Other Stuff (C) |
Table of ContentsOther Stuff (C) Overview Note About HTML Links References Tutorials Required Readings The Permuted Index API Documentation Kernels Used CSPICE Modules Used NAIF Documentation Required Reading and Users Guides HTML format documentation Library Source Code Documentation API Documentation Text kernels Text kernel format Lesson 1: Kernel Management with the Kernel Subsystem Task Statement Learning Goals Code Solution First, create a meta text kernel: Now the solution source code: Run the code example Lesson 2: The Kernel Pool Task Statement Learning Goals Code Solution Run the code example Related Routines Lesson 3: Coordinate Conversions Task Statement Learning Goals Code Solution Run the code example Related Routines Lesson 4: Advanced Time Manipulation Routines Task Statement Learning Goals Code Solution Run the code example Lesson 5: Error Handling Task Statement Learning Goals Code Solution Run the code example Task Statement Learning Goals Code Solution Run the code example Relevant Routines: Lesson 6: Windows, and Cells Programming task Learning Goals Code Solution Run the code example Related Routines Lesson 7: Utility and Constants Routines Task Statement Learning Goals Code Solution Run the code example Task Statement Code Solution Run the code example Related Routines Other Stuff (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. Overview
Note About HTML Links
In order for the links to be resolved, if not done already by installing the lessons package under the Toolkit's ``doc/html'' directory, create a subdirectory called ``lessons'' under the ``doc/html'' directory of the ``cspice/'' tree and copy this document to that subdirectory before loading it into a Web browser. References
Of these documents, the ``Tutorials'' contains the highest level descriptions with the least number of details while the ``Required Reading'' documents contain much more detailed specifications. The most complete specifications are provided in the ``API Documentation''. Tutorials
Name Lesson steps/functions it describes ---------------- ----------------------------------------------- concepts Concepts of space geometry and time intro_to_kernels Using kernels, meta-kernels time Time systems, conversions and formats lsk_and_sclk LSK and SCLK derived_quant "high-level" observation geometry computations other_functions Intro to some SPICE "low level" computations exceptions built-in mechanism for trapping/handling errorsThese tutorials are available from the NAIF server at JPL:
https://naif.jpl.nasa.gov/naif/tutorials.html Required Readings
Name Lesson steps/functions that it describes --------------- ----------------------------------------- cells.req The SPICE cell data type error.req The SPICE error handling system kernel.req Loading SPICE kernels time.req Time conversion windows.req The SPICE window data type The Permuted Index
This text document provides a simple mechanism by which users can discover which CSPICE functions perform functions of interest, as well as the names of the source files that contain these functions. API Documentation
For example the path of the source code of the str2et_c routine is
cspice/src/cspice/str2et_c.c Kernels Used
# FILE NAME TYPE DESCRIPTION -- ------------ ---- ------------------------------------------------ 1 naif0008.tls LSK Generic LSK 2 de405s.bsp SPK Planet Ephemeris SPK 3 pck00008.tpc PCK Generic PCKThese SPICE kernels are included in the lesson package. CSPICE Modules Used
CHAPTER EXERCISE FUNCTIONS NON-VOID KERNELS ------- --------- --------- --------- ---------- 1 kpool furnsh_c 1-3 ktotal_c kdata_c unload_c 2 kervar furnsh_c 1-3 gnpool_c dtpool_c gdpool_c gcpool_c 3 coord furnsh_c dpr_c 1-3 prompt_c str2et_c bodvrd_c spkpos_c recrad_c reclat_c recsph_c recgeo_c 4 xtic furnsh_c jyear_c 1 str2et_c timout_c tpictr_c tsetyr_c 5 errsys chkin_c failed_c erract_c prompt_c chkout_c setmsg_c errdp_c errint_c errch_c sigerr_c aderr erract_c eqstr_c 1-3 furnsh_c failed_c prompt_c spkezr_c reset_c 6 win furnsh_c card_c 1-3 str2et_c size_c wnvald_c wnintd_c wnfetd_c et2utc_c wnsumd_c 7 units prompt_c tkvrsn_c prsdp_c eqstr_c convrt_c xconst spd_c dpr_c rpd_c clight_c j2100_c j2000_c tyear_c halfpi_cRefer to the headers of the various functions listed above, as detailed interface specifications are provided with the source code. NAIF Documentation
Required Reading and Users Guides
abcorr.req cells.req ck.req cspice.req daf.req das.req dla.req dsk.req ek.req ellipses.req error.req frames.req gf.req kernel.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 dskbrief.ug dskexp.ug frmdiff.ug inspekt.ug mkdsk.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
../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 Text kernels
The subsystem uses two tags:
\begintextand
\begindatato 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. Lesson 1: Kernel Management with the Kernel SubsystemTask Statement
Learning Goals
This lesson requires creation of a SPICE meta kernel. Code SolutionFirst, create a meta text kernel:
KPL/MK \begindata KERNELS_TO_LOAD = ( 'kernels/spk/de405s.bsp', 'kernels/pck/pck00008.tpc', 'kernels/lsk/naif0008.tls' ) \begintext... or a more generic meta kernel using the PATH_VALUES/PATH_SYMBOLS functionality to declare path names as variables:
KPL/MK Define the paths to the kernel directory. Use the PATH_SYMBOLS as aliases to the paths. The names and contents of the kernels referenced by this meta-kernel are as follows: File Name Description --------------- ------------------------------ naif0008.tls Generic LSK. de405s.bsp Planet Ephemeris SPK. pck00008.tpc Generic PCK. \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 = "kpool.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: %d\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: %d\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: %d\n", count ); exit(0); } Run the code example
Then 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.
Kernel count after load: 4 File kpool.tm Type META Source File kernels/lsk/naif0008.tls Type TEXT Source kpool.tm File kernels/spk/de405s.bsp Type SPK Source kpool.tm File kernels/pck/pck00008.tpc Type TEXT Source kpool.tm Kernel count after one unload: 3 Kernel count after meta unload: 0 Lesson 2: The Kernel PoolTask Statement
Learning Goals
For the code examples, use this generic text kernel (kervar.tm) containing PCK-type data, kernels to load, and example time strings:
KPL/MK Name the kernels to load. Use path symbols. The names and contents of the kernels referenced by this meta-kernel are as follows: File Name Description --------------- ------------------------------ naif0008.tls Generic LSK. de405s.bsp Planet Ephemeris SPK. pck00008.tpc Generic PCK. \begindata PATH_VALUES = ('kernels/spk', 'kernels/pck', 'kernels/lsk') PATH_SYMBOLS = ('SPK' , 'PCK' , 'LSK' ) KERNELS_TO_LOAD = ( '$SPK/de405s.bsp', '$PCK/pck00008.tpc', '$LSK/naif0008.tls') \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 ) \begintextThe main references for pool routines are found in the source files or API documentation for the particular routines. Code Solution
#include <stdlib.h> #include <stdio.h> #include <string.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 ( "kervar.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( "Number variables matching template: %d\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 ( " Number items: %d 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: %20.6f\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: %20.6f\n", dvars[j] ); } exit(0); } Run the code example
The 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.
Number variables matching template: 6 BODY699_RING1_1 Number 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 Number 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 Number 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_NAME Number items: 1 Of type: C String value: Encke Gap BODY699_RING2_NAME Number items: 1 Of type: C String value: Cassini Division BODY699_RING1_NAME Number items: 1 Of type: C String value: A Ring EXAMPLE_TIMES Time value: 134094896.789000 Time value: 134094896.789000 Time value: 134094896.789753Note 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. Related Routines
Lesson 3: Coordinate ConversionsTask Statement
Learning Goals
This lesson presents these coordinate transform routines for rectangular, cylindrical, and spherical systems. 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 ( "coord.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: %20.6f\n", range ); printf ( " RA : %20.6f\n", ra * dpr_c() ); printf ( " DEC : %20.6f\n", dec* dpr_c() ); /* ...latitudinal coordinates... */ reclat_c ( pos, &range, &lon, &lat ); printf ( " Latitudinal\n" ); printf ( " Rad : %20.6f\n", range); printf ( " Lon : %20.6f\n", lon * dpr_c() ); printf ( " Lat : %20.6f\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 : %20.6f\n", range ); printf ( " Lon : %20.6f\n", lon * dpr_c() ); printf ( " Colat: %20.6f\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 : %20.6f\n", range ); printf ( " Lon : %20.6f\n", lon * dpr_c() ); printf ( " Lat : %20.6f\n", lat * dpr_c() ); /* ...spherical coordinates... */ recsph_c ( pos, &range, &colat, &lon ); printf ( " Spherical\n" ); printf ( " Rad : %20.6f\n", range ); printf ( " Lon : %20.6f\n", lon * dpr_c() ); printf ( " Colat: %20.6f\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 : %20.6f\n", range ); printf ( " Lon : %20.6f\n", lon * dpr_c() ); printf ( " Lat : %20.6f\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: J2000Convert the Moon Cartesian coordinates to right ascension declination.
Range/Ra/Dec Range: 369340.815193 RA : 203.643686 DEC : -4.979010Latitudinal. 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 : -4.979010Spherical. 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: 94.979010The same position look-up in a body fixed (non-inertial) frame, IAU_EARTH.
Non-inertial Frame: IAU_EARTHLatitudinal coordinates return the geocentric latitude.
Latitudinal Rad : 369340.815193 Lon : 70.986950 Lat : -4.989675Spherical.
Spherical Rad : 369340.815193 Lon : 70.986950 Colat: 94.989675Geodetic. The cartographic lat/lon.
Geodetic Rad : 362962.836755 Lon : 70.986950 Lat : -4.990249 Related Routines
Lesson 4: Advanced Time Manipulation RoutinesTask Statement
Learning Goals
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 META variable to the name of the meta-kernel that contains the LSK kernel and create an arbitrary time string. */ SpiceChar * CALSTR = "Mar 15, 2003 12:34:56.789 AM PST"; SpiceChar * META = "xtic.tm"; SpiceChar * AMBIGSTR = "Mar 15, 79 12:34:56"; /* Load the meta-kernel. */ furnsh_c ( META ); 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 : %20.6f\n", et ); /* Make a picture of an output format. Describe a Unix-like time string then send the picture and the 'et' value through 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: %20.6f\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 HandlingTask Statement
Learning Goals
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: N0067 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. D ata added to long error message string: A double 1.8628239700000E+05, an int 66 6, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSC --> DOERR Oh, by the way: The SPICELIB error handling actions are USER-TAILORA BLE. 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 ERRP RT. ===================================================================== ===========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: N0067 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. D ata added to long error message string: A double 1.8628239700000E+05, an int 66 6, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSC --> 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: N0067 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. D ata added to long error message string: A double 1.8628239700000E+05, an int 66 6, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSC --> 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: N0067 OOPS(SOMETHINGBAD) -- A truly horrendous event occurred during execution of this program. D ata added to long error message string: A double 1.8628239700000E+05, an int 66 6, and a string A STRING. A traceback follows. The name of the highest level module is first. ERRSYSC --> DOERR ===================================================================== =========== Error signal noted. Current error state: RETURNThe 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. Task Statement
Learning Goals
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 ( "aderr.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 : %20.6f %20.6f %20.6f\n", state[0] , state[1], state[2] ); printf ( "V : %20.6f %20.6f %20.6f\n", state[3] , state[4], state[5] ); printf ( "LT: %20.6f\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 : -291584.616595 -266693.402359 -76095.647558 V : 0.643439 -0.666066 -0.301310 LT: 1.342311 Target: Mars R : 234536077.419136 -132584383.595569 -63102685.706191 V : 30.961373 28.932996 13.113031 LT: 923.001080 Target: Pluto barycenter R : -1451304742.838526 -4318174144.406321 -918251433.587357 V : 35.079843 3.053138 -0.036762 LT: 15501.258293 Target: Puck ===================================================================== =========== Toolkit version: N0067 SPICE(SPKINSUFFDATA) -- Insufficient ephemeris data has been loaded to compute the state of 7 15 (PUCK) relative to 0 (SOLAR SYSTEM BARYCENTER) at the ephemeris epoch 2000 J AN 01 12:00:00.000. A traceback follows. The name of the highest level module is first. spkezr_c --> SPKEZR --> SPKEZ --> SPKACS --> SPKAPS --> SPKLTC --> SP KGEO ===================================================================== =========== Target: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, this time for "Casper"
Target: Casper ===================================================================== =========== Toolkit version: N0067 SPICE(IDCODENOTFOUND) -- The target, 'Casper', is not a recognized name for an ephemeris objec t. 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 SP ICE ID codes for both 'Casper' and 'EARTH' A traceback follows. The name of the highest level module is first. spkezr_c --> SPKEZR ===================================================================== =========== Target:An easy to understand error. The SPICE system does not contain information on a body named 'Casper.' Another look-up, this time, "Venus".
Target: Venus R : -80970027.540532 -139655772.573898 -53860125.958201 V : 31.166910 -27.001056 -12.316514 LT: 567.655074 Target:The 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. Relevant Routines:
Lesson 6: Windows, and CellsProgramming task
Learning Goals
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 iwhere
a < b i - iThe 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+1A common use of the windows facility is to calculate the intersection set of a number of time intervals. 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 ( "win.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 : %2d\n", (int)card_c(&sched) ); printf( "Space available for values in sched: %2d\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( "%2d %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 : %16.6f\n", meas ); printf( "o Average measure of sched : %16.6f\n", avg ); printf( "o Standard deviation of\n " ); printf( " the measures in sched : %16.6f\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: %2d\n", (int)small/2 ); printf( "o Index of longest interval : %2d\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: 8List 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 02:18:01.000Finally, 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 : 25980.000009 o Average measure of sched : 8660.000003 o Standard deviation of the measures in sched : 5958.550217 o Index of shortest interval: 1 o Index of longest interval : 0 Related Routines
Lesson 7: Utility and Constants RoutinesTask Statement
Learning Goals
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( "\nConvert 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 ( "%12f.6 %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_N0067 From Units : klicks From Value : 3 To Units : miles 1.864114.6 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_N0067 From Units : miles From Value : 26.2 To Units : km 42.164813.6 km Task Statement
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 Related Routines
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