ( "latrec_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 latitudinal
coordinates.
./
reclat_c ( pos, &radius, &lon, &lat );
/.
Convert the latitudinal to rectangular coordinates.
./
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( "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
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
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
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local constants.
./
#define NPTS 11
/.
Local variables.
./
SpiceDouble rectan[3];
SpiceDouble rlon;
SpiceDouble rlat;
SpiceInt i;
/.
Define eleven sets of latitude coordinates, `lon'
and `lat' expressed in degrees.
./
SpiceDouble radius[NPTS] = { 0.0, 1.0, 1.0,
1.0, 1.0, 1.0,
1.0, 1.4142, 1.4142,
1.4142, 1.732 };
SpiceDouble lon [NPTS] = { 0.0, 0.0, 90.0,
0.0, 180.0, -90.0,
0.0, 45.0, 0.0,
90.0, 45.0 };
SpiceDouble lat [NPTS] = { 0.0, 0.0, 0.0,
90.0, 0.0, 0.0,
-90.0, 0.0, 45.0,
45.0, 35.2643 };
/.
Print a header for the data output.
./
printf( " radius lon lat rect[0] rect[1] rect[2]\n" );
printf( " ------- ------- ------- ------- ------- -------\n" );
for ( i = 0; i < NPTS; i++ )
{
/.
Convert `lon' and `lat' from degrees to radians.
./
rlon = lon[i] * rpd_c();
rlat = lat[i] * rpd_c();
/.
Convert the coordinates from latitudinal to rectangular.
./
latrec_c ( radius[i], rlon, rlat, rectan );
/.
Output the row of the coordinate table.
./
printf ( "%8.3f %8.3f %8.3f %8.3f %8.3f %8.3f\n",
radius[i], lon[i], lat[i],
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 lon lat rect[0] rect[1] rect[2]
------- ------- ------- ------- ------- -------
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) E.D. Wright (JPL) Version
-CSPICE Version 1.1.0, 04-JUL-2021 (JDR)
Changed input argument names "longitude" and "latitude to "lon"
and "lat" for consistency with other routines.
Edited the header to comply with NAIF standard. Added
complete code examples based on existing example.
-CSPICE Version 1.0.1, 29-JUL-2003 (NJB) (CHA)
Various header corrections were made.
-CSPICE Version 1.0.0, 16-APR-1999 (EDW)
Index_Entrieslatitudinal to rectangular coordinates |
Fri Dec 31 18:41:08 2021