| Preface - Other Stuff (The Red Shirt topics) (C) |
Table of ContentsPreface - Other Stuff (The Red Shirt topics) (C) 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 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) (C)
The extensive scope of the CSPICE 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 CSPICE 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 CSPICE 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:
../cspice/doc/
HTML format documentation
The CSPICE distributions include HTML versions of Required Readings and Users Guides, accessible from the HTML documentation directory:
../cspice/doc/html/index.html
Library Source Code Documentation
A header consists of several marked sections:
../cspice/src/
Find the CSPICE library source code in:
../cspice/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
...cspice/doc/html/cspice/index.html
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:
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/*
Define the maximum length for any string, 80
characters plus one null terminator.
*/
#define LENOUT 81
int main( int argc, char **argv )
{
/* Declare the needed variables: */
SpiceChar file [LENOUT];
SpiceChar type [LENOUT];
SpiceChar source [LENOUT];
SpiceInt i;
SpiceInt count;
SpiceInt handle;
SpiceBoolean found;
/* Assign the path name of the meta kernel to META. */
SpiceChar * META = "meta.tm";
/*
Load the meta kernel then use KTOTAL to interrogate the SPICE
kernel subsystem for the total number of loaded kernel files.
*/
furnsh_c ( META );
ktotal_c ("ALL", &count );
printf( "Kernel count after load: %ld\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 = 0L; i < count; i++ )
{
kdata_c( i, "ALL", LENOUT, LENOUT, LENOUT,
file, type, source, &handle, &found );
printf ( "File %s\n", file );
printf ( "Type %s\n", type );
printf ( "Source %s\n", source );
printf ( "\n" );
}
/*
Unload one kernel then check the count.
*/
unload_c ( "kernels/spk/de405s.bsp" );
ktotal_c ( "ALL", &count );
/*
The subsystem should report one less kernel.
*/
printf ( "Kernel count after one unload: %ld\n", count );
/*
Now unload the meta kernel. This action unloads all
files listed in the meta kernel.
*/
unload_c ( META );
/*
Check the count. SPICE should return a count of zero.
*/
ktotal_c ( "ALL", &count );
printf ( "Kernel count after meta unload: %ld\n", count );
exit(0);
}
Run the code example
Kernel count after load: 4
Now the kdata_c 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 furnsh_c 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 CSPICE 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 source files or API documentation for the particular routines. Programming Task
Code Solution
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/*
Define the max number of kernel variables
of concern for this examples.
*/
#define N_ITEMS 20
/*
Define the maximum length for any string, 80
characters plus one null terminator.
*/
#define STRLEN 81
int main( int argc, char **argv )
{
/*
Note, the pool routines return a boolean to 'found'
signaling whether the requested variable name exists
in the kernel pool. The code solutions do not check the
boolean value since the solutions use variables known to
exist. In general, code should always check the boolean
value to ensure return of valid data.
*/
/*
As usual, type our variables...
*/
SpiceInt i;
SpiceInt j;
SpiceInt dim;
SpiceInt n_var;
SpiceInt n_val;
SpiceInt start;
SpiceBoolean found;
SpiceDouble dvars [N_ITEMS];
SpiceChar cvals [N_ITEMS][STRLEN];
SpiceChar cvars [N_ITEMS][STRLEN];
SpiceChar type;
SpiceChar tmplate[12];
/*
Load the example kernel containing the kernel variables.
The kernels defined in KERNELS_TO_LOAD load into the
kernel pool with this call.
*/
furnsh_c ( "cassini.tm" );
/*
Initialize the start value. This values indicates
index of the first element to return if a kernel
variable is an array. start = 0 indicates return everything.
start = 1 indicates return everything but the first element.
*/
start = 0;
/*
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.
*/
strcpy ( tmplate, "*RING*");
/*
We're ready to interrogate the kernel pool for the
variables matching the template. gnpool_c tells us:
1. Does the kernel pool contain any variables that
match the template (value of found).
2. If so, how many variables? (value of n_val)
3. The variable names. (cvals, an array of strings)
*/
gnpool_c ( tmplate, start, N_ITEMS, STRLEN,
&n_val, cvals, &found );
if ( found )
{
printf( "No. variables matching template: %ld\n", n_val);
}
else
{
puts ( "No kernel variables matched template" );
exit(0);
}
/*
Okay, now we know something about the kernel pool
variables of interest to us. Let's find out more...
*/
for (i=0; i<n_val; ++i )
{
/*
Use dtpool_c to return the dimension and type,
C (character) or N (numeric), of each pool
variable name in the cvals array.
*/
dtpool_c ( cvals[i], &found, &dim, &type );
printf ( "\n%s\n", cvals[i]);
printf ( "No. items: %ld Of type: %c\n\n", dim, type );
/*
Use the EQSTR routine to test character equality,
'N' or 'C'.
*/
if ( type == '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"). gdpool_c
retrieves doubles from the kernel pool. 'dvars'
contains the array of 'n_vars' values.
*/
gdpool_c ( cvals[i], start, N_ITEMS, &n_var,
dvars , &found );
for( j=0; j<n_var; ++j )
{
printf( " Numeric value: %f\n", dvars[j] );
}
}
else if ( type == 'C' )
{
/*
If 'type' equals "C", we found a string array.
gcpool_c retrieves string values from the
kernel pool. cvars[i] contains the array of 'n_var'
values.
*/
gcpool_c ( cvals[i], start , N_ITEMS,
STRLEN , &n_var, cvars , &found );
for( j=0; j<n_var; ++j )
{
printf( " String value: %s\n", cvars[j] );
}
}
}
puts( " " );
/*
Now look at the kernel variable EXAMPLE_TIMES. Extract this
value as an array of doubles.
*/
gdpool_c ( "EXAMPLE_TIMES", start, N_ITEMS, &n_var, dvars,
&found );
puts( "EXAMPLE_TIMES");
for( j=0; j<n_var; ++j )
{
printf( " Time value: %f\n", dvars[j] );
}
exit(0);
}
Run the code example
No. variables matching template: 6The program then loops over the dtpool_c 6 times, reporting the name of each pool variable, the number of data items assigned to that variable, and the variable type. Within the dtpool_c loop, a second loop outputs the contents of the data variable using gcpool_c or gdpool_c.
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 CSPICE 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
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/* Define the length of the time string, 32
characters plus 1 for the null terminator.
*/
#define LENOUT 33
int main( int argc, char **argv )
{
/*
Type the variables.
*/
SpiceInt dim;
/*
Define the inertial and non inertial frame names.
*/
SpiceChar inrfrm [] = "J2000";
SpiceChar nonfrm [] = "IAU_EARTH";
SpiceChar timstr [LENOUT];
SpiceDouble et;
SpiceDouble range;
SpiceDouble ra;
SpiceDouble dec;
SpiceDouble lat;
SpiceDouble colat;
SpiceDouble lon;
SpiceDouble ltime;
SpiceDouble flat;
SpiceDouble rad [3];
SpiceDouble pos [3];
/*
Load the needed kernels using a furnsh_c call on the
meta kernel.
*/
furnsh_c ( "meta.tm" );
/*
Prompt the user for a time string. Convert the
time string to ephemeris time J2000 (ET).
*/
prompt_c ( "Time of interest: ", LENOUT, timstr );
str2et_c ( timstr, &et );
/*
Access the kernel pool data for the triaxial radii of the
Earth, 'rad[0]' holds the equatorial radius, 'rad[2]'
the polar radius.
*/
bodvrd_c ( "Earth", "RADII", 3, &dim, rad);
/*
Calculate the flattening factor for the Earth.
equatorial_radius - polar_radius
flat = ________________________________
equatorial_radius
*/
flat = (rad[0] - rad[2])/rad[0];
/*
Make the spkpos_c call to determine the apparent position of
the Moon w.r.t. to the Earth at 'et' in the inertial frame.
*/
spkpos_c ( "MOON", et, inrfrm, "LT+S","EARTH", pos, <ime);
/*
Show the current frame and time.
*/
printf ( " Time : %s\n" , timstr );
printf ( " Inertial Frame: %s\n", inrfrm );
/*
First convert the position vector
X = pos[0], Y = pos[1], Z = pos[2], to RA/DEC.
*/
recrad_c ( pos, &range, &ra, &dec );
printf ( " Range/Ra/Dec\n" );
printf ( " Range: %f\n", range );
printf ( " RA : %f\n", ra * dpr_c() );
printf ( " DEC : %f\n", dec* dpr_c() );
/*
...latitudinal coordinates...
*/
reclat_c ( pos, &range, &lon, &lat );
printf ( " Latitudinal\n" );
printf ( " Rad : %f\n", range);
printf ( " Lon : %f\n", lon * dpr_c() );
printf ( " Lat : %f\n", lat * dpr_c() );
/*
...spherical coordinates use the colatitude,
the angle from the Z axis.
*/
recsph_c ( pos, &range, &colat, &lon );
printf ( " Spherical\n");
printf ( " Rad : %f\n", range );
printf ( " Lon : %f\n", lon * dpr_c() );
printf ( " Colat: %f\n", colat * dpr_c() );
/*
Make the spkpos_c call to determine the apparent position of
the Moon w.r.t. to the Earth at 'et' in the non-inertial,
body fixed, frame.
*/
spkpos_c ( "MOON", et, nonfrm, "LT+S","EARTH", pos, <ime);
puts ( " " );
printf ( " Non-inertial Frame: %s\n", nonfrm );
/*
...latitudinal coordinates...
*/
reclat_c ( pos, &range, &lon, &lat );
printf ( " Latitudinal\n" );
printf ( " Rad : %f\n", range );
printf ( " Lon : %f\n", lon * dpr_c() );
printf ( " Lat : %f\n", lat * dpr_c() );
/*
...spherical coordinates...
*/
recsph_c ( pos, &range, &colat, &lon );
printf ( " Spherical\n" );
printf ( " Rad : %f\n", range );
printf ( " Lon : %f\n", lon * dpr_c() );
printf ( " Colat: %f\n", colat * dpr_c() );
/*
...finally, convert the position to geodetic coordinates.
*/
recgeo_c ( pos, rad[0], flat, &lon, &lat, &range );
printf ( " Geodetic\n" );
printf ( " Rad : %f\n", range );
printf ( " Lon : %f\n", lon * dpr_c() );
printf ( " Lat : %f\n", lat * dpr_c() );
puts ( " " );
exit(0);
}
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 : 70.986950
Lat : -4.989675
Spherical.
Spherical
Rad : 369340.815193
Lon : 70.986950
Colat: 94.989675
Geodetic. The cartographic lat/lon.
Geodetic
Rad : 362962.836755
Lon : 70.986950
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 CSPICE. Relevant Routines
Requirements and References
Also, examine the header of timout_c for a list of the string markers used by timout_c and tpictr_c to describe time string format. Always keep in mind str2et_c assumes 'UTC' unless indicated otherwise. Programming Task
Code Solution
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/*
Define the maximum length for any string, 80
characters plus one null terminator.
*/
#define STRLEN 256
int main( int argc, char **argv )
{
/* Declare the needed variables: */
SpiceDouble et;
SpiceDouble et1;
SpiceDouble et2;
SpiceBoolean ok;
SpiceChar error [STRLEN];
SpiceChar pictr [STRLEN];
SpiceChar timstr[STRLEN];
/*
Assign the LSK variable to the name of the leapsecond,
kernel and create an arbitrary time string.
*/
SpiceChar * CALSTR =
"Mar 15, 2003 12:34:56.789 AM PST";
SpiceChar * LSK =
"/kernels/gen/lsk/leapseconds.tls";
SpiceChar * AMBIGSTR =
"Mar 15, 79 12:34:56";
/* Load the leapseconds kernel. */
furnsh_c ( LSK );
printf ( "Original time string : %s\n", 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).
*/
str2et_c ( CALSTR, &et );
printf ( "Corresponding ET : %f\n", et );
/*
Make a picture of an output format. Describe a Unix-like
time string then send the picture and the 'et' value through
timout_c to format and convert the ET representation of the
time string into the form described in timout_c. 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.
*/
timout_c ( et,
"Wkd Mon DD HR:MN:SC PDT YYYY ::UTC-7",
STRLEN,
timstr );
printf ( "Time in string format 1 : %s\n", timstr );
/*
Create another picture, this time combine a calendar,
2 digit year , with Julian Day format.
*/
timout_c ( et,
"Wkd Mon DD HR:MN ::UTC-7 YR (JULIAND.##### JDUTC)",
STRLEN,
timstr );
printf ( "Time in string format 2 : %s\n", timstr );
/*
Why create a picture by hand when CSPICE can do it for you?
Input a string to tpictr_c 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 'error'. In this
example, no need exists to check the error flag since
the picture string is known as correct..
*/
tpictr_c ( "12:34:56.789 P.M. PDT January 1, 2006",
STRLEN,
STRLEN,
pictr,
&ok,
error);
/*
Confirm the tpictr_c call succeeded. Report the error string
if not.
*/
if( !ok )
{
printf( "\nError in TPICTR call:\n" );
printf( "%s\n", error );
exit(1);
}
timout_c ( et, pictr, STRLEN, timstr );
printf ("Time in string format 3 : %s\n", timstr );
/*
Two digit year representations often cause problems due to
the ambiguity of the century. The routine tsetyr_c 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.
*/
str2et_c ( AMBIGSTR, &et1 );
/*
Set 1980 as the base year causes CSPICE to interpret the time
string's "79" as 2079.
*/
tsetyr_c ( 1980 );
str2et_c ( AMBIGSTR, &et2 );
/*
Calculate the number of years between the two ET
representations, ~100.
*/
printf ( "Years between evaluations : %f\n",
(et2 - et1)/jyear_c() );
exit(0);
}
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
This lesson introduces the basics of the error subsystem and its various the response modes: DEFAULT, RETURN, ABORT, RETURN, IGNORE, the error output modes: SHORT, LONG, EXPLAIN TRACEBACK, DEFAULT, ALL, NONE, and the error traceback message. Relevant Routines:
Requirements and References
Programming Task
Code Solution
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/*
Define the maximum length for any string, 80
characters plus one null terminator.
*/
#define STRLEN 81
void doerr();
int main( int argc, char **argv )
{
/* Declare the needed variables: */
SpiceChar errcon[STRLEN];
SpiceBoolean doloop = SPICETRUE;
/*
Check into the error subsystem to create a traceback
showing the call tree. A chkout_c must balance every
chkin_c.
*/
chkin_c ( "ERRSYSC" );
/*
Before we start, what's the initial (default)
error state? erract_c both sets the state and
reports the state.
*/
erract_c ( "GET", STRLEN, errcon );
printf ( "Default error state: %s\n", errcon );
/*
Now start an input loop so we can try different
settings for error response.
*/
do
{
/* Again use ERRACT to retrieve the current error mode. */
erract_c ( "GET", STRLEN, errcon );
printf ( "Current error state: %s\n", errcon );
/*
Okay, input one of the response settings strings
then set the error subsystem response to that value.
*/
prompt_c ( "Set error condition (DEFAULT, REPORT, "
"ABORT, RETURN, IGNORE) :",
STRLEN,
errcon );
erract_c ( "SET", STRLEN, errcon );
/* Cause an error signal. */
doerr();
/*
Check for an error signal via a call to FAILED.
At this point we see an important difference
between the error mode's response to an error
signal.
*/
if ( !failed_c() )
{
puts( "No error signal noted." );
}
else
{
puts( "Error signal noted." );
}
}
while ( doloop );
/*
Check out of the error subsystem tho' we'll
never hit this call.
*/
chkout_c ( "ERRSYSC" );
exit(0);
}
/* This subroutine initiates a SPICE error signal. */
void doerr ()
{
/* Check into the error subsystem as before. */
chkin_c ("DOERR");
/*
Let's signal an error. The string passed by setmsg_c
is the long error message. You may place markers in the
long message string then later substitute other data
items for those markers.
*/
setmsg_c ( "A truly horrendous event occurred "
"during execution of this program. "
"Data added to long error message string: "
"A double #, an int #, and a string #." );
/*
Now substitute other data into the long message string.
Note the substitutions work on the first found marker.
*/
errdp_c ( "#", 186282.397 );
errint_c ( "#", 666 );
errch_c ( "#", "A STRING" );
/*
SIGERR causes the error signal with the string passed
from SETMSG. Set the error flag in the SPICE error
subsystem and execute the proper error response.
*/
sigerr_c ( "OOPS(SOMETHINGBAD)" );
chkout_c ( "DOERR" );
}
Run the code example
Default error state: DEFAULT Current error state: DEFAULTThe subsystem is in error state DEFAULT. Let the subsystem run to the error signal in DEFAULT mode:
Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE):defaultWhat subsystem reaction occurs in this state?
=================================================================== Toolkit version: N0060 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. Data added to long error message string: A double 1.8628239700000E+05, an int 666, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSF --> DOERR Oh, by the way: The SPICELIB error handling actions are USER-TAILORABLE. You can choose whether the Toolkit aborts or continues when errors occur, which error messages to output, and where to send the output. Please read the ERROR "Required Reading" file, or see the routines ERRACT, ERRDEV, and ERRPRT. ===================================================================Notice we see no error signal status line. The program quit when it signaled an error. The program output the error messages, an additional information blurb ("Oh by the way"), the Toolkit version, and the traceback list. o- Rerun the program in REPORT mode:
Default error state: DEFAULT
Current error state: DEFAULT
Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE) :report
===================================================================
Toolkit version: N0060
OOPS(SOMETHINGBAD) --
A truly horrendous event occurred during execution of this program.
Data added to long error message string: A double
1.8628239700000E+05, an int 666, and a string A STRING.
A traceback follows. The name of the highest level module is
first. ERRSYSF --> DOERR
===================================================================
Error signal noted.
Current error state: REPORT
Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE) :
The error output ceases after the traceback then returns into the
calling routine. Note the error signal marker indicates detection of the
signal. The subsystem in REPORT mode does not print the information
blurb. The CSPICE system can continue to run after an error signal with
the error state set to REPORT - this mode flags an error then allows the
program to continue the run. It may happen that the cause of the error
condition causes instability in the CSPICE system.
o- Rerun to test ABORT mode:
Default error state: DEFAULT Current error state: DEFAULT Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :abortHow does the subsystem respond in ABORT mode?
=================================================================== Toolkit version: N0060 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. Data added to long error message string: A double 1.8628239700000E+05, an int 666, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSF --> DOERR ===================================================================ABORT responds quite like DEFAULT except the error output does not include the information blurb shown in the DEFAULT output. All execution stops when the error signals. o- Run the program to demo the RETURN mode:
Default error state: DEFAULT Current error state: DEFAULT Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :returnRETURN mode provides the highest measure of flexibility to deal with error signals. On output:
===================================================================
Toolkit version: N0060
OOPS(SOMETHINGBAD) --
A truly horrendous event occurred during execution of this program.
Data added to long error message string: A double
1.8628239700000E+05, an int 666, and a string A STRING.
A traceback follows. The name of the highest level module is first.
ERRSYSF --> DOERR
===================================================================
Error signal noted.
Current error state: RETURN
The subroutine signals an error then returns similar to REPORT mode.
However, this mode includes another property. If we make another pass
through the command loop:
Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE):return Error signal noted. Current error state: RETURNWe see no error output. The main property of the RETURN mode is to allow program execution to continue but immediately return from all CSPICE routines that check the state of the return_c function. This mode restricts program flow after an error signal. o- And the final mode to test, IGNORE:
Default error state: DEFAULT Current error state: DEFAULT Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :ignore No error signal noted. Current error state: IGNORE Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :No error output, no error signal. IGNORE mode prevents expression of all error subsystem functions; the subsystem does not set RETURN or FAILED. While using IGNORE mode the user cannot identify an error signal. Carefully consider program requirements before any use of IGNORE mode. Programming Task
Code Solution
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
/*
Define the maximum length for any string, 80
characters plus one null terminator.
*/
#define STRLEN 81
int main( int argc, char **argv )
{
/* Declare the needed variables: */
SpiceChar targ [STRLEN];
/*
Set a flag to start/stop and continue the
inquiry loop.
*/
SpiceBoolean doloop = SPICETRUE;
SpiceDouble state[6];
SpiceDouble ltime;
/*
The RETURN mode signals an error then returns to the
caller. Just what we need. REPORT mode performs almost
the same function as RETURN, however RETURN mode
sets the return_c() value to TRUE and so the program does
not execute those CSPICE routines that check the return_c()
value. Consider REPORT mode useful for debugging.
*/
erract_c ( "SET", STRLEN, "RETURN" );
/*
Load the data we need for state evaluation.
*/
furnsh_c ( "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).
*/
prompt_c ( "Target: ", STRLEN, targ );
if ( eqstr_c( 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.
*/
spkezr_c ( targ, 0., "J2000", "LT+S", "EARTH", state,
<ime );
/*
What if the program can't perform the evaluation?
Since we set the error subsystem to REPORT we know
a failed spkezr_c call sets the failed_c flag to
SPICETRUE then returns control to the calling routine.
The CSPICE system also outputs an error message
informing the user of the problem's cause.
Examine the state of failed_c() to determine if we
output a state vector or not.
*/
if ( ! failed_c() )
{
printf ( "R : %17.5f %17.5f %17.5f\n",
state[0] , state[1], state[2] );
printf ( "V : %17.5f %17.5f %17.5f\n",
state[3] , state[4], state[5] );
printf ( "LT: %f\n", ltime );
}
else
{
/*
Problem. Something went wrong. Reset the error
subsystem for another pass.
*/
reset_c();
}
}
}
exit(0);
}
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 =================================================================== Toolkit version: N0060 SPICE(SPKINSUFFDATA) -- 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. A traceback follows. The name of the highest level module is first. spkezr_c --> SPKEZR --> SPKEZ --> SPKAPP --> SPKSSB --> SPKGEO ===================================================================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). Since the program set the error mode to RETURN, program execution continues. Try another look-up.
Target: Casper =================================================================== Toolkit version: N0060 SPICE(IDCODENOTFOUND) -- 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' A traceback follows. The name of the highest level module is first. spkezr_c --> SPKEZR ===================================================================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 CSPICE 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 types 'cell' and 'window'. A 'cell' is a data structure designed to provide easy and safe manipulation of typed array data. A C SPICE cell consists of a C structure. A user should create cells by use of the appropriate CSPICE calls. NAIF recommends against manual creation of cells. 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
#include <stdio.h>
#include "SpiceUsr.h"
#include <stdlib.h>
#include <string.h>
#define MAXSIZ 8
/*
Define the maximum length for a UTC string, 25
characters plus one null terminator.
*/
#define UTCLEN 26
int main( int argc, char **argv )
{
/*
Define our variable types.
Define the cells to use as windows.
The windows can hold 8 data values i.e.
four intervals.
*/
SPICEDOUBLE_CELL ( loswin, MAXSIZ );
SPICEDOUBLE_CELL ( phswin, MAXSIZ );
SPICEDOUBLE_CELL ( sched , MAXSIZ );
SpiceInt i;
SpiceInt small;
SpiceInt large;
SpiceChar utcstr[2][UTCLEN];
/*
Define sets 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.
*/
SpiceChar los [MAXSIZ][UTCLEN] =
{ "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.
*/
SpiceChar phase [MAXSIZ][UTCLEN] =
{ "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"
};
SpiceDouble left;
SpiceDouble right;
SpiceDouble meas;
SpiceDouble avg;
SpiceDouble stddev;
SpiceDouble los_et [MAXSIZ];
SpiceDouble phs_et [MAXSIZ];
/* Load our meta kernel for the leapseconds data. */
furnsh_c ( "meta.tm" );
/*
Windows consist of double precision values, convert the
time tags defined in the LOS and PHASE arrays to
double precision ET. Store the double values in the
loswin and phswin arrays.
*/
for ( i=0; i < MAXSIZ; ++i )
{
str2et_c ( los[i] , &los_et[i] );
str2et_c ( phase[i], &phs_et[i] );
}
/*
Initialize the cells from the double precision arrays,
then validate the cells as windows.
Since we use 4 intervals, set the window to accept 8 (MAXSIZ)
data values ( 4 * 2 = 8 ). Since we require no more than
8 data values, assign a window size of 8.
*/
memmove ( (SpiceDouble*)loswin.data,
los_et,
MAXSIZ * sizeof(SpiceDouble) );
memmove ( (SpiceDouble*)phswin.data,
phs_et,
MAXSIZ * sizeof(SpiceDouble) );
wnvald_c ( MAXSIZ, MAXSIZ, &loswin );
wnvald_c ( MAXSIZ, MAXSIZ, &phswin );
wnvald_c ( MAXSIZ, MAXSIZ, &sched );
/*
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,
place the results in the window 'sched'.
*/
wnintd_c ( &loswin, &phswin, &sched );
puts ( " " );
printf ( "No. data values in sched : %d\n",
(int)card_c(&sched) );
printf ( "Space available for values in sched : %d\n",
(int)size_c(&sched) );
/*
Output the results. The number of intervals in 'sched'
is half the number of data points (the cardinality).
Use a call to card_c to retrieve the window's cardinality.
*/
puts ( " " );
puts ( "Time intervals meeting defined criterion.");
for ( i=0; i < card_c(&sched)/2 ; ++i )
{
/*
Extract from the derived 'sched' the values defining the
time intervals, [small, large].
*/
wnfetd_c ( &sched, i, &left, &right );
/*
Convert the ET values to UTC for human comprehension.
*/
et2utc_c ( left , "C", 3, UTCLEN, utcstr[0] );
et2utc_c ( right, "C", 3, UTCLEN, utcstr[1] );
/*
Output the UTC string and the corresponding index
for the interval.
*/
printf ( " %d %s %s\n", (int)i, utcstr[0], utcstr[1] );
}
puts ( " " );
puts ( "Summary of sched window" );
wnsumd_c ( &sched, &meas, &avg, &stddev, &small, &large );
/*
Summarize the 'sched' window.
*/
printf( "o Total measure of sched : %12.5f\n", meas );
printf( "o Average measure of sched : %12.5f\n", avg );
printf( "o Standard deviation of\n " );
printf( " the measures in sched : %12.5f\n", stddev );
/*
The values for small and large refer to the indexes of the
values in the window ('sched'). The shortest interval is
[ SPICE_CELL_ELEM_D( &sched, small),
SPICE_CELL_ELEM_D( &sched, small+1) ];
the longest is
[ SPICE_CELL_ELEM_D( &sched, large),
SPICE_CELL_ELEM_D( &sched, large+1) ];
Output the indexes for the shortest and longest
intervals. As C bases an array index on 0, the interval
index is half the array index.
*/
printf ( "o Index of shortest interval: %d\n", (int)small/2 );
printf ( "o Index of longest interval : %d\n", (int)large/2 );
exit (0);
}
Run the code example
Output the amount of data held in SCHED compared to the maximum possible amount.
No. data values in SCHED : 6
Space available for values in SCHED : 8
List the time intervals for which a line of sight exists during the time
of a proper phase angle.
Time intervals meeting defined criterion.
0 2003 JAN 02 00:03:30.000 2003 JAN 02 04:43:29.000
1 2003 JAN 05 12:00:00.000 2003 JAN 05 12:45:00.000
2 2003 JAN 06 00:30:00.000 2003 JAN 06 02:18:01.000
Finally, an analysis of the SCHED data. The measure of an interval [a,b]
(a <= b) equals b-a. Real values output in units of seconds.
Summary of sched window
o Total measure of sched : 25980.00001
o Average measure of sched : 8660.00000
o Standard deviation of
the measures in sched : 5958.55022
o Index of shortest interval: 1
o Index of longest interval : 0
Lesson 7: Utility and Constants Routines
CSPICE provides several routines to perform commonly needed tasks. Among these:
Relevant Routines
Requirements and References
Programming Task
Code Solution
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SpiceUsr.h"
#define UTCLEN 32
void tostan ( SpiceChar * alias );
int main( int argc, char **argv )
{
/*
Define the few variables needed for data input
and output.
*/
SpiceChar funits [UTCLEN];
SpiceChar tunits [UTCLEN];
SpiceChar fromstr[UTCLEN];
SpiceDouble fvalue;
SpiceDouble tvalue;
/*
Define the tkvrsn_c return value.
*/
ConstSpiceChar * vers;
/*
Display the Toolkit version string with a
tkvrsn_c call.
*/
vers = tkvrsn_c( "TOOLKIT" );
printf( "\n Convert demo program compiled against "
"CSPICE Toolkit %s\n\n", vers );
/*
The user first inputs the name of a unit of measure.
Send the name through TOSTAN for de-aliasing.
*/
prompt_c ( "From Units : ", UTCLEN, funits );
tostan ( funits );
/*
Input a double precision value to express in a new
unit format.
*/
prompt_c ( "From Value : ", UTCLEN, fromstr );
prsdp_c ( fromstr, &fvalue );
/*
Now the user inputs the name of the output units.
Again we send the units name through TOSTAN for
de-aliasing.
*/
prompt_c ( "To Units : ", UTCLEN, tunits );
tostan ( tunits );
convrt_c ( fvalue, funits, tunits, &tvalue );
printf ( "%f %s\n", tvalue, tunits );
exit(0);
}
void tostan ( SpiceChar * alias )
{
/*
As a convenience, let's alias a few common terms
to their appropriate counterpart. Use eqstr_c
to compare strings. The comparison ignores
letter case and trailing/leading spaces.
*/
if ( eqstr_c ( alias, "meter" ) )
{
/*
First, a 'meter' by any other name is a
'METER' and smells as sweet ...
*/
strcpy ( alias, "METERS");
}
else if ( eqstr_c ( alias, "klicks" ) ||
eqstr_c ( alias, "kilometers" ) ||
eqstr_c ( alias, "kilometer" ) )
{
/*
... 'klicks' and 'KILOMETERS' and
'KILOMETER' identifies 'KM'....
*/
strcpy ( alias, "KM");
}
else if ( eqstr_c ( alias, "secs") )
{
/*
... 'secs' to 'SECONDS'.
*/
strcpy ( alias, "SECONDS");
}
else if ( eqstr_c ( 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.
*/
strcpy ( alias, "STATUTE_MILES");
}
/*
Much better. Now return. If the input matched
none of the aliases, this routine did nothing.
*/
}
Run the code example
Convert demo program compiled against CSPICE Toolkit CSPICE_N0060
From Units : klicks
From Value : 3
To Units : miles
1.864114 STATUTE_MILES
Now 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_N0060
From Units : miles
From Value : 26.2
To Units : km
42.164813 km
Programming Task
Code Solution
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include "SpiceUsr.h"
int main( int argc, char **argv )
{
/*
All the functions have the same calling sequence:
VALUE = function_name();
some_procedure( function_name() );
printf ( "%19.12f\n", function_name() );
First a simple example using the seconds per day
constant...
*/
printf ("Number of (S)econds (P)er (D)ay : %19.12f\n",
spd_c() );
/*
...then show the value of degrees per radian, 180/Pi...
*/
printf ("Number of (D)egrees (P)er (R)adian : %19.16f\n",
dpr_c() );
/*
...and the inverse, radians per degree, Pi/180.
It is obvious dpr_c() equals 1.0/rpd_c(), or more simply
dpr_c() * rpd_c() equals 1.0.
*/
printf("Number of (R)adians (P)er (D)egree : %19.16f\n",
rpd_c() );
/*
What's the value for the astrophysicist's favorite
physical constant (in a vacuum)?
*/
printf ("Speed of light in KM per second : %19.12f\n",
clight_c() );
/*
How long (in Julian days) from the J2000 epoch to the
J2100 epoch?
*/
printf ("Number of days between epochs J2000 \n" );
printf (" and J2100 : %19.12f\n",
j2100_c() - j2000_c() );
/*
Redo the calculation returning seconds...
*/
printf ("Number of seconds between epochs\n" );
printf (" J2000 and J2100 : %19.5f\n",
spd_c() * (j2100_c() - j2000_c() ) );
/*
...then tropical years.
*/
printf ( "Number of tropical years between\n" );
printf ( " epochs J2000 and J2100 : %19.12f\n",
( spd_c() / tyear_c() ) * (j2100_c() - j2000_c() ) );
/*
Finally, how can I convert a radian value to degrees.
*/
printf ("Number of degrees in Pi/2 radians of arc : %19.16f\n",
halfpi_c() * dpr_c() );
/*
and degrees to radians.
*/
printf ("Number of radians in 250 degrees of arc : %19.16f\n",
250. * rpd_c() );
exit(0);
}
Run the code example
Number of (S)econds (P)er (D)ay : 86400.000000000000
Number of (D)egrees (P)er (R)adian : 57.2957795130823229
Number of (R)adians (P)er (D)egree : 0.0174532925199433
Speed of light in KM per second : 299792.457999999984
Number of days between epochs J2000
and J2100 : 36525.000000000000
Number of seconds between epochs
J2000 and J2100 : 3155760000.00000
Number of tropical years between
epochs J2000 and J2100 : 100.002135902909
Number of degrees in Pi/2 radians of arc : 90.0000000000000000
Number of radians in 250 degrees of arc : 4.3633231299858242
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