Andy K / Mbed 2 deprecated SOWB

Satellite Observers Workbench. NOT yet complete, just published for forum posters to \"cherry pick\" pieces of code as requiered as an example.

Dependencies:   mbed

sgp4sdp4/sgp_time.c@0:0a841b89d614, 2010-10-11 (annotated)

Committer:
AjK
Date:
Mon Oct 11 10:34:55 2010 +0000
Revision:
0:0a841b89d614
Totally Alpha quality as this project isn\t completed. Just publishing it as it answers many questions asked in the forums

Who changed what in which revision?

UserRevisionLine numberNew contents of line
AjK 0:0a841b89d614 1 /*
AjK 0:0a841b89d614 2 * Unit SGP_Time
AjK 0:0a841b89d614 3 * Author: Dr TS Kelso
AjK 0:0a841b89d614 4 * Original Version: 1992 Jun 02
AjK 0:0a841b89d614 5 * Current Revision: 2000 Jan 22
AjK 0:0a841b89d614 6 * Modified for Y2K: 1999 Mar 07
AjK 0:0a841b89d614 7 * Version: 2.05
AjK 0:0a841b89d614 8 * Copyright: 1992-1999, All Rights Reserved
AjK 0:0a841b89d614 9 * Version 1.50 added Y2K support. Due to limitations in the current
AjK 0:0a841b89d614 10 * format of the NORAD two-line element sets, however, only dates
AjK 0:0a841b89d614 11 * through 2056 December 31/2359 UTC are valid.
AjK 0:0a841b89d614 12 * Version 1.60 modifies Calendar_Date to ensure date matches time
AjK 0:0a841b89d614 13 * resolution and modifies Time_of_Day to make it more robust.
AjK 0:0a841b89d614 14 * Version 2.00 adds Julian_Date, Date_Time, and Check_Date to support
AjK 0:0a841b89d614 15 * checking for valid date/times, permitting the use of Time_to_UTC and
AjK 0:0a841b89d614 16 * Time_from_UTC for UTC/local time conversions.
AjK 0:0a841b89d614 17 * Version 2.05 modifies UTC_offset to allow non-integer offsets.
AjK 0:0a841b89d614 18 *
AjK 0:0a841b89d614 19 * Ported to C by: Neoklis Kyriazis April 9 2001
AjK 0:0a841b89d614 20 */
AjK 0:0a841b89d614 21
AjK 0:0a841b89d614 22 #include "sgp4sdp4.h"
AjK 0:0a841b89d614 23
AjK 0:0a841b89d614 24 /* The function Julian_Date_of_Epoch returns the Julian Date of */
AjK 0:0a841b89d614 25 /* an epoch specified in the format used in the NORAD two-line */
AjK 0:0a841b89d614 26 /* element sets. It has been modified to support dates beyond */
AjK 0:0a841b89d614 27 /* the year 1999 assuming that two-digit years in the range 00-56 */
AjK 0:0a841b89d614 28 /* correspond to 2000-2056. Until the two-line element set format */
AjK 0:0a841b89d614 29 /* is changed, it is only valid for dates through 2056 December 31. */
AjK 0:0a841b89d614 30
AjK 0:0a841b89d614 31 double
AjK 0:0a841b89d614 32 Julian_Date_of_Epoch(double epoch)
AjK 0:0a841b89d614 33 {
AjK 0:0a841b89d614 34 double year,day;
AjK 0:0a841b89d614 35
AjK 0:0a841b89d614 36 /* Modification to support Y2K */
AjK 0:0a841b89d614 37 /* Valid 1957 through 2056 */
AjK 0:0a841b89d614 38 day = modf(epoch*1E-3, &year)*1E3;
AjK 0:0a841b89d614 39 if( year < 57 )
AjK 0:0a841b89d614 40 year = year + 2000;
AjK 0:0a841b89d614 41 else
AjK 0:0a841b89d614 42 year = year + 1900;
AjK 0:0a841b89d614 43 /* End modification */
AjK 0:0a841b89d614 44
AjK 0:0a841b89d614 45 return( Julian_Date_of_Year(year) + day );
AjK 0:0a841b89d614 46 } /*Function Julian_Date_of_Epoch*/
AjK 0:0a841b89d614 47
AjK 0:0a841b89d614 48 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 49
AjK 0:0a841b89d614 50 /* Converts a Julian epoch to NORAD TLE epoch format */
AjK 0:0a841b89d614 51 double
AjK 0:0a841b89d614 52 Epoch_Time(double jd)
AjK 0:0a841b89d614 53 {
AjK 0:0a841b89d614 54 double yr,_time,epoch_time;
AjK 0:0a841b89d614 55 struct tm edate;
AjK 0:0a841b89d614 56
AjK 0:0a841b89d614 57 Calendar_Date(jd, &edate);
AjK 0:0a841b89d614 58 yr = edate.tm_year - 100*(edate.tm_year/100) ;
AjK 0:0a841b89d614 59 _time = Frac(jd + 0.5);
AjK 0:0a841b89d614 60 epoch_time = yr*1000
AjK 0:0a841b89d614 61 + DOY(edate.tm_year, edate.tm_mon, edate.tm_mday)
AjK 0:0a841b89d614 62 + _time;
AjK 0:0a841b89d614 63
AjK 0:0a841b89d614 64 return( epoch_time );
AjK 0:0a841b89d614 65 } /*Function Epoch_Time*/
AjK 0:0a841b89d614 66
AjK 0:0a841b89d614 67 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 68
AjK 0:0a841b89d614 69 /* The function DOY calculates the day of the year for the specified */
AjK 0:0a841b89d614 70 /* date. The calculation uses the rules for the Gregorian calendar */
AjK 0:0a841b89d614 71 /* and is valid from the inception of that calendar system. */
AjK 0:0a841b89d614 72 int
AjK 0:0a841b89d614 73 DOY(int yr, int mo, int dy)
AjK 0:0a841b89d614 74 {
AjK 0:0a841b89d614 75 const int days[] = {31,28,31,30,31,30,31,31,30,31,30,31};
AjK 0:0a841b89d614 76 int i,day;
AjK 0:0a841b89d614 77
AjK 0:0a841b89d614 78 day = 0;
AjK 0:0a841b89d614 79 for( i = 0; i < mo-1; i++ )
AjK 0:0a841b89d614 80 day += days[i];
AjK 0:0a841b89d614 81 day = day + dy;
AjK 0:0a841b89d614 82
AjK 0:0a841b89d614 83 /* Leap year correction */
AjK 0:0a841b89d614 84 if(
AjK 0:0a841b89d614 85 (yr%4 == 0) && ((yr%100 != 0) || (yr%400 == 0)) && (mo>2)
AjK 0:0a841b89d614 86 )
AjK 0:0a841b89d614 87 day++;
AjK 0:0a841b89d614 88
AjK 0:0a841b89d614 89 return( day );
AjK 0:0a841b89d614 90 } /*Function DOY*/
AjK 0:0a841b89d614 91
AjK 0:0a841b89d614 92 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 93
AjK 0:0a841b89d614 94 /* Fraction_of_Day calculates the fraction of */
AjK 0:0a841b89d614 95 /* a day passed at the specified input time. */
AjK 0:0a841b89d614 96 double
AjK 0:0a841b89d614 97 Fraction_of_Day(int hr,int mi,int se)
AjK 0:0a841b89d614 98 {
AjK 0:0a841b89d614 99 return( (hr + (mi + se/60.0)/60.0)/24.0 );
AjK 0:0a841b89d614 100 } /*Function Fraction_of_Day*/
AjK 0:0a841b89d614 101
AjK 0:0a841b89d614 102 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 103
AjK 0:0a841b89d614 104 /* The function Calendar_Date converts a Julian Date to a struct tm. */
AjK 0:0a841b89d614 105 /* Only the members tm_year, tm_mon and tm_mday are calculated and set */
AjK 0:0a841b89d614 106 void
AjK 0:0a841b89d614 107 Calendar_Date(double jd, struct tm *cdate)
AjK 0:0a841b89d614 108 {
AjK 0:0a841b89d614 109 /* Astronomical Formulae for Calculators, Jean Meeus, pages 26-27 */
AjK 0:0a841b89d614 110 int Z,month;
AjK 0:0a841b89d614 111 double A,B,C,D,E,F,alpha,day,year,factor;
AjK 0:0a841b89d614 112
AjK 0:0a841b89d614 113 factor = 0.5/secday/1000;
AjK 0:0a841b89d614 114 F = Frac(jd + 0.5);
AjK 0:0a841b89d614 115 if (F + factor >= 1.0)
AjK 0:0a841b89d614 116 {
AjK 0:0a841b89d614 117 jd = jd + factor;
AjK 0:0a841b89d614 118 F = 0.0;
AjK 0:0a841b89d614 119 } /*if*/
AjK 0:0a841b89d614 120 Z = Round(jd);
AjK 0:0a841b89d614 121 if( Z < 2299161 )
AjK 0:0a841b89d614 122 A = Z;
AjK 0:0a841b89d614 123 else
AjK 0:0a841b89d614 124 {
AjK 0:0a841b89d614 125 alpha = Int((Z - 1867216.25)/36524.25);
AjK 0:0a841b89d614 126 A = Z + 1 + alpha - Int(alpha/4);
AjK 0:0a841b89d614 127 } /*else*/
AjK 0:0a841b89d614 128 B = A + 1524;
AjK 0:0a841b89d614 129 C = Int((B - 122.1)/365.25);
AjK 0:0a841b89d614 130 D = Int(365.25 * C);
AjK 0:0a841b89d614 131 E = Int((B - D)/30.6001);
AjK 0:0a841b89d614 132 day = B - D - Int(30.6001 * E) + F;
AjK 0:0a841b89d614 133
AjK 0:0a841b89d614 134 if( E < 13.5 )
AjK 0:0a841b89d614 135 month = Round(E - 1);
AjK 0:0a841b89d614 136 else
AjK 0:0a841b89d614 137 month = Round(E - 13);
AjK 0:0a841b89d614 138 if( month > 2.5 )
AjK 0:0a841b89d614 139 year = C - 4716;
AjK 0:0a841b89d614 140 else
AjK 0:0a841b89d614 141 year = C - 4715;
AjK 0:0a841b89d614 142
AjK 0:0a841b89d614 143 cdate->tm_year = (int) year;
AjK 0:0a841b89d614 144 cdate->tm_mon = month;
AjK 0:0a841b89d614 145 cdate->tm_mday = (int) floor(day);
AjK 0:0a841b89d614 146
AjK 0:0a841b89d614 147 } /*Function Calendar_Date*/
AjK 0:0a841b89d614 148
AjK 0:0a841b89d614 149 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 150
AjK 0:0a841b89d614 151 /* Time_of_Day takes a Julian Date and calculates the clock time */
AjK 0:0a841b89d614 152 /* portion of that date. Only tm_hour, tm_min and tm_sec are set */
AjK 0:0a841b89d614 153 void
AjK 0:0a841b89d614 154 Time_of_Day(double jd, struct tm *cdate)
AjK 0:0a841b89d614 155 {
AjK 0:0a841b89d614 156 int hr,mn,sc;
AjK 0:0a841b89d614 157 double _time;
AjK 0:0a841b89d614 158
AjK 0:0a841b89d614 159 _time = Frac(jd - 0.5)*secday;
AjK 0:0a841b89d614 160 _time = Round(_time);
AjK 0:0a841b89d614 161 hr = floor(_time/3600.0);
AjK 0:0a841b89d614 162 _time = _time - 3600.0*hr;
AjK 0:0a841b89d614 163 if( hr == 24 ) hr = 0;
AjK 0:0a841b89d614 164 mn = floor(_time/60.0);
AjK 0:0a841b89d614 165 sc = _time - 60.0*mn;
AjK 0:0a841b89d614 166 cdate->tm_hour = hr;
AjK 0:0a841b89d614 167 cdate->tm_min = mn;
AjK 0:0a841b89d614 168 cdate->tm_sec = sc;
AjK 0:0a841b89d614 169
AjK 0:0a841b89d614 170 } /*Function Time_of_Day*/
AjK 0:0a841b89d614 171
AjK 0:0a841b89d614 172 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 173
AjK 0:0a841b89d614 174 /* The function Julian_Date converts a standard calendar */
AjK 0:0a841b89d614 175 /* date and time to a Julian Date. The procedure Date_Time */
AjK 0:0a841b89d614 176 /* performs the inverse of this function. */
AjK 0:0a841b89d614 177 double
AjK 0:0a841b89d614 178 Julian_Date(struct tm *cdate)
AjK 0:0a841b89d614 179 {
AjK 0:0a841b89d614 180 double julian_date;
AjK 0:0a841b89d614 181
AjK 0:0a841b89d614 182 julian_date = Julian_Date_of_Year(cdate->tm_year) +
AjK 0:0a841b89d614 183 DOY(cdate->tm_year,cdate->tm_mon,cdate->tm_mday) +
AjK 0:0a841b89d614 184 Fraction_of_Day(cdate->tm_hour,cdate->tm_min,cdate->tm_sec);
AjK 0:0a841b89d614 185
AjK 0:0a841b89d614 186 return( julian_date );
AjK 0:0a841b89d614 187 } /*Function Julian_Date */
AjK 0:0a841b89d614 188
AjK 0:0a841b89d614 189 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 190
AjK 0:0a841b89d614 191
AjK 0:0a841b89d614 192 /* Date_Time()
AjK 0:0a841b89d614 193 *
AjK 0:0a841b89d614 194 * The function Date_Time() converts a Julian Date to
AjK 0:0a841b89d614 195 * standard calendar date and time. The function
AjK 0:0a841b89d614 196 * Julian_Date() performs the inverse of this function.
AjK 0:0a841b89d614 197 */
AjK 0:0a841b89d614 198
AjK 0:0a841b89d614 199 void
AjK 0:0a841b89d614 200 Date_Time(double julian_date, struct tm *cdate)
AjK 0:0a841b89d614 201 {
AjK 0:0a841b89d614 202 time_t jtime;
AjK 0:0a841b89d614 203
AjK 0:0a841b89d614 204 jtime = (julian_date - 2440587.5)*86400.;
AjK 0:0a841b89d614 205 *cdate = *gmtime( &jtime );
AjK 0:0a841b89d614 206
AjK 0:0a841b89d614 207 } /* End of Date_Time() */
AjK 0:0a841b89d614 208
AjK 0:0a841b89d614 209
AjK 0:0a841b89d614 210 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 211
AjK 0:0a841b89d614 212 /* The procedure Check_Date can be used as a check to see if a calendar */
AjK 0:0a841b89d614 213 /* date and time are valid. It works by first converting the calendar */
AjK 0:0a841b89d614 214 /* date and time to a Julian Date (which allows for irregularities, such */
AjK 0:0a841b89d614 215 /* as a time greater than 24 hours) and then converting back and comparing.*/
AjK 0:0a841b89d614 216 int
AjK 0:0a841b89d614 217 Check_Date(struct tm *cdate)
AjK 0:0a841b89d614 218 {
AjK 0:0a841b89d614 219 double jt;
AjK 0:0a841b89d614 220 struct tm chkdate;
AjK 0:0a841b89d614 221
AjK 0:0a841b89d614 222 jt = Julian_Date(cdate);
AjK 0:0a841b89d614 223 Date_Time(jt, &chkdate);
AjK 0:0a841b89d614 224
AjK 0:0a841b89d614 225 if( (cdate->tm_year == chkdate.tm_year) &&
AjK 0:0a841b89d614 226 (cdate->tm_mon == chkdate.tm_mon ) &&
AjK 0:0a841b89d614 227 (cdate->tm_mday == chkdate.tm_mday) &&
AjK 0:0a841b89d614 228 (cdate->tm_hour == chkdate.tm_hour) &&
AjK 0:0a841b89d614 229 (cdate->tm_min == chkdate.tm_min ) &&
AjK 0:0a841b89d614 230 (cdate->tm_sec == chkdate.tm_sec ) )
AjK 0:0a841b89d614 231 return ( 1 );
AjK 0:0a841b89d614 232 else
AjK 0:0a841b89d614 233 return( 0 );
AjK 0:0a841b89d614 234
AjK 0:0a841b89d614 235 } /*Procedure Check_Date*/
AjK 0:0a841b89d614 236
AjK 0:0a841b89d614 237 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 238
AjK 0:0a841b89d614 239 /* Procedures Time_to_UTC and Time_from_UTC are used to */
AjK 0:0a841b89d614 240 /* convert 'struct tm' dates between UTC and local time. */
AjK 0:0a841b89d614 241 /* The procedures JD_to_UTC and JD_from_UTC are used to */
AjK 0:0a841b89d614 242 /* do the same thing working directly with Julian dates. */
AjK 0:0a841b89d614 243
AjK 0:0a841b89d614 244 struct tm
AjK 0:0a841b89d614 245 Time_to_UTC(struct tm *cdate)
AjK 0:0a841b89d614 246 {
AjK 0:0a841b89d614 247 time_t tdate;
AjK 0:0a841b89d614 248
AjK 0:0a841b89d614 249 tdate = mktime(cdate);
AjK 0:0a841b89d614 250 return( *gmtime(&tdate) );
AjK 0:0a841b89d614 251 } /*Procedure Time_to_UTC*/
AjK 0:0a841b89d614 252
AjK 0:0a841b89d614 253 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 254
AjK 0:0a841b89d614 255 struct tm
AjK 0:0a841b89d614 256 Time_from_UTC(struct tm *cdate)
AjK 0:0a841b89d614 257 {
AjK 0:0a841b89d614 258 time_t tdate;
AjK 0:0a841b89d614 259
AjK 0:0a841b89d614 260 tdate = mktime(cdate);
AjK 0:0a841b89d614 261 return( *localtime(&tdate) );
AjK 0:0a841b89d614 262 } /*Procedure Time_from_UTC*/
AjK 0:0a841b89d614 263
AjK 0:0a841b89d614 264 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 265
AjK 0:0a841b89d614 266 /*
AjK 0:0a841b89d614 267 BSD systems don't define the timezone variable, so the following two
AjK 0:0a841b89d614 268 routines won't work. They're not used anyway in the example main(),
AjK 0:0a841b89d614 269 so we might as well comment them out.
AjK 0:0a841b89d614 270 */
AjK 0:0a841b89d614 271
AjK 0:0a841b89d614 272 #if 0
AjK 0:0a841b89d614 273
AjK 0:0a841b89d614 274 double
AjK 0:0a841b89d614 275 JD_to_UTC(double jt)
AjK 0:0a841b89d614 276 {
AjK 0:0a841b89d614 277 extern long timezone;
AjK 0:0a841b89d614 278 struct tm cdate;
AjK 0:0a841b89d614 279
AjK 0:0a841b89d614 280 time_t t = 0;
AjK 0:0a841b89d614 281
AjK 0:0a841b89d614 282 cdate = *localtime( &t );
AjK 0:0a841b89d614 283 jt = jt - timezone/secday;
AjK 0:0a841b89d614 284 if( cdate.tm_isdst )
AjK 0:0a841b89d614 285 jt= jt - 1.0/24.0;
AjK 0:0a841b89d614 286
AjK 0:0a841b89d614 287 return( jt );
AjK 0:0a841b89d614 288 } /*Procedure JD_to_UTC*/
AjK 0:0a841b89d614 289
AjK 0:0a841b89d614 290 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 291
AjK 0:0a841b89d614 292 double
AjK 0:0a841b89d614 293 JD_from_UTC(double jt)
AjK 0:0a841b89d614 294 {
AjK 0:0a841b89d614 295 extern long timezone;
AjK 0:0a841b89d614 296 struct tm cdate;
AjK 0:0a841b89d614 297 time_t t = 0;
AjK 0:0a841b89d614 298
AjK 0:0a841b89d614 299 cdate = *localtime( &t );
AjK 0:0a841b89d614 300 jt = jt + timezone/secday;
AjK 0:0a841b89d614 301 if( cdate.tm_isdst )
AjK 0:0a841b89d614 302 jt= jt + 1.0/24.0;
AjK 0:0a841b89d614 303
AjK 0:0a841b89d614 304 return( jt );
AjK 0:0a841b89d614 305 } /*Procedure JD_from_UTC*/
AjK 0:0a841b89d614 306
AjK 0:0a841b89d614 307 #endif
AjK 0:0a841b89d614 308
AjK 0:0a841b89d614 309 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 310
AjK 0:0a841b89d614 311 /* The function Delta_ET has been added to allow calculations on */
AjK 0:0a841b89d614 312 /* the position of the sun. It provides the difference between UT */
AjK 0:0a841b89d614 313 /* (approximately the same as UTC) and ET (now referred to as TDT).*/
AjK 0:0a841b89d614 314 /* This function is based on a least squares fit of data from 1950 */
AjK 0:0a841b89d614 315 /* to 1991 and will need to be updated periodically. */
AjK 0:0a841b89d614 316
AjK 0:0a841b89d614 317 double
AjK 0:0a841b89d614 318 Delta_ET(double year)
AjK 0:0a841b89d614 319 {
AjK 0:0a841b89d614 320 /* Values determined using data from 1950-1991 in the 1990
AjK 0:0a841b89d614 321 Astronomical Almanac. See DELTA_ET.WQ1 for details. */
AjK 0:0a841b89d614 322
AjK 0:0a841b89d614 323 double delta_et;
AjK 0:0a841b89d614 324
AjK 0:0a841b89d614 325 delta_et = 26.465 + 0.747622*(year - 1950) +
AjK 0:0a841b89d614 326 1.886913*sin(twopi*(year - 1975)/33);
AjK 0:0a841b89d614 327
AjK 0:0a841b89d614 328 return( delta_et );
AjK 0:0a841b89d614 329 } /*Function Delta_ET*/
AjK 0:0a841b89d614 330
AjK 0:0a841b89d614 331 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 332
AjK 0:0a841b89d614 333 /* The function Julian_Date_of_Year calculates the Julian Date */
AjK 0:0a841b89d614 334 /* of Day 0.0 of {year}. This function is used to calculate the */
AjK 0:0a841b89d614 335 /* Julian Date of any date by using Julian_Date_of_Year, DOY, */
AjK 0:0a841b89d614 336 /* and Fraction_of_Day. */
AjK 0:0a841b89d614 337
AjK 0:0a841b89d614 338 double
AjK 0:0a841b89d614 339 Julian_Date_of_Year(double year)
AjK 0:0a841b89d614 340 {
AjK 0:0a841b89d614 341 /* Astronomical Formulae for Calculators, Jean Meeus, */
AjK 0:0a841b89d614 342 /* pages 23-25. Calculate Julian Date of 0.0 Jan year */
AjK 0:0a841b89d614 343
AjK 0:0a841b89d614 344 long A,B,i;
AjK 0:0a841b89d614 345 double jdoy;
AjK 0:0a841b89d614 346
AjK 0:0a841b89d614 347 year = year-1;
AjK 0:0a841b89d614 348 i = year/100;
AjK 0:0a841b89d614 349 A = i;
AjK 0:0a841b89d614 350 i = A/4;
AjK 0:0a841b89d614 351 B = 2-A+i;
AjK 0:0a841b89d614 352 i = 365.25*year;
AjK 0:0a841b89d614 353 i += 30.6001*14;
AjK 0:0a841b89d614 354 jdoy = i+1720994.5+B;
AjK 0:0a841b89d614 355
AjK 0:0a841b89d614 356 return (jdoy);
AjK 0:0a841b89d614 357 } /*Function Julian_Date_of_Year*/
AjK 0:0a841b89d614 358
AjK 0:0a841b89d614 359 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 360
AjK 0:0a841b89d614 361 /* The function ThetaG calculates the Greenwich Mean Sidereal Time */
AjK 0:0a841b89d614 362 /* for an epoch specified in the format used in the NORAD two-line */
AjK 0:0a841b89d614 363 /* element sets. It has now been adapted for dates beyond the year */
AjK 0:0a841b89d614 364 /* 1999, as described above. The function ThetaG_JD provides the */
AjK 0:0a841b89d614 365 /* same calculation except that it is based on an input in the */
AjK 0:0a841b89d614 366 /* form of a Julian Date. */
AjK 0:0a841b89d614 367
AjK 0:0a841b89d614 368 double
AjK 0:0a841b89d614 369 ThetaG(double epoch, deep_arg_t *deep_arg)
AjK 0:0a841b89d614 370 {
AjK 0:0a841b89d614 371 /* Reference: The 1992 Astronomical Almanac, page B6. */
AjK 0:0a841b89d614 372
AjK 0:0a841b89d614 373 double year,day,UT,jd,TU,GMST,_ThetaG;
AjK 0:0a841b89d614 374
AjK 0:0a841b89d614 375 /* Modification to support Y2K */
AjK 0:0a841b89d614 376 /* Valid 1957 through 2056 */
AjK 0:0a841b89d614 377 day = modf(epoch*1E-3,&year)*1E3;
AjK 0:0a841b89d614 378 if(year < 57)
AjK 0:0a841b89d614 379 year += 2000;
AjK 0:0a841b89d614 380 else
AjK 0:0a841b89d614 381 year += 1900;
AjK 0:0a841b89d614 382 /* End modification */
AjK 0:0a841b89d614 383
AjK 0:0a841b89d614 384 UT = modf(day,&day);
AjK 0:0a841b89d614 385 jd = Julian_Date_of_Year(year)+day;
AjK 0:0a841b89d614 386 TU = (jd-2451545.0)/36525;
AjK 0:0a841b89d614 387 GMST = 24110.54841+TU*(8640184.812866+TU*(0.093104-TU* 6.2E-6));
AjK 0:0a841b89d614 388 GMST = Modulus(GMST+secday*omega_E*UT,secday);
AjK 0:0a841b89d614 389 _ThetaG = twopi*GMST/secday;
AjK 0:0a841b89d614 390 deep_arg->ds50 = jd-2433281.5+UT;
AjK 0:0a841b89d614 391 _ThetaG = FMod2p(6.3003880987*deep_arg->ds50+1.72944494);
AjK 0:0a841b89d614 392
AjK 0:0a841b89d614 393 return (_ThetaG);
AjK 0:0a841b89d614 394 } /* Function ThetaG */
AjK 0:0a841b89d614 395
AjK 0:0a841b89d614 396 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 397
AjK 0:0a841b89d614 398 double
AjK 0:0a841b89d614 399 ThetaG_JD(double jd)
AjK 0:0a841b89d614 400 {
AjK 0:0a841b89d614 401 /* Reference: The 1992 Astronomical Almanac, page B6. */
AjK 0:0a841b89d614 402
AjK 0:0a841b89d614 403 double UT,TU,GMST;
AjK 0:0a841b89d614 404
AjK 0:0a841b89d614 405 UT = Frac(jd + 0.5);
AjK 0:0a841b89d614 406 jd = jd - UT;
AjK 0:0a841b89d614 407 TU = (jd - 2451545.0)/36525;
AjK 0:0a841b89d614 408 GMST = 24110.54841 + TU * (8640184.812866 + TU * (0.093104 - TU * 6.2E-6));
AjK 0:0a841b89d614 409 GMST = Modulus(GMST + secday*omega_E*UT,secday);
AjK 0:0a841b89d614 410
AjK 0:0a841b89d614 411 return( twopi * GMST/secday );
AjK 0:0a841b89d614 412 } /*Function ThetaG_JD*/
AjK 0:0a841b89d614 413
AjK 0:0a841b89d614 414 /*------------------------------------------------------------------*/
AjK 0:0a841b89d614 415
AjK 0:0a841b89d614 416 /* Gets calendar time from time() and produces a UTC calendar date */
AjK 0:0a841b89d614 417 void
AjK 0:0a841b89d614 418 UTC_Calendar_Now( struct tm *cdate )
AjK 0:0a841b89d614 419 {
AjK 0:0a841b89d614 420 time_t t;
AjK 0:0a841b89d614 421
AjK 0:0a841b89d614 422 t = time(0);
AjK 0:0a841b89d614 423 *cdate = *gmtime(&t);
AjK 0:0a841b89d614 424 cdate->tm_year += 1900;
AjK 0:0a841b89d614 425 cdate->tm_mon += 1;
AjK 0:0a841b89d614 426
AjK 0:0a841b89d614 427 } /* End UTC_Calendar_Now */
AjK 0:0a841b89d614 428 /*------------------------------------------------------------------*/