| Preface - Other Stuff (The Red Shirt topics) (MATLAB) |
Table of ContentsPreface - Other Stuff (The Red Shirt topics) (MATLAB) Coding and Use Lessons Note About HTML Links NAIF Documentation Required Reading and Users Guides Library Source Code Documentation API Documentation Tutorials Text kernels Text kernel format Kernels for lessons Input kernel files Output Lesson 1: Kernel Management with the Kernel Subsystem Relevant Routines Requirements and References Programming Task Code Solution First, create a meta text kernel: Now the solution source code: Run the code example Lesson 2: The Kernel Pool Relevant Routines Requirements and References Programming Task Code Solution Run the code example Lesson 3: Coordinate Conversions Relevant Routines Requirements and References Programming Task Code Solution Run the code example Lesson 4: Advanced Time Manipulation Routines Relevant Routines Requirements and References Programming Task Code Solution Run the code example Lesson 5: Error Handling Relevant Routines: Requirements and References Programming Task Code Solution Run the code example Lesson 6: Windows, and Cells Relevant Routines Requirements and References Programming task: Code Solution Run the code example Lesson 7: Utility and Constants Routines Relevant Routines Requirements and References Programming Task Code Solution Run the code example Programming Task Code Solution Run the code example Preface - Other Stuff (The Red Shirt topics) (MATLAB)
The extensive scope of the Mice system's functionality includes features the average user may not expect or appreciate, features NAIF refers to as "Other Stuff." This workbook includes a set of lessons to introduce the beginning to moderate user to such features. The lessons provide a brief description to several related sets of routines, associated reference documents, a programming task designed to teach the use of the routines, and an example solution to the programming problem. Coding and Use Lessons
Note About HTML Links
In order for the links to be resolved, create a subdirectory called ``lessons'' under the ``doc/html'' directory of the Toolkit tree and copy this document to that subdirectory before loading it into a Web browser. NAIF Documentation
The sources for a user needing information concerning the Mice System or other NAIF product:
Required Reading and Users Guides
cells.req ck.req cspice.req daf.req das.req ek.req ellipses.req error.req frames.req icy.req intrdctn.req kernel.req mice.req naif_ids.req pck.req planes.req problems.req rotation.req scanning.req sclk.req sets.req spc.req spk.req symbols.req time.req windows.reqNAIF Users Guides (*.ug) describe the proper use of particular Mice tools:
brief.ug chronos.ug ckbrief.ug commnt.ug convert.ug inspekt.ug mkspk.ug msopck.ug simple.ug spacit.ug spkdiff.ug spkmerge.ug states.ug subpt.ug tictoc.ug tobin.ug toxfr.ug version.ugThese text documents exist in the 'doc' directory of the main Toolkit directory:
../mice/doc/
HTML format documentation
The Mice distributions include HTML versions of Required Readings and Users Guides, accessible from the HTML documentation directory:
../mice/doc/html/index.html
Library Source Code Documentation
A header consists of several marked sections:
../mice/src/
Find the CSPICE library source code in:
../mice/src/cspice/
Note: The CSPICE source files have two forms: C files created by the f2c
conversion process on a SPICELIB files, indicated with a name of the
form "module.c," and wrappers files indicated by names of the form
"module_c.c" The f2c converted source code is very difficult to read,
refer to the wrapper routines if possible. In some cases, NAIF replaced
an f2c converted file with a hand written version.
API Documentation
...mice/doc/html/cspice/index.html
Also included is Mice Reference Guide, an index of all Mice APIs with
hyperlinks to API specific documentation. Each API documentation page
includes cross-links to any other Mice APIs mentioned in the document
and a link to the API documentation for the CSPICE routine called by the
Mice interface.
...mice/doc/html/mice/index.html
This Mice API documentation (the same information as in the Reference
Guide but without hyperlinks) is also available from the Matlab "help"
command:
>> help cspice_illum -Abstract CSPICE_ILLUM calculates the illumination angles at a specified surface point of a target body. ... Tutorials
http://naif.jpl.nasa.gov/naif/tutorials.html
Access individual files in the 'office/individual_docs/' directory; an
archive of all tutorial files is available in the 'office/packages/'
directory.
Text kernels
The subsystem uses two tags:
\begintext
and
\begindata
to mark information blocks within the text kernel. The \begintext tag
specifies all text following the tag as comment information to be
ignored by the subsystem.
Things to know:
\begintext
... commentary information on the data assignments ...
\begindata
... data assignments ...
Text kernel format
VAR_NAME_DP = 1.234
VAR_NAME_INT = 1234
VAR_NAME_STR = 'FORBIN'
Please note the use of a single quote in string assignments.
Vector assignments. Vectors must contain the same type data.
VEC_NAME_DP = ( 1.234 , 45.678 , 901234.5 )
VEC_NAME_INT = ( 1234 , 456 , 789 )
VEC_NAME_STR = ( 'FORBIN', 'FALKEN', 'ROBUR' )
also
VEC_NAME_DP = ( 1.234,
45.678,
901234.5 )
VEC_NAME_STR = ( 'FORBIN',
'FALKEN',
'ROBUR' )
Time assignments.
TIME_VAL = @31-JAN-2003-12:34:56.798
TIME_VEC = ( @01-DEC-2004, @15-MAR-2004 )
The at-sign character '@' indicates a time string. The pool subsystem
converts the strings to double precision TDB (a numeric value). Please
note, the time strings must not contain embedded blanks. WARNING - a TDB
string is not the same as a UTC string.
The above examples depict direct assignments via the '=' operator. The kernel pool also permits incremental assignments via the '+=' operator. Please refer to the kernels required reading, kernel.req, for additional information. Kernels for lessonsInput kernel files
FILE NAME TYPE DESCRIPTION
----------------------- ---- ----------------------
naif0008.tls LSK Generic LSK
leapseconds.tls LSK The current leapseconds
kernel (naif0008.tls as
of Jan 2006)
de405s.bsp SPK Planet Ephemeris SPK
pck00008.tpc PCK Generic PCK
These SPICE kernels are included in the lesson package available from
the NAIF server at JPL:
ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Lessons/ Output
Lesson 1: Kernel Management with the Kernel Subsystem
This lesson demonstrates use of the kernel subsystem to load, unload, and list loaded kernels. This lesson requires creation of a SPICE meta kernel. Relevant Routines
Requirements and References
Programming Task
Code SolutionFirst, create a meta text kernel:
\begindata
KERNELS_TO_LOAD = ( 'kernels/spk/de405s.bsp',
'kernels/pck/pck00008.tpc',
'kernels/lsk/leapseconds.tls')
\begintext
... or a more generic meta kernel using the PATH_VALUES/PATH_SYMBOLS
functionality to declare path names as variables:
\begintext
Define the paths to the kernel directory. Use the PATH_SYMBOLS
as aliases to the paths.
\begindata
PATH_VALUES = ( 'kernels/lsk',
'kernels/spk',
'kernels/pck' )
PATH_SYMBOLS = ( 'LSK', 'SPK', 'PCK' )
KERNELS_TO_LOAD = ( '$LSK/naif0008.tls',
'$SPK/de405s.bsp',
'$PCK/pck00008.tpc' )
\begintext
Now the solution source code:
function kernel()
%
% Assign the path name of the meta kernel to META.
%
META = 'meta.tm';
%
% Load the meta kernel then use KTOTAL to interrogate the SPICE
% kernel subsystem.
%
cspice_furnsh( META )
count = cspice_ktotal( 'ALL' );
fprintf( 'Kernel count after load: %i\n', count )
%
% Loop over the number of files; interrogate the SPICE system
% with kdata_c for the kernel names and the type. 'found'
% returns a boolean indicating whether any kernel files of
% the specified type were loaded by the kernel subsystem.
% This example ignores checking 'found' as kernels are known
% to be loaded.
%
for i = 1:count
[ file, type, source, handle, found] = cspice_kdata(i, 'ALL');
fprintf( 'File %s\n', file )
fprintf( 'Type %s\n', type )
fprintf( 'Source %s\n\n', source )
end
%
% Unload one kernel then check the count.
%
cspice_unload( '/kernels/gen/spk/de405s.bsp')
count = cspice_ktotal( 'ALL' );
%
% The subsystem should report one less kernel.
%
fprintf( 'Kernel count after one unload : %i\n', count )
%
% Now unload the meta kernel. This action unloads all
% files listed in the meta kernel.
%
cspice_unload( META )
%
% Check the count. Icy should return a count of zero.
%
count = cspice_ktotal( 'ALL');
fprintf( 'Kernel count after meta unload: %i\n', count )
%
% Done. Unload the kernels.
%
cspice_kclear
Run the code example
Kernel count after load: 4
Now the cspice_kdata loop returns the name of each loaded kernel, the
type of kernel (SPK, CK, TEXT, etc.) and the source of the kernel - the
mechanism that loaded the kernel. The source either identifies a meta
kernel, or contains an empty string. An empty source string indicates a
direct load of the kernel with a cspice_furnsh call.
File meta.tm Type META Source File kernels/spk/de405s.bsp Type SPK Source meta.tm File kernels/pck/pck00008.tpc Type TEXT Source meta.tm File kernels/lsk/naif0008.tls Type TEXT Source meta.tm Kernel count after one unload : 3 Kernel count after meta unload: 0 Lesson 2: The Kernel Pool
The lesson demonstrates the Mice system's facility to retrieve different types of data (string, numeric, scalar, array) from the kernel pool. For the code examples, use this generic text kernel (cassini.tm) containing PCK-type data, kernels to load, and example time strings:
\begintext
Ring model data.
\begindata
BODY699_RING1_NAME = 'A Ring'
BODY699_RING1 = (122170.0 136780.0 0.1 0.1 0.5)
BODY699_RING1_1_NAME = 'Encke Gap'
BODY699_RING1_1 = (133405.0 133730.0 0.0 0.0 0.0)
BODY699_RING2_NAME = 'Cassini Division'
BODY699_RING2 = (117580.0 122170.0 0.0 0.0 0.0)
\begintext
The kernel pool recognizes values preceded by '@' as time
values. When read, the kernel subsystem converts these
representations into double precision ephemeris time.
Caution: The kernel subsystem interprets the time strings
identified by '@' as TDB. The same string passed as input
to @STR2ET is processed as UTC.
The three expressions stored in the EXAMPLE_TIMES array represent
the same epoch.
\begindata
EXAMPLE_TIMES = ( @APRIL-1-2004-12:34:56.789,
@4/1/2004-12:34:56.789,
@JD2453097.0242684
)
\begintext
Name the kernels to load. Use path symbols.
\begindata
PATH_VALUES = ('kernels/spk',
'kernels/pck',
'kernels/lsk')
PATH_SYMBOLS = ('SPK' , 'PCK' , 'LSK' )
KERNELS_TO_LOAD = ( '$SPK/de405s.bsp',
'$PCK/pck00008.tpc',
'$LSK/leapseconds.tls')
\begintext
Relevant Routines
Requirements and References
The main references for pool routines are found in the help command or API documentation for the particular routines. Programming Task
Code Solution
function kervar()
%
% Define the max number of kernel variables
% of concern for this examples.
%
N_ITEMS = 20;
%
% Load the example kernel containing the kernel variables.
% The kernels defined in KERNELS_TO_LOAD load into the
% kernel pool with this call.
%
cspice_furnsh( 'cassini.tm' )
%
% Initialize the start value. This values indicates
% index of the first element to return if a kernel
% variable is an array. START = 1 indicates return everything.
% START = 2 indicates return everything but the first element.
%
START = 1;
%
% Set the template for the variable names to find. Let's
% look for all variables containing the string RING.
% Define this with the wildcard template '*RING*'. Note:
% the template '*RING' would match any variable name
% ending with the RING string.
%
tmplate = '*RING*';
%
% We're ready to interrogate the kernel pool for the
% variables matching the template. cspice_gnpool tells us:
%
% 1. Does the kernel pool contain any variables that
% match the template (value of found).
% 2. If so, how many variables?
% 3. The variable names. (cvals, an array of strings)
%
[cvals,found] = cspice_gnpool( tmplate, START, N_ITEMS );
if ( found )
fprintf( 'No. variables matching template: %i\n\n', ...
size(cvals,1) )
else
disp( 'No kernel variables matched template.\n\n' )
return
end
%
% For convenience, convert the character array to a cell of
% strings.
%
cvals = cellstr( cvals );
%
% Okay, now we know something about the kernel pool
% variables of interest to us. Let's find out more...
%
for i=1:size(cvals,1)
%
% Use cspice_dtpool to return the dimension and type,
% C (character) or N (numeric), of each pool
% variable name in the cvals array. We know 'found'
% will have value true.
%
[found, dim, type] = cspice_dtpool( cvals(i) );
disp( cvals(i) )
fprintf( ' No. items: %i Of type: %s\n', dim, type );
%
% Test character equality, 'N' or 'C'.
%
switch type
case 'N'
%
% If 'type' equals 'N', we found a numeric array.
% In this case any numeric array will be an array
% of double precision numbers ('doubles').
% cspice_gdpool retrieves doubles from the
% kernel pool.
%
[dvars,found] = cspice_gdpool( cvals(i), ...
START, ...
N_ITEMS );
fprintf(' Numeric value: %13.6f\n', dvars )
case 'C'
%
% If 'type' equals 'C', we found a string array.
% cspice_gcpool retrieves string values from the
% kernel pool.
%
[cvars,found] = cspice_gcpool( cvals(i), ...
START, ...
N_ITEMS );
for j=1:size(cvars,1)
fprintf(' String value: %s\n', cvars(j,:) )
end
end
disp(' ')
end
%
% Now look at the time variable EXAMPLE_TIMES. Extract this
% value as an array of doubles.
%
[dvars,found] = cspice_gdpool( 'EXAMPLE_TIMES', START, N_ITEMS );
disp( 'EXAMPLE_TIMES' )
fprintf(' Time value: %24.6f\n', dvars)
%
% Done. Unload the kernels.
%
cspice_kclear
Run the code example
No. variables matching template: 6The program then loops over the cspice_dtpool 6 times, reporting the name of each pool variable, the number of data items assigned to that variable, and the variable type. Within the cspice_dtpool loop, a second loop outputs the contents of the data variable using cspice_gcpool or cspice_gdpool.
'BODY699_RING1'
No. items: 5 Of type: N
Numeric value: 122170.000000
Numeric value: 136780.000000
Numeric value: 0.100000
Numeric value: 0.100000
Numeric value: 0.500000
'BODY699_RING2'
No. items: 5 Of type: N
Numeric value: 117580.000000
Numeric value: 122170.000000
Numeric value: 0.000000
Numeric value: 0.000000
Numeric value: 0.000000
'BODY699_RING1_1'
No. items: 5 Of type: N
Numeric value: 133405.000000
Numeric value: 133730.000000
Numeric value: 0.000000
Numeric value: 0.000000
Numeric value: 0.000000
'BODY699_RING1_NAME'
No. items: 1 Of type: C
String value: A Ring
'BODY699_RING2_NAME'
No. items: 1 Of type: C
String value: Cassini Division
'BODY699_RING1_1_NAME'
No. items: 1 Of type: C
String value: Encke Gap
Note the final time value differs from the previous values in the final
three decimal places despite the intention that all three strings
represent the same time. This results from round-off when converting a
decimal Julian day representation to the seconds past J2000 ET
representation.
EXAMPLE_TIMES
Time value: 134094896.789000
Time value: 134094896.789000
Time value: 134094896.789753
Lesson 3: Coordinate Conversions
The Mice system provides functions to convert coordinate tuples between Cartesian and various non Cartesian coordinate systems including conversion between geodetic and rectangular coordinates. This lesson presents these coordinate transform routines for rectangular, cylindrical, and spherical systems. Relevant Routines
Requirements and References
Programming Task
Code Solution
function coord()
%
% Define the inertial and non inertial frame names.
%
% Initialize variables or set type. All variables
% used in a PROMPT construct must be initialized
% as strings.
%
INRFRM = 'J2000';
NONFRM = 'IAU_EARTH';
%
% Load the needed kernels using a cspice_furnsh call on the
% meta kernel.
%
cspice_furnsh( 'meta.tm' )
%
% Prompt the user for a time string. Convert the
% time string to ephemeris time J2000 (ET).
%
timstr = input( 'Time of interest: ', 's' );
et = cspice_str2et( timstr );
%
% Access the kernel pool data for the triaxial radii of the
% Earth, rad[0] holds the equatorial radius, rad[2]
% the polar radius.
%
rad = cspice_bodvrd( 'EARTH', 'RADII', 3 );
%
% Calculate the flattening factor for the Earth.
%
% equatorial_radius - polar_radius
% flat = ________________________________
%
% equatorial_radius
%
flat = (rad(1) - rad(3))/rad(1);
%
% Make the cspice_spkpos call to determine the apparent
% position of the Moon w.r.t. to the Earth at 'et' in the
% inertial frame.
%
[pos, ltime] = cspice_spkpos('MOON', et, INRFRM, 'LT+S','EARTH');
%
% Show the current frame and time.
%
disp( [' Time : ' timstr ] )
disp( [' Inertial Frame: ' INRFRM ] )
%
% First convert the position vector
% X = pos(1), Y = pos(2), Z = pos(3), to RA/DEC.
%
[ range, ra, dec ] = cspice_recrad( pos );
disp(' Range/Ra/Dec' )
fprintf(' Range: %f\n' , range )
fprintf(' RA : %f\n' , ra * cspice_dpr )
fprintf(' DEC : %f\n\n', dec* cspice_dpr )
%
% ...latitudinal coordinates...
%
[ range, lon, lat ] = cspice_reclat( pos );
disp(' Latitudinal ' )
fprintf(' Rad : %f\n' , range )
fprintf(' Lon : %f\n' , lon * cspice_dpr )
fprintf(' Lat : %f\n\n', lat * cspice_dpr )
%
% ...spherical coordinates use the colatitude,
% the angle from the Z axis.
%
[ range, colat, lon ] = cspice_recsph( pos );
disp( ' Spherical' )
fprintf(' Rad : %f\n' , range )
fprintf(' Lon : %f\n' , lon * cspice_dpr )
fprintf(' Colat: %f\n\n', colat * cspice_dpr )
%
% Make the cspice_spkpos call to determine the apparent
% position of the Moon w.r.t. to the Earth at 'et' in the
% non-inertial, body fixed, frame.
%
[pos, ltime] = cspice_spkpos('MOON', et, NONFRM, 'LT+S','EARTH');
disp( [' Non-inertial Frame: ' NONFRM ] )
%
% ...latitudinal coordinates...
%
[ range, lon, lat ] = cspice_reclat( pos );
disp(' Latitudinal ' )
fprintf(' Rad : %f\n' , range )
fprintf(' Lon : %f\n' , lon * cspice_dpr )
fprintf(' Lat : %f\n\n', lat * cspice_dpr )
%
% ...spherical coordinates use the colatitude,
% the angle from the Z axis.
%
[ range, colat, lon ] = cspice_recsph( pos );
disp( ' Spherical' )
fprintf(' Rad : %f\n' , range )
fprintf(' Lon : %f\n' , lon * cspice_dpr )
fprintf(' Colat: %f\n\n', colat * cspice_dpr )
%
% ...finally, convert the position to geodetic coordinates.
%
[ lon, lat, range ] = cspice_recgeo( pos, rad(1), flat );
disp( ' Geodetic' )
fprintf(' Rad : %f\n' , range )
fprintf(' Lon : %f\n' , lon * cspice_dpr )
fprintf(' Lat : %f\n\n', lat * cspice_dpr )
%
% Done. Unload the kernels.
%
cspice_kclear
Run the code example
Time of interest: Feb 3 2002 TDBExamine the Moon position in the J2000 inertial frame, display the time and frame:
Time : Feb 3 2002 TDB
Inertial Frame: J2000
Convert the Moon Cartesian coordinates to right ascension declination.
Range/Ra/Dec
Range: 369340.815193
RA : 203.643686
DEC : -4.979010
Latitudinal. Note the difference in the expressions for longitude and
right ascension though they represent a measure of the same quantity.
The RA/DEC system measures RA in the interval [0,2Pi). Latitudinal
coordinates measures longitude in the interval (-Pi,Pi].
Latitudinal
Rad : 369340.815193
Lon : -156.356314
Lat : -4.979010
Spherical. Note the difference between the expression of latitude in the
Latitudinal system and the corresponding Spherical colatitude. The
spherical coordinate system uses the colatitude, the angle measure away
from the positive Z axis. Latitude is the angle between the position
vector and the x-y (equatorial) plane with positive angle defined as
toward the positive Z direction
Spherical
Rad : 369340.815193
Lon : -156.356314
Colat: 94.979010
The same position look-up in a body fixed (non-inertial) frame,
IAU_EARTH.
Non-inertial Frame: IAU_EARTH
Latitudinal coordinates return the geocentric latitude.
Latitudinal
Rad : 369340.815193
Lon : 70.973950
Lat : -4.989675
Spherical.
Spherical
Rad : 369340.815193
Lon : 70.973950
Colat: 94.989675
Geodetic. The cartographic lat/lon.
Geodetic
Rad : 362962.836755
Lon : 70.973950
Lat : -4.990249
Lesson 4: Advanced Time Manipulation Routines
Introduce the routines used for advanced manipulation of time strings. Understand the concept of ephemeris time (ET) as used in Mice. Relevant Routines
Requirements and References
Also, examine the header of cspice_timout for a list of the string markers used by cspice_timout and cspice_tpictr to describe time string format. Always keep in mind cspice_str2et assumes 'UTC' unless indicated otherwise. Programming Task
Code Solution
function xtic()
%
% Assign the LSK variable to the name of the leapsecond,
% kernel and create an arbitrary time string.
%
% Define the maximum length for any string, 80
% characters plus one null terminator for C.
%
CALSTR = 'Mar 15, 2003 12:34:56.789 AM PST';
LSK = 'kernels/lsk/naif0008.tls';
AMBIGSTR = 'Mar 15, 79 12:34:56';
T_FORMAT1 = 'Wkd Mon DD HR:MN:SC PDT YYYY ::UTC-7';
T_FORMAT2 = 'Wkd Mon DD HR:MN ::UTC-7 YR (JULIAND.##### JDUTC)';
%
% Load the leapseconds kernel.
%
cspice_furnsh( LSK )
disp( [ 'Original time string : ' CALSTR ] )
%
% Convert the time string to the number of ephemeris
% seconds past the J2000 epoch. This is the most common
% internal time representation used by the CSPICE
% system; CSPICE refers to this as ephemeris time (ET).
%
et = cspice_str2et( CALSTR );
fprintf( 'Corresponding ET : %13.6f\n', et )
%
% Make a picture of an output format. Describe a Unix-like
% time string then send the picture and the 'et' value through
% cspice_timout to format and convert the ET representation
% of the time string into the form described in cspice_timout.
% The '::UTC-7' token indicates the time zone for the 'timstr'
% output - PDT. 'PDT' is part of the output, but not a time
% system token.
%
timstr = cspice_timout( et, T_FORMAT1);
fprintf( 'Time in string format 1 : %s\n', timstr )
timstr = cspice_timout( et, T_FORMAT2);
fprintf( 'Time in string format 2 : %s\n', timstr )
%
% Why create a picture by hand when Mice can do it for you?
% Input a string to cspice_tpictr with the format of interest.
% 'ok' returns a boolean indicating whether an error occurred
% while parsing the picture string, if so, an error diagnostic
% message returns in 'xerror'. In this example the picture
% string is known as correct.
%
pic = '12:34:56.789 P.M. PDT January 1, 2006';
[ pictr, ok, xerror] = cspice_tpictr(pic);
if ( ~ok )
error( xerror )
end
timstr = cspice_timout( et, pictr);
fprintf( 'Time in string format 3 : %s\n', timstr )
%
% Two digit year representations often cause problems due to
% the ambiguity of the century. The routine cspice_tsetyr gives
% the user the ability to set a default range for 2 digit year
% representation. SPICE uses 1969AD as the default start
% year so the numbers inclusive of 69 to 99 represent years
% 1969AD to 1999AD, the numbers inclusive of 00 to 68 represent
% years 2000AD to 2068AD.
%
% The defined time string 'AMBIGSTR' contains a two-digit
% year. Since the SPICE base year is 1969, the time subsystem
% interprets the string as 1979.
%
et1 = cspice_str2et( AMBIGSTR );
%
% Set 1980 as the base year causes SPICE to interpret the
% time string's "79" as 2079.
%
cspice_tsetyr( 1980 )
et2 = cspice_str2et( AMBIGSTR );
%
% Calculate the number of years between the two ET
% representations, ~100.
%
fprintf( 'Years between evaluations : %16.6f\n', ...
(et2 - et1)/cspice_jyear )
%
% Reset the default year to 1969.
%
cspice_tsetyr( 1969 )
%
% Done. Unload the kernels.
%
cspice_kclear
Run the code example
Original time string : Mar 15, 2003 12:34:56.789 AM PST Corresponding ET : 100989360.974561 Time in string format 1 : Sat Mar 15 01:34:56 PDT 2003 Time in string format 2 : Sat Mar 15 01:34 03 (2452713.85760 JDUTC) Time in string format 3 : 01:34:56.789 A.M. PDT March 15, 2003 Years between evaluations : 100.000000 Lesson 5: Error Handling
The Mice error subsystem differs from CSPICE and SPICELIB packages in that the user cannot alter the state of the error subsystem, rather the user can respond to an error signal using try-catch blocks. This block natively receives and processes any SPICE error signaled from Mice. The user can therefore "catch" an error signal so as to respond in an appropriate manner. Relevant Routines:
Requirements and References
Programming Task
Code Solution
function aderr()
%
% Set initial parameters.
%
SPICETRUE = logical(1);
SPICEFALSE= logical(0);
doloop = SPICETRUE;
%
% Load the data we need for state evaluation.
%
cspice_furnsh( 'meta.tm' )
%
% Start our input query loop to the user.
%
while (doloop)
%
% For simplicity, we request only one input.
% The program calculates the state vector from
% Earth to the user specified target 'targ' in the
% J2000 frame, at ephemeris time zero, using
% aberration correction LT+S (light time plus
% stellar aberration).
%
targ = input( 'Target: ', 's' );
if ( strcmpi( targ, 'NONE') )
%
% An exit condition. If the user inputs NONE
% for a target name, set the loop to stop...
%
doloop = SPICEFALSE;
else
%
% ...otherwise evaluate the state between the Earth
% and the target. Initialize an error handler.
%
try
%
% Perform the state lookup.
%
[ state, ltime] = cspice_spkezr( targ, 0., 'J2000', ...
'LT+S' , ...
'EARTH');
%
% No error, output the state.
%
fprintf( 'R : %17.5f %17.5f %17.5f\n', state(1:3)' )
fprintf( 'V : %17.5f %17.5f %17.5f\n', state(4:6)' )
fprintf( 'LT: %f\n\n', ltime )
catch
%
% What if cspice_spkezr signaled an error?
% Then Mice signals an error to MATLAB.
%
% Examine the value of 'lasterr' to retrieve the
% error message.
%
disp( lasterr )
disp(' ')
end
end
end
%
% Done. Unload the kernels.
%
cspice_kclear
Run the code example
Target: Moon R : -291584.61659 -266693.40236 -76095.64756 V : 0.64353 -0.66608 -0.30132 LT: 1.342311 Target: Mars R : 234536077.41914 -132584383.59557 -63102685.70619 V : 30.95976 28.93646 13.11449 LT: 923.001080 Target: Pluto barycenter R : -1451304742.83853 -4318174144.40632 -918251433.58736 V : 35.03838 3.06560 -0.01514 LT: 15501.258293 Target: Puck SPICE(SPKINSUFFDATA): [spkezr_c->SPKEZR->SPKEZ->SPKAPP->SPKSSB-> SPKGEO] Insufficient ephemeris data has been loaded to compute the state of 715 (PUCK) relative to 0 (SOLAR SYSTEM BARYCENTER) at the ephemeris epoch 2000 JAN 01 12:00:00.000.Perplexing. What happened? The kernel files named in meta.tm did not include ephemeris data for Puck. When the SPK subsystem tried to evaluate Puck's position, the evaluation failed due to lack of data, so an error signaled. The above error signifies an absence of state information at ephemeris time 2000 JAN 01 12:00:00.000 (the requested time, ephemeris time zero). Try another look-up.
Target: Casper SPICE(IDCODENOTFOUND): [spkezr_c->SPKEZR] The target, 'Casper', is not a recognized name for an ephemeris object. The cause of this problem may be that you need an updated version of the SPICE Toolkit. Alternatively you may call SPKEZ directly if you know the SPICE ID codes for both 'Casper' and 'EARTH'An easy to understand error. The SPICE system does not contain information on a body named 'Casper.' Another look-up, this time, something easy.
Target: Venus R : -80970027.54053 -139655772.57390 -53860125.95820 V : 31.16969 -27.00018 -12.31622 LT: 567.655074The look-up succeeded despite two errors in our run. The Mice system can respond to error conditions (not system errors) in much the same fashion as languages with catch/throw instructions. Lesson 6: Windows, and Cells
This lesson introduces the concepts of the SPICE data type 'window'. The Mice implementation of a SPICE windows consists of double precision Nx1 arrays with N an even or zero value. A 'window' is a type of cell containing ordered, double precision values describing a collection of zero or more intervals. We define an interval, 'i', as all double precision values bounded by and including an ordered pair of numbers,
[ a , b ]
i i
where
a < b
i - i
The intervals within a window are both ordered and disjoint. That is,
the beginning of each interval is greater than the end of the previous
interval:
b < a
i i+1
A common use of the windows facility is to calculate the intersection
set of a number of time intervals.
Relevant Routines
Requirements and References
Programming task:
Code Solution
function win
%
% The windows hold 8 data, i.e. values four intervals.
%
MAXSIZ = 8;
%
% Define a set of time intervals. For the purposes of this
% tutorial program, define time intervals representing
% an unobscured line of sight between a ground station
% and some body.
%
los = { 'Jan 1, 2003 22:15:02', 'Jan 2, 2003 4:43:29', ...
'Jan 4, 2003 9:55:30', 'Jan 4, 2003 11:26:52', ...
'Jan 5, 2003 11:09:17', 'Jan 5, 2003 13:00:41', ...
'Jan 6, 2003 00:08:13', 'Jan 6, 2003 2:18:01' };
%
% A second set of intervals representing the times for which
% an acceptable phase angle exits between the ground station,
% the body and the Sun.
%
phase = { 'Jan 2, 2003 00:03:30', 'Jan 2, 2003 19:00:00', ...
'Jan 3, 2003 8:00:00', 'Jan 3, 2003 9:50:00', ...
'Jan 5, 2003 12:00:00', 'Jan 5, 2003 12:45:00', ...
'Jan 6, 2003 00:30:00', 'Jan 6, 2003 23:00:00' };
%
% Load our meta kernel for the leapseconds data.
%
cspice_furnsh( 'meta.tm' )
%
% SPICE windows consist of double precision values; convert
% the string time tags defined in the 'los'and 'phase'
% arrays to double precision ET. Store the double values
% in the 'loswin' and 'phswin' windows.
%
los_et = cspice_str2et( los );
phs_et = cspice_str2et( phase );
%
% Initialize the windows with the 'los_et' and 'phs_et'
% values.
%
% Create two empty windows.
%
loswin = zeros(0,1);
phswin = zeros(0,1);
%
% Mice windows lack a constant size as the windows interfaces
% dynamically adjust window size before return, therefore the
% SPICE concept of window cardinality degenerates to window size.
%
for i=1:(MAXSIZ/2)
loswin = cspice_wninsd( los_et(2*i - 1), los_et(2*i), loswin );
phswin = cspice_wninsd( phs_et(2*i - 1), phs_et(2*i), phswin );
end
%
% The issue for consideration, at what times do line of
% sight events coincide with acceptable phase angles?
% Perform the set operation AND on loswin, phswin,
% (the intersection of the time intervals)
% place the results in the window 'sched'.
%
sched = cspice_wnintd( loswin, phswin);
%
% Output the results. The number of intervals in 'sched'
% is half the number of data points (the cardinality).
%
card = numel(sched);
fprintf( 'No. data values in sched : %i\n\n', card )
fprintf( 'Time intervals meeting defined criterion.\n' )
for i=1:(card/2)
%
% Extract from the derived 'sched' the values defining the
% time intervals.
%
[left, right ] = cspice_wnfetd( sched, i );
%
% Convert the ET values to UTC for human comprehension.
%
utcstr_l = cspice_et2utc( left , 'C', 3 );
utcstr_r = cspice_et2utc( right, 'C', 3 );
%
% Output the UTC string and the corresponding index
% for the interval.
%
fprintf( '%i %s %s\n', i, utcstr_l, utcstr_r )
end
Run the code example
Output the amount of data held in 'sched'.
No. data values in sched : 6
List the time intervals for which a line of sight exists during the time
of a proper phase angle.
Time intervals meeting defined criterion. 1 2003 JAN 02 00:03:30.000 2003 JAN 02 04:43:29.000 2 2003 JAN 05 12:00:00.000 2003 JAN 05 12:45:00.000 3 2003 JAN 06 00:30:00.000 2003 JAN 06 02:18:01.000 Lesson 7: Utility and Constants Routines
Mice provides several routines to perform commonly needed tasks. Among these:
Relevant Routines
Requirements and References
Programming Task
Code Solution
function units()
%
% Display the Toolkit version string with a
% cspice_tkvrsn call.
%
vers = cspice_tkvrsn( 'TOOLKIT' );
disp( ['Convert demo program compiled against CSPICE Toolkit ' ...
vers] )
%
% The user first inputs the name of a unit of measure.
% Send the name through TOSTAN for de-aliasing.
%
funits = input( 'From Units : ', 's' );
funits = tostan( funits );
%
% Input a double precision value to express in a new
% unit format.
%
fvalue = input( 'From Value : ' );
%
% Now the user inputs the name of the output units.
% Again we send the units name through TOSTAN for
% de-aliasing.
%
tunits = input( 'To Units : ', 's' );
tunits = tostan( tunits );
tvalue = cspice_convrt( fvalue, funits, tunits );
fprintf( '%f %s\n', tvalue, tunits )
function value = tostan( alias )
value = alias;
%
% As a convenience, let's alias a few common terms
% to their appropriate counterpart. Use strcmpi
% to compare strings. The comparison ignores
% letter case and trailing/leading spaces. NOTE: the SWITCH
% statement performs the same function as the multiple
% 'if' blocks. SWITCH was not used in order to demonstrate
% the strcmpi call.
%
if ( strcmpi( alias, 'meter') )
%
% First, a 'meter' by any other name is a
% 'METER' and smells as sweet ...
%
value = 'METERS';
elseif ( strcmpi( alias, 'klicks' ) || ...
strcmpi( alias, 'kilometers') || ...
strcmpi( alias, 'kilometer' ) )
%
% ... 'klicks' and 'KILOMETERS' and 'KILOMETER'
% identifies 'KM'....
%
value = 'KM';
elseif ( strcmpi( alias, 'secs') )
%
% ... 'secs' to 'SECONDS'.
%
value = 'SECONDS';
elseif ( strcmpi( alias, 'miles') )
%
% ... and finally 'miles' to 'STATUTE_MILES'.
% Normal people think in statute miles.
% Only sailors think in nautical miles - one
% minute of arc at the equator.
%
value = 'STATUTE_MILES';
end
%
% Much better. Now return. If the input matched
% none of the aliases, this function did nothing.
%
Run the code example
Convert demo program compiled against CSPICE Toolkit CSPICE_N0061 From Units : klicks From Value : 3 To Units : miles 1.864114 STATUTE_MILESNow we know. Three kilometers equals 1.864 miles. Legend states Pheidippides ran from the Marathon Plain to Athens. The modern marathon race (inspired by this event) spans 26.2 miles. How far in kilometers?
Convert demo program compiled against CSPICE Toolkit CSPICE_N0061 From Units : miles From Value : 26.2 To Units : km 42.164813 km Programming Task
Code Solution
function xconst();
%
% All the function have the same calling sequence:
%
% VALUE = function_name
%
% some_procedure( function_name )
%
% First a simple example using the seconds per day
% constant...
%
fprintf( ...
'Number of (S)econds (P)er (D)ay : %19.12f\n', ...
cspice_spd )
%
% ...then show the value of degrees per radian, 180/Pi...
%
fprintf( ...
'Number of (D)egrees (P)er (R)adian : %19.12f\n', ...
cspice_dpr )
%
% ...and the inverse, radians per degree, Pi/180.
% It is obvious cspice_dpr() equals 1.d/cspice_rpd(), or
% more simply cspice_dpr() * cspice_rpd() equals 1
%
fprintf( ...
'Number of (R)adians (P)er (D)egree : %19.12f\n', ...
cspice_rpd )
%
% What's the value for the astrophysicist's favorite
% physical constant (in a vacuum)?
%
fprintf( ...
'Speed of light in KM per second : %19.12f\n', ...
cspice_clight )
%
% How long (in Julian days) from the J2000 epoch to the
% J2100 epoch?
%
fprintf( ...
'Number of days between epochs J2000/J2100 : %19.12f\n', ...
cspice_j2100 - cspice_j2000 )
%
% Redo the calculation returning seconds...
%
fprintf( ...
'Number of seconds between epochs : %19.5f\n', ...
cspice_spd * (cspice_j2100 - cspice_j2000 ) )
fprintf( ...
' J2000/J2100 :\n')
%
% ...then tropical years.
%
fprintf( ...
'Number of tropical years between epochs : %19.12f\n', ...
(cspice_spd/cspice_tyear) * (cspice_j2100- spice_j2000 ) )
fprintf( ...
' J2000/J2100 :\n')
%
% Finally, how can I convert a radian value to degrees.
%
fprintf( ...
'Number of degrees in Pi/2 radians of arc : %19.12f\n', ...
cspice_halfpi * cspice_dpr )
%
% and degrees to radians.
%
fprintf( ...
'Number of radians in 250 degrees of arc : %19.12f\n', ...
250. * cspice_rpd )
Run the code example
Number of (S)econds (P)er (D)ay : 86400.000000000000
Number of (D)egrees (P)er (R)adian : 57.295779513082
Number of (R)adians (P)er (D)egree : 0.017453292520
Speed of light in KM per second : 299792.457999999984
Number of days between epochs J2000/J2100 : 36525.000000000000
Number of seconds between epochs : 3155760000.000000
J2000/J2100 :
Number of tropical years between epochs : 100.002135902909
J2000/J2100 :
Number of degrees in Pi/2 radians of arc : 90.000000000000
Number of radians in 250 degrees of arc : 4.363323129986
|