Index of Functions: A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X
latcyl_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

```   latcyl_c ( Latitudinal to cylindrical coordinates )

SpiceDouble    lon,
SpiceDouble    lat,
SpiceDouble *  r,
SpiceDouble *  clon,
SpiceDouble *  z )

```

#### Abstract

```   Convert from latitudinal coordinates to cylindrical coordinates.
```

```   None.
```

#### Keywords

```   CONVERSION
COORDINATES

```

#### Brief_I/O

```   VARIABLE  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.
r          O   Distance of the point from the z axis.
clon       O   Angle of the point from the XZ plane in radians.
z          O   Height of the point above the XY plane.
```

#### Detailed_Input

```   radius      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

```   r           is the distance of the point from the z axis.

clon        is the angle of the point from the XZ plane in radians.
`clon' is set equal to `lon'.

z           is the height of the point above the XY plane.
```

#### Parameters

```   None.
```

#### Exceptions

```   Error free.
```

#### Files

```   None.
```

#### Particulars

```   This routine returns the cylindrical 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 cylindrical and
rectangular coordinates.

Use the meta-kernel shown below to load the required SPICE
kernels.

KPL/MK

File name: latcyl_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 latcyl_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

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

/.
Load SPK and LSK kernels, use a meta kernel for
convenience.
./
furnsh_c ( "latcyl_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 coordinates to cylindrical.
./
latcyl_c ( radius, lon, lat, &r, &clon, &z );

/.
Convert the cylindrical coordinates to rectangular.
./
cylrec_c ( r, clon, z, 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( "Cylindrical coordinates:\n" );
printf( " \n" );
printf( " Radius     (km):  %19.8f\n", r );
printf( " Longitude (deg):  %19.8f\n", clon*dpr_c ( ) );
printf( " Z          (km):  %19.8f\n", z );
printf( " \n" );
printf( "Rectangular coordinates from cylrec_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

Cylindrical coordinates:

Longitude (deg):         -98.34959789
Z          (km):     -126505.93063865

Rectangular coordinates from cylrec_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 cylindrical coordinates.

Corresponding latitudinal and cylindrical coordinates are
listed to three decimal places. Input and output angles are
in degrees.

Example code begins here.

/.
Program latcyl_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local parameters.
./
#define NREC         11

/.
Local variables.
./
SpiceDouble          clon;
SpiceDouble          r;
SpiceDouble          rlat;
SpiceDouble          rlon;
SpiceDouble          z;

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       clon      z   \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 ( );

latcyl_c ( radius[i], rlon, rlat, &r, &clon, &z );

printf( "%8.3f %8.3f %8.3f ", radius[i], lon[i], lat[i] );
printf( "%8.3f %8.3f %8.3f\n", r, clon * dpr_c ( ), z );

}

return ( 0 );
}

When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:

radius    lon      lat       r       clon      z
-------  -------  -------  -------  -------  -------
0.000    0.000   90.000    0.000    0.000    0.000
1.000    0.000    0.000    1.000    0.000    0.000
1.000   90.000    0.000    1.000   90.000    0.000
1.000    0.000   90.000    0.000    0.000    1.000
1.414  180.000   45.000    1.000  180.000    1.000
1.000  -90.000    0.000    1.000  -90.000    0.000
1.000    0.000  -90.000    0.000    0.000   -1.000
1.000   45.000    0.000    1.000   45.000    0.000
1.414  180.000  -45.000    1.000  180.000   -1.000
1.000  180.000   90.000    0.000  180.000    1.000
0.000   33.000    0.000    0.000   33.000    0.000

3) Other than the obvious conversion between coordinate systems
this routine could be used to obtain the axial projection
from a sphere to a cylinder about the z-axis that contains
the equator of the sphere.

Such a projection is valuable because it preserves the
areas between regions on the sphere and their projections to
the cylinder.

Example code begins here.

/.
Program latcyl_ex3
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local variables
./
SpiceDouble          clon;
SpiceDouble          lat;
SpiceDouble          lon;
SpiceDouble          r;
SpiceDouble          z;

/.
Define the point whose projection is to be
computed.
./
lon    =   45.0  * rpd_c ( );
lat    =  -12.5 * rpd_c ( );

/.
Convert the latitudinal coordinates to cylindrical.
./
latcyl_c ( radius, lon, lat, &r, &clon, &z );

printf( "Coordinates of the projected point on cylinder:\n" );
printf( " \n" );
printf( " Radius     (km):  %22.11f\n", r );
printf( " Longitude (deg):  %22.11f\n", clon*dpr_c ( ) );
printf( " Z          (km):  %22.11f\n", z );

return ( 0 );
}

When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:

Coordinates of the projected point on cylinder:

Longitude (deg):          45.00000000000
Z          (km):         -21.64396139381
```

#### Restrictions

```   None.
```

#### Literature_References

```   None.
```

#### Author_and_Institution

```   J. Diaz del Rio     (ODC Space)
B.V. Semenov        (JPL)
W.L. Taber          (JPL)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.1.0, 04-JUL-2021 (JDR)

Edited the header to comply with NAIF standard.

Changed the input argument name "lonc" to "clon" for consistency
with other routines.

-CSPICE Version 1.0.1, 26-JUL-2016 (BVS)

```   latitudinal to cylindrical coordinates
`Fri Dec 31 18:41:08 2021`