Table of contents
CSPICE_OCCULT determines the occultation condition (not occulted,
partially occulted, etc.) of one target relative to another target as
seen by an observer at a given time.
The surfaces of the target bodies may be represented by triaxial
ellipsoids, points, or by topographic data provided by DSK files.
Given:
targ1 the name of the first target body.
[1,c1] = size(targ1); char = class(targ1)
or
[1,1] = size(targ1); cell = class(targ1)
Both object names and NAIF IDs are accepted. For example,
both 'Moon' and '301' are accepted.
shape1 a string indicating the geometric model used to represent the
shape of the first target body.
[1,c2] = size(shape1); char = class(shape1)
or
[1,1] = size(shape1); cell = class(shape1)
The supported options are:
'ELLIPSOID'
Use a triaxial ellipsoid model with radius
values provided via the kernel pool. A kernel
variable having a name of the form
'BODYnnn_RADII'
where nnn represents the NAIF integer code
associated with the body, must be present in
the kernel pool. This variable must be
associated with three numeric values giving the
lengths of the ellipsoid's X, Y, and Z
semi-axes.
'POINT'
Treat the body as a single point. When a point
target is specified, the occultation conditions
can only be total, annular, or none.
'DSK/UNPRIORITIZED[/SURFACES = <surface list>]'
Use topographic data provided by DSK files to
model the body's shape. These data must be
provided by loaded DSK files.
The surface list specification is optional. The
syntax of the list is
<surface 1> [, <surface 2>...]
If present, it indicates that data only for the
listed surfaces are to be used; however, data
need not be available for all surfaces in the
list. If absent, loaded DSK data for any surface
associated with the target body are used.
The surface list may contain surface names or
surface ID codes. Names containing blanks must
be delimited by double quotes, for example
SURFACES = "Mars MEGDR 128 PIXEL/DEG"
If multiple surfaces are specified, their names
or IDs must be separated by commas.
See the -Particulars section below for details
concerning use of DSK data.
The combinations of the shapes of the target bodies
`targ1' and `targ2' must be one of:
One ELLIPSOID, one POINT
Two ELLIPSOIDs
One DSK, one POINT
Case and leading or trailing blanks are not
significant in the string `shape1'.
frame1 the name of the body-fixed, body-centered reference frame
associated with the first target body.
[1,c3] = size(frame1); char = class(frame1)
or
[1,1] = size(frame1); cell = class(frame1)
Examples of such names are 'IAU_SATURN' (for Saturn) and
'ITRF93' (for the Earth).
If the first target body is modeled as a point, `frame1'
should be left blank (Ex: ' ').
Case and leading or trailing blanks bracketing a
non-blank frame name are not significant in the string.
targ2 the name of the second target body.
[1,c4] = size(targ2); char = class(targ2)
or
[1,1] = size(targ2); cell = class(targ2)
See the description of `targ1' above for more details.
shape2 the shape specification for the body designated by `targ2'.
[1,c5] = size(shape2); char = class(shape2)
or
[1,1] = size(shape2); cell = class(shape2)
See the description of `shape1' above for details.
frame2 the name of the body-fixed, body-centered reference frame
associated with the second target body.
[1,c6] = size(frame2); char = class(frame2)
or
[1,1] = size(frame2); cell = class(frame2)
See the description of `frame1' above for more details.
abcorr indicates the aberration corrections to be applied to the
state of each target body to account for one-way light time.
[1,c7] = size(abcorr); char = class(abcorr)
or
[1,1] = size(abcorr); cell = class(abcorr)
Stellar aberration corrections are ignored if specified,
since these corrections don't improve the accuracy of the
occultation determination.
See the header of the Mice routine cspice_spkezr for a
detailed description of the aberration correction
options. For convenience, the options supported by
this routine are listed below:
'NONE' Apply no correction.
'LT' "Reception" case: correct for
one-way light time using a Newtonian
formulation.
'CN' "Reception" case: converged
Newtonian light time correction.
'XLT' "Transmission" case: correct for
one-way light time using a Newtonian
formulation.
'XCN' "Transmission" case: converged
Newtonian light time correction.
Case and blanks are not significant in the string
`abcorr'.
obsrvr the name of the body from which the occultation is observed.
[1,c8] = size(obsrvr); char = class(obsrvr)
or
[1,1] = size(obsrvr); cell = class(obsrvr)
See the description of `targ1' above for more details.
et the observation time(s) in seconds past the J2000 epoch.
[1,n] = size(et); double = class(et)
the call:
[ocltid] = cspice_occult( targ1, shape1, frame1, ...
targ2, shape2, frame2, ...
abcorr, obsrvr, et )
returns:
ocltid an integer occultation code(s) indicating the geometric
relationship of the three bodies.
[1,n] = size(ocltid); int32 = class(ocltid)
The meaning of the sign of `ocltid' is given below.
Code sign Meaning
--------- ------------------------------
> 0 The second target is
partially or fully occulted
by the first.
< 0 The first target is
partially of fully
occulted by the second.
= 0 No occultation.
Possible `ocltid' values and meanings are given below. The
variable names indicate the type of occultation and which
target is in the back. For example, SPICE_OCCULT_TOTAL1
represents a total occultation in which the first target is in
the back of (or is occulted by) the second target.
When the target shapes are DSK and POINT, the only
possible occultation conditions are total, annular,
or none.
Name Code Meaning
------------------- ----- -----------------------
SPICE_OCCULT_TOTAL1 -3 Total occultation of
first target by second.
SPICE_OCCULT_ANNLR1 -2 Annular occultation of
first target by second.
The second target does
not block the limb of
the first.
SPICE_OCCULT_PARTL1 -1 Partial occultation of
first target by second
target.
SPICE_OCCULT_NOOCC 0 No occultation or
transit: both objects
are completely visible
to the observer.
SPICE_OCCULT_PARTL2 1 Partial occultation of
second target by first
target.
SPICE_OCCULT_ANNLR2 2 Annular occultation of
second target by first.
SPICE_OCCULT_TOTAL2 3 Total occultation of
second target by first.
None.
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.
1) Find whether MRO is occulted by Mars as seen by
the DSS-13 ground station at a few specific
times.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File: occult_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
pck00010.tpc Planet orientation and
radii
naif0010.tls Leapseconds
earth_latest_high_prec.bpc Earth latest binary PCK
earthstns_itrf93_050714.bsp DSN station SPK
mro_psp22.bsp MRO ephemeris
earth_topo_050714.tf Topocentric reference
frames for DSN
stations
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'mro_psp22.bsp',
'earthstns_itrf93_050714.bsp',
'earth_latest_high_prec.bpc',
'pck00010.tpc',
'naif0010.tls',
'earth_topo_050714.tf' )
\begintext
End of meta-kernel.
Example code begins here.
function occult_ex1()
%
% MiceUser is a file that makes occultation-specific
% variables global. You must call MiceUser to have access to
% these variable names. These variables are defined so you don't
% need to remember what the integer codes mean that the
% occultation routine returns. For more information, please see
% MiceUser.m and MiceOccult.m.
%
MiceUser;
targ1 = 'MRO';
shape1 = 'point';
targ2 = 'Mars';
shape2 = 'ellipsoid';
observer = 'DSS-13';
dt = 1000;
out_form = '%s %s %s %s wrt %s\n';
out_char = ['totally occulted by ';
'transited by ';
'partially occulted by';
'not occulted by '];
%
% Load the meta kernel.
%
cspice_furnsh ( 'occult_ex1.tm' );
et_start = cspice_str2et ( '2012-jan-5 1:15:00 UTC' );
et_stop = cspice_str2et ( '2012-jan-5 2:50:00 UTC' );
for et = et_start : dt : et_stop
%
% Calculate the type of occultation that
% corresponds to time ET.
%
ocltid = cspice_occult ( targ1, shape1, ' ', ...
targ2, shape2, 'iau_mars', ...
'cn', observer, et );
%
% Output the results.
%
time = cspice_timout ( et, 'YYYY-MM-DD HR:MN ::UTC-8');
%
% Remember: You must call 'MiceUser' before
% using the parameters like 'SPICE_OCCULT_TOTAL1' in
% the case statements below.
%
switch ocltid
case SPICE_OCCULT_TOTAL1
fprintf (out_form, time, targ1, out_char(1,:), ...
targ2, observer )
case SPICE_OCCULT_ANNLR1
fprintf (out_form, time, targ1, out_char(2,:), ...
targ2, observer )
case SPICE_OCCULT_PARTL1
fprintf (out_form, time, targ1, out_char(3,:), ...
targ2, observer )
case SPICE_OCCULT_NOOCC
fprintf (out_form, time, targ1, out_char(4,:), ...
targ2, observer )
case SPICE_OCCULT_PARTL2
fprintf (out_form, time, targ2, out_char(3,:), ...
targ1, observer )
case SPICE_OCCULT_ANNLR2
fprintf (out_form, time, targ2, out_char(2,:), ...
targ1, observer )
case SPICE_OCCULT_TOTAL2
fprintf (out_form, time, targ2, out_char(1,:), ...
targ1, observer )
otherwise
fprintf ( 'Bad occultation code: %d\n', ocltid )
end
end
%
% Unload kernels
%
cspice_kclear
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
2012-01-04 17:15 Mars transited by MRO wrt DSS-13
2012-01-04 17:31 MRO not occulted by Mars wrt DSS-13
2012-01-04 17:48 MRO totally occulted by Mars wrt DSS-13
2012-01-04 18:04 MRO totally occulted by Mars wrt DSS-13
2012-01-04 18:21 MRO not occulted by Mars wrt DSS-13
2012-01-04 18:38 Mars transited by MRO wrt DSS-13
For many purposes, modeling extended bodies as triaxial
ellipsoids is adequate for determining whether one body is
occulted by another as seen from a specified observer.
Using DSK data
==============
DSK loading and unloading
-------------------------
DSK files providing data used by this routine are loaded by
calling cspice_furnsh and can be unloaded by calling cspice_unload or
cspice_kclear. See the documentation of cspice_furnsh for limits on
numbers of loaded DSK files.
For run-time efficiency, it's desirable to avoid frequent
loading and unloading of DSK files. When there is a reason to
use multiple versions of data for a given target body---for
example, if topographic data at varying resolutions are to be
used---the surface list can be used to select DSK data to be
used for a given computation. It is not necessary to unload
the data that are not to be used. This recommendation presumes
that DSKs containing different versions of surface data for a
given body have different surface ID codes.
DSK data priority
-----------------
A DSK coverage overlap occurs when two segments in loaded DSK
files cover part or all of the same domain---for example, a
given longitude-latitude rectangle---and when the time
intervals of the segments overlap as well.
When DSK data selection is prioritized, in case of a coverage
overlap, if the two competing segments are in different DSK
files, the segment in the DSK file loaded last takes
precedence. If the two segments are in the same file, the
segment located closer to the end of the file takes
precedence.
When DSK data selection is unprioritized, data from competing
segments are combined. For example, if two competing segments
both represent a surface as a set of triangular plates, the
union of those sets of plates is considered to represent the
surface.
Currently only unprioritized data selection is supported.
Because prioritized data selection may be the default behavior
in a later version of the routine, the UNPRIORITIZED keyword is
required in the `shape1' and `shape2' arguments.
Syntax of the shape input arguments for the DSK case
----------------------------------------------------
The keywords and surface list in the target shape arguments
`shape1' and `shape2' are called "clauses." The clauses may
appear in any order, for example
'DSK/<surface list>/UNPRIORITIZED'
'DSK/UNPRIORITIZED/<surface list>'
'UNPRIORITIZED/<surface list>/DSK'
The simplest form of the `method' argument specifying use of
DSK data is one that lacks a surface list, for example:
'DSK/UNPRIORITIZED'
For applications in which all loaded DSK data for the target
body are for a single surface, and there are no competing
segments, the above string suffices. This is expected to be
the usual case.
When, for the specified target body, there are loaded DSK
files providing data for multiple surfaces for that body, the
surfaces to be used by this routine for a given call must be
specified in a surface list, unless data from all of the
surfaces are to be used together.
The surface list consists of the string
'SURFACES = '
followed by a comma-separated list of one or more surface
identifiers. The identifiers may be names or integer codes in
string format. For example, suppose we have the surface
names and corresponding ID codes shown below:
Surface Name ID code
------------ -------
"Mars MEGDR 128 PIXEL/DEG" 1
"Mars MEGDR 64 PIXEL/DEG" 2
"Mars_MRO_HIRISE" 3
If data for all of the above surfaces are loaded, then
data for surface 1 can be specified by either
'SURFACES = 1'
or
'SURFACES = "Mars MEGDR 128 PIXEL/DEG"'
Double quotes are used to delimit the surface name because
it contains blank characters.
To use data for surfaces 2 and 3 together, any
of the following surface lists could be used:
'SURFACES = 2, 3'
'SURFACES = "Mars MEGDR 64 PIXEL/DEG", 3'
'SURFACES = 2, Mars_MRO_HIRISE'
'SURFACES = "Mars MEGDR 64 PIXEL/DEG", Mars_MRO_HIRISE'
An example of a shape argument that could be constructed
using one of the surface lists above is
'DSK/UNPRIORITIZED/SURFACES = "Mars MEGDR 64 PIXEL/DEG", 3'
1) If the target or observer body names input by the user are
not recognized, an error is signaled by a routine in
the call tree of this routine.
2) If the input shapes are not accepted, an error is signaled by
a routine in the call tree of this routine.
3) If both input shapes are points, an error is signaled by a
routine in the call tree of this routine.
4) If the radii of a target body modeled as an ellipsoid cannot
be determined by searching the kernel pool for a kernel
variable having a name of the form
'BODYnnn_RADII'
where nnn represents the NAIF integer code associated with
the body, an error is signaled by a routine in the
call tree of this routine.
5) If any of the target or observer bodies (targ1, targ2, or
obsrvr) are the same, an error is signaled
by a routine in the call tree of this routine.
6) If the loaded kernels provide insufficient data to compute any
required state vector, an error is signaled by a routine in
the call tree of this routine.
7) If an error occurs while reading an SPK or other kernel,
the error is signaled by a routine in the call tree
of this routine.
8) If the aberration correction specification `abcorr' is invalid,
an error is signaled by a routine in the call tree of this
routine.
9) If either `shape1' or `shape2' specifies that the target surface
is represented by DSK data, and no DSK files are loaded for
the specified target, an error is signaled by a routine in
the call tree of this routine.
10) If either `shape1' or `shape2' specifies that the target surface
is represented by DSK data, but the shape specification is
invalid, an error is signaled by a routine in the call tree
of this routine.
11) If any of the input arguments, `targ1', `shape1', `frame1',
`targ2', `shape2', `frame2', `abcorr', `obsrvr' or `et', is
undefined, an error is signaled by the Matlab error handling
system.
12) If any of the input arguments, `targ1', `shape1', `frame1',
`targ2', `shape2', `frame2', `abcorr', `obsrvr' or `et', is
not of the expected type, or it does not have the expected
dimensions and size, an error is signaled by the Mice
interface.
Appropriate SPICE kernels must be loaded by the calling program
before this routine is called.
The following data are required:
- SPK data: the calling application must load ephemeris data
for the target, source and observer that cover the time
instant specified by the argument `et'. If aberration
corrections are used, the states of the target bodies and of
the observer relative to the solar system barycenter must be
calculable from the available ephemeris data. Typically
ephemeris data
are made available by loading one or more SPK files via
cspice_furnsh.
- PCK data: bodies modeled as triaxial ellipsoids must have
semi-axis lengths provided by variables in the kernel pool.
Typically these data are made available by loading a text
PCK file via cspice_furnsh.
- FK data: if either of the reference frames designated by
`frame1' or `frame2' are not built in to the SPICE system,
one or more FKs specifying these frames must be loaded.
The following data may be required:
- DSK data: if either `shape1' or `shape2' indicates that DSK
data are to be used, DSK files containing topographic data
for the target body must be loaded. If a surface list is
specified, data for at least one of the listed surfaces must
be loaded.
- Surface name-ID associations: if surface names are specified
in `shape1' or `shape2', the association of these names with
their corresponding surface ID codes must be established by
assignments of the kernel variables
NAIF_SURFACE_NAME
NAIF_SURFACE_CODE
NAIF_SURFACE_BODY
Normally these associations are made by loading a text
kernel containing the necessary assignments. An example
of such a set of assignments is
NAIF_SURFACE_NAME += 'Mars MEGDR 128 PIXEL/DEG'
NAIF_SURFACE_CODE += 1
NAIF_SURFACE_BODY += 499
- CK data: either of the body-fixed frames to which `frame1' or
`frame2' refer might be a CK frame. If so, at least one CK
file will be needed to permit transformation of vectors
between that frame and the J2000 frame.
- SCLK data: if a CK file is needed, an associated SCLK
kernel is required to enable conversion between encoded SCLK
(used to time-tag CK data) and barycentric dynamical time
(TDB).
Kernel data are normally loaded once per program run, NOT every
time this routine is called.
None.
MICE.REQ
DSK.REQ
None.
N.J. Bachman (JPL)
J. Diaz del Rio (ODC Space)
S.C. Krening (JPL)
E.D. Wright (JPL)
-Mice Version 2.1.0, 03-NOV-2021 (EDW) (JDR)
Changed argument names "target1", "target2", "observer", "time" and
"occult_code" to "targ1", "targ2", "obsrvr", "et" and "ocltid" for
consistency with other functions.
Edited the header to comply with NAIF standard. Added square brackets
to output argument in function declaration.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections.
Eliminated use of "lasterror" in rethrow.
Removed reference to the function's corresponding CSPICE header from
-Required_Reading section.
-Mice Version 2.0.0, 04-APR-2017 (EDW) (NJB)
Header update to reflect support for use of DSKs.
-Mice Version 1.0.0, 14-NOV-2013 (SCK)
occultation type at a specified time
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