Table of contents
CSPICE_LATCYL converts from latitudinal coordinates to
cylindrical coordinates.
Given:
radius the value(s) describing the distance of the position
from the origin.
[1,n] = size(radius); double = class(radius)
lon the value(s) describing the angle of the position from
the XZ plane measured in radians.
[1,n] = size(lon); double = class(lon)
lat the value(s) describing the angle of the position from the
XY plane measured in radians.
[1,n] = size(lat); double = class(lat)
the call:
[ r, clon, z] = cspice_latcyl( radius, lon, lat)
returns:
r the value(s) describing the distance of the point of
interest from z axis.
[1,n] = size(r); double = class(r)
clon the value(s) describing the cylindrical angle of the point of
interest from the XZ plane measured in radians.
[1,n] = size(clon); double = class(clon)
z the value(s) describing the height of the point above
the XY plane.
[1,n] = size(z); double = class(z)
The arguments 'r' and 'z' return in the same units associated
with 'radius'.
'r', 'clon', and 'z' return with the same vectorization
measure, N, as the 'radius', 'lon', and 'lat'.
None.
Any numerical results shown for these examples may differ between
platforms as the results depend on the SPICE kernels used as input
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
KERNELS_TO_LOAD = ( 'de421.bsp',
'naif0012.tls' )
\begintext
End of meta-kernel
Example code begins here.
function latcyl_ex1()
%
% Load an SPK and leapseconds kernels.
%
cspice_furnsh( 'latcyl_ex1.tm' )
%
% Convert the time to ET.
%
et = cspice_str2et( '2017 Mar 20' );
%
% Retrieve the position of the moon seen from earth at 'et'
% in the J2000 frame without aberration correction.
%
[pos, et] = cspice_spkpos( 'MOON', et, 'J2000', 'NONE', 'EARTH' );
fprintf( 'Original rectangular coordinates:\n' )
fprintf( ' X (km): %20.8f\n', pos(1) )
fprintf( ' Y (km): %20.8f\n', pos(2) )
fprintf( ' Z (km): %20.8f\n', pos(3) )
%
% Convert the position vector 'pos' to latitudinal
% coordinates.
%
[radius, lon, lat] = cspice_reclat(pos);
fprintf( '\n' )
fprintf( 'Latitudinal coordinates:\n' )
fprintf( ' Radius (km): %20.8f\n', radius )
fprintf( ' Longitude (deg): %20.8f\n', lon * cspice_dpr )
fprintf( ' Latitude (deg): %20.8f\n', lat * cspice_dpr )
%
% Convert the latitudinal coords to cylindrical.
%
[r, clon, z ] = cspice_latcyl( radius, lon, lat);
fprintf( '\n' )
fprintf( 'Cylindrical coordinates:\n' )
fprintf( ' Radius (km): %20.8f\n', r )
fprintf( ' Longitude (deg): %20.8f\n', clon * cspice_dpr )
fprintf( ' Z (km): %20.8f\n', z )
%
% Convert the cylindrical to rectangular.
%
[rectan] = cspice_cylrec( r, clon, z);
fprintf( '\n' )
fprintf( 'Rectangular coordinates from cspice_cylrec:\n' )
fprintf( ' X (km): %20.8f\n', rectan(1) )
fprintf( ' Y (km): %20.8f\n', rectan(2) )
fprintf( ' Z (km): %20.8f\n', rectan(3) )
%
% It's always good form to unload kernels after use,
% particularly in MATLAB due to data persistence.
%
cspice_kclear
When this program was executed on a Mac/Intel/Octave6.x/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
Cylindrical coordinates:
Radius (km): 383289.01777726
Longitude (deg): -98.34959789
Z (km): -126505.93063865
Rectangular coordinates from cspice_cylrec:
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.
function latcyl_ex2()
%
% Define six sets of latitudinal coordinates, `lon' and `lat'
% expressed in degrees - converted to radians by use
% of cspice_rpd.
%
rad = [ 1., 1., sqrt(2.), sqrt(2.), 1., 0. ];
lon = [ 0., 90., 180., 180., 180., 33. ] * cspice_rpd;
lat = [ 0., 0., 45., -45., 90., 0. ] * cspice_rpd;
%
% ...convert the latitudinal coordinates to cylindrical coordinates
%
[r, clon, z] = cspice_latcyl(rad, lon, lat);
%
% ...convert angular measure to degrees.
%
clon = clon * cspice_dpr;
lon = lon * cspice_dpr;
lat = lat * cspice_dpr;
%
% Output banner.
%
disp(' r clon z radius lon lat ')
disp(' ------- -------- -------- ------- -------- --------')
%
% Create an array of values for output.
%
output = [ r; clon; z; rad; lon; lat ];
txt = sprintf( '%9.3f %9.3f %9.3f %9.3f %9.3f %9.3f\n', output );
disp( txt )
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
r clon z radius lon lat
------- -------- -------- ------- -------- --------
1.000 0.000 0.000 1.000 0.000 0.000
1.000 90.000 0.000 1.000 90.000 0.000
1.000 180.000 1.000 1.414 180.000 45.000
1.000 180.000 -1.000 1.414 180.000 -45.000
0.000 180.000 1.000 1.000 180.000 90.000
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.
function latcyl_ex3()
%
% Define the point whose projection is to be
% computed.
%
radius = 100.0;
lon = 45.0 * cspice_rpd;
lat = -12.5 * cspice_rpd;
%
% Convert the latitudinal coordinates to cylindrical.
%
[r, clon, z] = cspice_latcyl( radius, lon, lat );
fprintf( 'Coordinates of the projected point on cylinder:\n' )
fprintf( ' \n' )
fprintf( ' Radius (km): %22.11f\n', r )
fprintf( ' Longitude (deg): %22.11f\n', clon*cspice_dpr )
fprintf( ' Z (km): %22.11f\n', z )
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
Coordinates of the projected point on cylinder:
Radius (km): 97.62960071199
Longitude (deg): 45.00000000000
Z (km): -21.64396139381
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.
1) If any of the input arguments, `radius', `lon' or `lat', is
undefined, an error is signaled by the Matlab error handling
system.
2) If any of the input arguments, `radius', `lon' or `lat', is
not of the expected type, or it does not have the expected
dimensions and size, an error is signaled by the Mice
interface.
3) If the input vectorizable arguments `radius', `lon' and `lat'
do not have the same measure of vectorization (N), an error is
signaled by the Mice interface.
None.
None.
MICE.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Mice Version 1.1.0, 10-AUG-2021 (EDW) (JDR)
Changed input argument name "lonc" to "clon" for consistency
with other routines.
Edited the -Examples section to comply with NAIF standard. Added
meta-kernel to example #1. Updated code example #1 to produce
formatted output and added a call to cspice_kclear. Added the
problem statement to both examples.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections, and
completed -Particulars section.
Eliminated use of "lasterror" in rethrow.
Removed reference to the function's corresponding CSPICE header from
-Required_Reading section.
-Mice Version 1.0.1, 01-DEC-2014 (EDW)
Edited -I/O section to conform to NAIF standard for Mice
documentation.
-Mice Version 1.0.0, 09-DEC-2005 (EDW)
latitudinal to cylindrical coordinates
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