CSPICE_SUBSOL determines the coordinates of the sub-solar
point on a target body as seen by a specified observer at a
specified epoch, optionally corrected for planetary (light time)
and stellar aberration.
Deprecated: This routine has been superseded by the routine
cspice_subslr. This routine is supported for purposes of
backward compatibility only.
method the name for the computation method to use.
[1,c1] = size(method); char = class(method)
[1,1] = size(method); cell = class(method)
The choices are:
'Near point' The sub-solar point is defined
as the nearest point on the
target to the sun.
'Intercept' The sub-observer point is defined
as the target surface intercept of
the line containing the target's
center and the sun's center.
In both cases, the intercept computation treats the
surface of the target body as a triaxial ellipsoid.
The ellipsoid's radii must be available in the kernel
Neither case nor white space are significant in
method. For example, the string ' NEARPOINT' is
target the name of the target body. 'target' is case-insensitive,
and leading and trailing blanks in 'target' are not
significant. Optionally, you may supply a string containing
the integer ID code for the object. For example both 'MOON'
and '301' are legitimate strings that indicate the moon is
the target body.
[1,c2] = size(target); char = class(target)
[1,1] = size(target); cell = class(target)
This routine assumes that the target body is modeled by
a tri-axial ellipsoid, and that a PCK file containing
its radii has been loaded into the kernel pool via
et the value(s) for ephemeris time expressed as ephemeris seconds
past J2000 at which the sub-solar point on the target body
is to be computed.
[1,n] = size(et); double = class(et)
abcorr the aberration corrections to apply when computing the
[1,c3] = size(abcorr); char = class(abcorr)
[1,1] = size(abcorr); cell = class(abcorr)
'abcorr' may be any of the following.
'NONE' Apply no correction. Return the
geometric sub-solar point on the target
'LT' Correct for planetary (light time)
aberration. Both the state and rotation
of the target body are corrected for one
way light time from target to observer.
The state of the sun relative to the
target is corrected for one way light
from the sun to the target; this state
is evaluated at the epoch obtained by
retarding et by the one way light time
from target to observer.
'LT+S' Correct for planetary (light time) and
stellar aberrations. Light time
corrections are the same as in the 'LT'
case above. The target state is
additionally corrected for stellar
aberration as seen by the observer, and
the sun state is corrected for stellar
aberration as seen from the target.
'CN' Converged Newtonian light time correction.
This option produces a solution that is at
least as accurate at that obtainable
with the 'LT' option. Whether the 'CN'
solution is substantially more accurate
depends on the geometry of the
participating objects and on the
accuracy of the input data. In all
cases this routine will execute more
slowly when a converged solution is
computed. See the section titled "The
Computation of Light Time" in the SPK
Required Reading document spk.req for
'CN+S' Converged Newtonian light time
and stellar aberration corrections.
Light time and stellar aberration
corrections are applied as in the
obsrvr the name of the observing body. This is typically a
spacecraft, the earth, or a surface point on the earth.
[1,c4] = size(obsrvr); char = class(obsrvr)
[1,1] = size(obsrvr); cell = class(obsrvr)
`obsrvr' is case-insensitive, and leading and
trailing blanks in `obsrvr' are not significant.
Optionally, you may supply a string containing the
integer ID code for the object. For example both
'EARTH' and '399' are legitimate strings that indicate
the earth is the observer.
spoint = cspice_subsol( method, target, et, abcorr, obsrvr )
spoint the array(s) describing the sub-solar point on the target
body at 'et', expressed relative to the body-fixed frame
of the target body.
[3,n] = size(rectan); double = class(rectan)
'spoint' returns with the same vectorization measure, N,
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
% Find the sub solar position on the earth as seen from the moon at
% at epoch JAN 1, 2006 using the 'near point' then the 'intercept'
% options. Apply light time correction to return apparent position.
% Load the meta kernel listing the needed SPK, PCK, LSK
cspice_furnsh( 'standard.tm' )
et = cspice_str2et( 'JAN 1, 2006' );
% First use option 'Near Point'
point1 = cspice_subsol( 'near point', 'earth', et, 'lt+s', 'moon');
disp( 'Sub solar location coordinates - near point:' )
fprintf( ' %15.8f\n', point1 )
% Now use option 'Intercept'
point2 = cspice_subsol( 'intercept', 'earth', et, 'lt+s', 'moon');
disp( 'Sub solar location coordinates - intercept' )
fprintf( ' %15.8f\n', point2 )
% Calculate the Euclidean distance between the two locations
% and the angular separation between the position vectors.
dist = norm( point1 - point2);
sep = cspice_vsep(point1, point2 )*cspice_dpr;
fprintf( 'Distance between locations (km): %8.5f\n', dist);
fprintf( 'Angular separation between locations (deg): %8.5f\n', sep );
% It's always good form to unload kernels after use,
% particularly in MATLAB due to data persistence.
Sub solar location coordinates - near point:
Sub solar location coordinates - intercept
Distance between locations (km): 15.38338
Angular separation between locations (deg): 0.13826
cspice_subsol computes the sub-solar point on a target body, as seen by
a specified observer.
There are two different popular ways to define the sub-solar point:
"nearest point on target to the sun" or "target surface intercept of
line containing target and sun." These coincide when the target is
spherical and generally are distinct otherwise.
When comparing sub-point computations with results from sources
other than SPICE, it's essential to make sure the same geometric
definitions are used.
For important details concerning this module's function, please refer to
the CSPICE routine subsol_c.
-Mice Version 1.0.4, 30-OCT-2014, EDW (JPL)
Edited I/O section to conform to NAIF standard for Mice documentation.
-Mice Version 1.0.3, 23-JUN-2014, NJB (JPL)
Updated description of converged Newtonian light time
-Mice Version 1.0.2, 18-MAY-2010, BVS (JPL)
Index line now states that this routine is deprecated.
-Mice Version 1.0.1, 11-NOV-2008, EDW (JPL)
Edits to header; Abstract now states that this routine is
-Mice Version 1.0.0, 07-MAR-2007, EDW (JPL)
DEPRECATED sub-solar point