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reclat_c

 Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input Detailed_Output Parameters Exceptions Files Particulars Examples Restrictions Literature_References Author_and_Institution Version Index_Entries

Procedure

```   reclat_c ( Rectangular to latitudinal coordinates )

void reclat_c ( ConstSpiceDouble    rectan[3],
SpiceDouble       * lon,
SpiceDouble       * lat      )

```

Abstract

```   Convert from rectangular coordinates to latitudinal coordinates.
```

```   None.
```

Keywords

```   CONVERSION
COORDINATES

```

Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
rectan     I   Rectangular coordinates of a point.
radius     O   Distance of the point from the origin.
lon        O   Longitude of the point in radians.
lat        O   Latitude of the point in radians.
```

Detailed_Input

```   rectan      are the rectangular coordinates of the input point.
`rectan' is a 3-vector.
```

Detailed_Output

```   radius      is the distance of the point from the origin.

The units associated with `radius' are those
associated with the input `rectan'.

lon         is the longitude of the input point. This is 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 output in radians. The range of `lon'
is [-pi, pi].

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 output in radians. The range of `lat'
is [-pi/2, pi/2].
```

Parameters

```   None.
```

Exceptions

```   Error free.

1)  If the X and Y components of `rectan' are both zero, the
longitude is set to zero.

2)  If `rectan' is the zero vector, longitude and latitude are
both set to zero.
```

Files

```   None.
```

Particulars

```   This routine returns the latitudinal coordinates of a point
whose position is input in rectangular 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 thes 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: reclat_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

'naif0012.tls'  )

\begintext

End of meta-kernel

Example code begins here.

/.
Program reclat_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local variables
./
SpiceDouble          et;
SpiceDouble          lat;
SpiceDouble          lon;
SpiceDouble          lt;
SpiceDouble          pos    [3];
SpiceDouble          rectan [3];

/.
Load SPK and LSK kernels, use a meta kernel for
convenience.
./
furnsh_c ( "reclat_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, &lt );

/.
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( " 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:

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 rectangular coordinates
and the corresponding latitudinal coordinates.

Corresponding rectangular and latitudinal coordinates are
listed to three decimal places. Output angles are in degrees.

Example code begins here.

/.
Program reclat_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local parameters.
./
#define NREC         11

/.
Local variables.
./
SpiceDouble          lat;
SpiceDouble          lon;

SpiceInt             i;

/.
Define the input rectangular coordinates.
./
SpiceDouble          rectan [NREC][3] = {
{ 0.0,         0.0,         0.0},
{ 1.0,         0.0,         0.0},
{ 0.0,         1.0,         0.0},
{ 0.0,         0.0,         1.0},
{-1.0,         0.0,         0.0},
{ 0.0,        -1.0,         0.0},
{ 0.0,         0.0,        -1.0},
{ 1.0,         1.0,         0.0},
{ 1.0,         0.0,         1.0},
{ 0.0,         1.0,         1.0},
{ 1.0,         1.0,         1.0} };

/.
Print the banner.
./
printf( " rect[0]  rect[1]  rect[2]   radius    lon      lat\n"   );
printf( " -------  -------  -------  -------  -------  -------\n" );

/.
Do the conversion. Output angles are in degrees.
./
for ( i = 0; i < NREC; i++ )
{

reclat_c ( rectan[i], &radius, &lon, &lat );

printf( "%8.3f %8.3f %8.3f ", rectan[i][0], rectan[i][1],
rectan[i][2]               );
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:

rect[0]  rect[1]  rect[2]   radius    lon      lat
-------  -------  -------  -------  -------  -------
0.000    0.000    0.000    0.000    0.000    0.000
1.000    0.000    0.000    1.000    0.000    0.000
0.000    1.000    0.000    1.000   90.000    0.000
0.000    0.000    1.000    1.000    0.000   90.000
-1.000    0.000    0.000    1.000  180.000    0.000
0.000   -1.000    0.000    1.000  -90.000    0.000
0.000    0.000   -1.000    1.000    0.000  -90.000
1.000    1.000    0.000    1.414   45.000    0.000
1.000    0.000    1.000    1.414    0.000   45.000
0.000    1.000    1.000    1.414   90.000   45.000
1.000    1.000    1.000    1.732   45.000   35.264
```

Restrictions

```   None.
```

Literature_References

```   None.
```

Author_and_Institution

```   N.J. Bachman        (JPL)
J. Diaz del Rio     (ODC Space)
E.D. Wright         (JPL)
```

Version

```   -CSPICE Version 1.3.0, 10-AUG-2021 (JDR)

Changed input argument names "longitude" and "latitude to "lon"
and "lat" for consistency with other routines.

complete code example based on existing example.

-CSPICE Version 1.2.1, 30-JUL-2003 (NJB)

-CSPICE Version 1.2.0, 28-AUG-2001 (NJB)

Removed tab characters from source file. Now includes

-CSPICE Version 1.1.0, 21-OCT-1998 (NJB)

-CSPICE Version 1.0.0, 08-FEB-1998 (EDW)
```

Index_Entries

```   rectangular to latitudinal coordinates
```
`Fri Dec 31 18:41:11 2021`