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sphcyl_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

```   sphcyl_c ( Spherical to cylindrical coordinates )

SpiceDouble     colat,
SpiceDouble     slon,
SpiceDouble   * r,
SpiceDouble   * clon,
SpiceDouble   * z )

```

#### Abstract

```   Convert from spherical coordinates to cylindrical coordinates.
```

```   None.
```

#### Keywords

```   CONVERSION
COORDINATES

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  -------------------------------------------------
radius     I   Distance of point from origin.
colat      I   Polar angle (co-latitude in radians) of point.
slon       I   Azimuthal angle (longitude) of point (radians).
r          O   Distance of point from Z axis.
clon       O   Angle (radians) of point from XZ plane.
z          O   Height of point above XY plane.
```

#### Detailed_Input

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

colat       is the polar angle (co-latitude in radians) of the point.

slon        is the azimuthal angle (longitude) of the point (radians).
```

#### Detailed_Output

```   r           is the distance of the point of interest from Z axis.

clon        is the cylindrical angle (radians) of the point from the
XZ plane. `clon' is set equal to `slon'.

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

#### Parameters

```   None.
```

#### Exceptions

```   Error free.
```

#### Files

```   None.
```

#### Particulars

```   This returns the cylindrical coordinates of a point whose
position is input through spherical coordinates.
```

#### 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 spherical 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: sphcyl_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 sphcyl_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

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

/.
Load SPK and LSK kernels, use a meta kernel for
convenience.
./
furnsh_c ( "sphcyl_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 spherical
coordinates.
./
recsph_c ( pos, &radius, &colat, &slon );

/.
Convert the spherical coordinates to cylindrical.
./
sphcyl_c ( radius, colat, slon, &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( "Spherical coordinates:\n" );
printf( " \n" );
printf( " Colatitude (deg):  %19.8f\n", colat*dpr_c ( ) );
printf( " Longitude  (deg):  %19.8f\n", slon*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

Spherical coordinates:

Colatitude (deg):         108.26566077
Longitude  (deg):         -98.34959789

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 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 sphcyl_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local parameters.
./
#define NREC         11

/.
Local variables.
./
SpiceDouble          clon;
SpiceDouble          r;
SpiceDouble          rcolat;
SpiceDouble          rslon;
SpiceDouble          z;

SpiceInt             i;

/.
Define the input spherical 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          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( "  radius   colat     slon      r       clon      z\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 ( );

sphcyl_c ( radius[i], rcolat, rslon, &r, &clon, &z );

printf( "%8.3f %8.3f %8.3f ", radius[i], colat[i], slon[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   colat     slon      r       clon      z
-------  -------  -------  -------  -------  -------
0.000    0.000    0.000    0.000    0.000    0.000
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    0.000    0.000    1.000
1.414   45.000  180.000    1.000  180.000    1.000
1.000   90.000  -90.000    1.000  -90.000    0.000
1.000  180.000    0.000    0.000    0.000   -1.000
1.000   90.000   45.000    1.000   45.000    0.000
1.414  135.000  180.000    1.000  180.000   -1.000
1.000    0.000  180.000    0.000  180.000    1.000
0.000   90.000   33.000    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 sphcyl_ex3
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local variables
./
SpiceDouble          clon;
SpiceDouble          colat;
SpiceDouble          r;
SpiceDouble          slon;
SpiceDouble          z;

/.
Define the point whose projection is to be
computed.
./
slon   =    45.0 * rpd_c();
colat  =   102.5 * rpd_c();

/.
Convert the spherical coordinates to cylindrical.
./
sphcyl_c ( radius, colat, slon, &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)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.1.0, 05-JUL-2021 (JDR)

Changed the output argument name "lon" to "clon" for
consistency with other routines.

Edited the header to comply with NAIF standard.
```   spherical to cylindrical coordinates
`Fri Dec 31 18:41:12 2021`