| phaseq_c |
|
Table of contents
Procedure
phaseq_c ( Phase angle quantity between bodies centers )
SpiceDouble phaseq_c ( SpiceDouble et,
ConstSpiceChar * target,
ConstSpiceChar * illmn,
ConstSpiceChar * obsrvr,
ConstSpiceChar * abcorr )
AbstractCompute the apparent phase angle for a target, observer, illuminator set of ephemeris objects. Required_ReadingNone. KeywordsEPHEMERIS GEOMETRY PHASE ANGLE SEARCH Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- et I Ephemeris seconds past J2000 TDB. target I Target body name. illmn I Illuminating body name. obsrvr I Observer body. abcorr I Aberration correction flag. The function returns the value of phase angle. Detailed_Input
et the time in ephemeris seconds past J2000 TDB at which
to compute the phase angle.
target the name of the target body. 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. The `target' string lack sensitivity to
case, leading and trailing blanks.
illmn the name of the illuminating body. Optionally, you may
supply a string containing the integer ID code
for the object. For example both "SUN" and "10"
are legitimate strings that indicate the sun is the
illuminating body. The `illmn' string lack sensitivity
to case, leading and trailing blanks.
In most cases, `illmn' is the sun.
obsrvr the name of the observer body. 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
observer body. The `obsrvr' string lack sensitivity
to case, leading and trailing blanks.
abcorr the string description of the aberration corrections to
apply to the state evaluations to account for one-way
light time and stellar aberration. The `abcorr' string
lack sensitivity to case, leading and trailing blanks.
This routine accepts only reception mode aberration
corrections. See the header of spkezr_c for a detailed
description of the aberration correction options.
For convenience, the appropriate aberration options are
listed below:
"NONE" Apply no correction. Returns the "true"
geometric state.
"LT" "Reception" case: correct for
one-way light time using a Newtonian
formulation.
"LT+S" "Reception" case: correct for
one-way light time and stellar
aberration using a Newtonian
formulation.
"CN" "Reception" case: converged
Newtonian light time correction.
"CN+S" "Reception" case: converged
Newtonian light time and stellar
aberration corrections.
Detailed_OutputThe function returns the optionally light-time corrected phase angle between `target' and `illmn' as observed from `obsrvr'. The range of the phase angle is [0, pi]. ParametersNone. Exceptions
1) If the body name to SPICE ID look-up fails for any of the
`target', `illmn', or `obsrvr' names, the error
SPICE(IDCODENOTFOUND) is signaled by a routine in the call
tree of this routine.
2) If the aberration correct, `abcorr', indicates a transmission
based correction, the error SPICE(INVALIDOPTION) is signaled
by a routine in the call tree of this routine.
3) If the `target', `illmn', and `obsrvr' are not unique, the error
SPICE(BODIESNOTDISTINCT) is signaled by a routine in the call
tree of this routine.
4) If any of the `target', `illmn', `obsrvr' or `abcorr' input
string pointers is null, the error SPICE(NULLPOINTER) is
signaled. The function returns the value retval.
5) If any of the `target', `illmn', `obsrvr' or `abcorr' input
strings has zero length, the error SPICE(EMPTYSTRING) is
signaled. The function returns the value retval.
FilesNone. Particulars
This routine returns the phase angle using the location of the
bodies (if point objects) or the centers of the bodies (if finite
bodies).
illmn obsrvr
illmn as seen ^ /
from target at | /
et - lt. | /
>|..../< phase angle
| /
. | /
. | /
. |v target as seen from obsrvr
sep . target at et
. /
/
v
pi = sep + phase
so
phase = pi - sep
Examples
The numerical results shown for this example 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) Determine the time intervals from December 1, 2006 UTC to
January 31, 2007 UTC for which the sun-moon-earth configuration
phase angle satisfies the relation conditions with respect to a
reference value of .57598845 radians (the phase angle at
January 1, 2007 00:00:00.000 UTC, 33.001707 degrees). Also
determine the time intervals corresponding to the local maximum and
minimum phase angles, and the absolute maximum and minimum phase
angles during the search interval. The configuration defines the
sun as the illuminator, the moon as the target, and the earth as
the observer.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: phaseq_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
pck00009.tpc Planet orientation and
radii
naif0009.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00009.tpc',
'naif0009.tls' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program phaseq_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"
#define TIMFMT "YYYY MON DD HR:MN:SC.###"
#define NINTVL 5000
#define TIMLEN 41
#define NLOOPS 7
int main()
{
/.
Local variables
./
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SPICEDOUBLE_CELL ( cnfine, 2 );
SPICEDOUBLE_CELL ( result, NINTVL*2 );
SpiceDouble adjust;
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble phaseq;
SpiceDouble refval;
SpiceDouble start;
SpiceDouble step;
SpiceDouble stop;
SpiceInt i;
SpiceInt j;
/.
Define the values for target, observer, illuminator, and
aberration correction.
./
ConstSpiceChar * target = "moon";
ConstSpiceChar * illmn = "sun";
ConstSpiceChar * abcorr = "lt+s";
ConstSpiceChar * obsrvr = "earth";
ConstSpiceChar * relate [NLOOPS] = { "=",
"<",
">",
"LOCMIN",
"ABSMIN",
"LOCMAX",
"ABSMAX" };
/.
Load kernels.
./
furnsh_c ( "phaseq_ex1.tm" );
/.
Store the time bounds of our search interval in
the confinement window.
./
str2et_c ( "2006 DEC 01", &et0 );
str2et_c ( "2007 JAN 31", &et1 );
wninsd_c ( et0, et1, &cnfine );
/.
Search using a step size of 1 day (in units of seconds).
The reference value is 0.57598845 radians. We're not using the
adjustment feature, so we set ADJUST to zero.
./
step = spd_c();
refval = 0.57598845;
adjust = 0.0;
for ( j = 0; j < NLOOPS; j++ )
{
printf ( "Relation condition: %s\n", relate[j] );
/.
Perform the search. The SPICE window `result' contains
the set of times when the condition is met.
./
gfpa_c ( target, illmn, abcorr, obsrvr,
relate[j], refval, adjust, step,
NINTVL, &cnfine, &result );
/.
Display the results.
./
if ( wncard_c(&result) == 0 )
{
printf ( "Result window is empty.\n\n" );
}
else
{
for ( i = 0; i < wncard_c(&result); i++ )
{
/.
Fetch the endpoints of the Ith interval
of the result window.
./
wnfetd_c ( &result, i, &start, &stop );
phaseq = phaseq_c ( start, target, illmn, obsrvr, abcorr );
timout_c ( start, TIMFMT, TIMLEN, begstr );
printf ( "Start time = %s %16.9f\n", begstr, phaseq );
phaseq = phaseq_c ( stop, target, illmn, obsrvr, abcorr );
timout_c ( stop, TIMFMT, TIMLEN, endstr );
printf ( "Stop time = %s %16.9f\n", endstr, phaseq );
}
printf("\n");
}
}
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Relation condition: =
Start time = 2006 DEC 02 13:31:34.414 0.575988450
Stop time = 2006 DEC 02 13:31:34.414 0.575988450
Start time = 2006 DEC 07 14:07:55.470 0.575988450
Stop time = 2006 DEC 07 14:07:55.470 0.575988450
Start time = 2006 DEC 31 23:59:59.997 0.575988450
Stop time = 2006 DEC 31 23:59:59.997 0.575988450
Start time = 2007 JAN 06 08:16:25.512 0.575988450
Stop time = 2007 JAN 06 08:16:25.512 0.575988450
Start time = 2007 JAN 30 11:41:32.557 0.575988450
Stop time = 2007 JAN 30 11:41:32.557 0.575988450
Relation condition: <
Start time = 2006 DEC 02 13:31:34.414 0.575988450
Stop time = 2006 DEC 07 14:07:55.470 0.575988450
Start time = 2006 DEC 31 23:59:59.997 0.575988450
Stop time = 2007 JAN 06 08:16:25.512 0.575988450
Start time = 2007 JAN 30 11:41:32.557 0.575988450
Stop time = 2007 JAN 31 00:00:00.000 0.468279091
Relation condition: >
Start time = 2006 DEC 01 00:00:00.000 0.940714974
Stop time = 2006 DEC 02 13:31:34.414 0.575988450
Start time = 2006 DEC 07 14:07:55.470 0.575988450
Stop time = 2006 DEC 31 23:59:59.997 0.575988450
Start time = 2007 JAN 06 08:16:25.512 0.575988450
Stop time = 2007 JAN 30 11:41:32.557 0.575988450
Relation condition: LOCMIN
Start time = 2006 DEC 05 00:16:50.317 0.086121423
Stop time = 2006 DEC 05 00:16:50.317 0.086121423
Start time = 2007 JAN 03 14:18:31.977 0.079899769
Stop time = 2007 JAN 03 14:18:31.977 0.079899769
Relation condition: ABSMIN
Start time = 2007 JAN 03 14:18:31.977 0.079899769
Stop time = 2007 JAN 03 14:18:31.977 0.079899769
Relation condition: LOCMAX
Start time = 2006 DEC 20 14:09:10.392 3.055062862
Stop time = 2006 DEC 20 14:09:10.392 3.055062862
Start time = 2007 JAN 19 04:27:54.600 3.074603891
Stop time = 2007 JAN 19 04:27:54.600 3.074603891
Relation condition: ABSMAX
Start time = 2007 JAN 19 04:27:54.600 3.074603891
Stop time = 2007 JAN 19 04:27:54.600 3.074603891
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionJ. Diaz del Rio (ODC Space) B.V. Semenov (JPL) E.D. Wright (JPL) Version
-CSPICE Version 1.0.2, 04-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Renamed
example's meta-kernel. Corrected minor formatting issues in
code example.
Added entries #4 and #5 to -Exceptions section.
-CSPICE Version 1.0.1, 02-FEB-2017 (BVS)
Shortened permutted index entry.
-CSPICE Version 1.0.0, 08-MAR-2012 (EDW)
Index_Entriescompute phase angle for arbitrary illumination source |
Fri Dec 31 18:41:10 2021