Base staleness check on TLE Epoch instead of wall clock (#63)

Change quick_predict to use epoch for staleness

Updates the quick_predict function to use the TLE's epoch for checking if the TLE is too stale,
rather than the current system time, allowing for predictions of TLE's older than a year, if
the prediction time is within a year of the TLE's epoch.

Also removes the now unused Daynum2String function and frozen time debug features.

predict.c

@@ -119,14 +119,6 @@
 static PyObject *PredictException;
 static PyObject *NoTransitException;
 
-/*
-  TODO: This is a refactoring hack to ensure we get consistent before/after
-        tests.  Freezes the clock to a specified time, making calculations
-        deterministic. (remove when finished along with (2) call sites)
-*/
-char debug_freeze_time = 0;
-struct tm debug_frozen_tm = { tm_year: 114, tm_mon: 10, tm_mday: 2 };
-
 // This struct represents an observation of a particular satellite
 // from a particular reference point (on earth) at a particular time
 // and is used primarily in the PyPredict code.
@@ -175,8 +167,8 @@ struct	{
  	   long catnum;          // Catalog Number (a.k.a NORAD id)
 	   long setnum;          // Element Set No.
 	   char designator[10];  // Designator
- 	   int year;             // Reference Epoch (year?) (?)
-	   double refepoch;      // Reference Epoch (?)
+	   int year;             // Reference Epoch from TLE (2-digit year)
+	   double refepoch;      // Reference Epoch from TLE (day of the year and fractional portion of the day)
 	   double incl;          // Inclination
 	   double raan;          // RAAN
 	   double eccn;          // Eccentricity
@@ -2083,13 +2075,6 @@ void Calculate_RADec(double time, vector_t *pos, vector_t *vel, geodetic_t *geod
 
 time_t CurrentTime()
 {
-	//TODO: Refactoring Hack (remove)
-	if (debug_freeze_time)
-	{
-		time_t debug_frozen_time = mktime(&debug_frozen_tm);
-		return debug_frozen_time;
-	}
-
 	return time(NULL);
 }
 
@@ -2610,14 +2595,6 @@ double CurrentDaynum()
 {
 	/* Read the system clock and return the number
 	   of days since 31Dec79 00:00:00 UTC (daynum 0) */
-
-	//TODO: Refactoring Hack (remove)
-	if (debug_freeze_time)
-	{
-		time_t debug_frozen_time = mktime(&debug_frozen_tm);
-		return ((((double)debug_frozen_time)/86400.0) - 3651.0);
-	}
-
 	int x;
 	struct timeval tptr;
 	double usecs, seconds;
@@ -2630,44 +2607,6 @@ double CurrentDaynum()
 	return ((seconds/86400.0)-3651.0);
 }
 
-char *Daynum2String(daynum)
-double daynum;
-{
-	/* This function takes the given epoch as a fractional number of
-	   days since 31Dec79 00:00:00 UTC and returns the corresponding
-	   date as a string of the form "Tue 12Oct99 17:22:37". */
-
-	char timestr[26];
-	time_t t;
-	int x;
-
-	/* Convert daynum to Unix time (seconds since 01-Jan-70) */
-	t=(time_t)(86400.0*(daynum+3651.0));
-
-	sprintf(timestr,"%s",asctime(gmtime(&t)));
-
-	if (timestr[8]==' ')
-	{
-		timestr[8]='0';
-	}
-
-	for (x=0; x<=3; output[x]=timestr[x], x++);
-
-	output[4]=timestr[8];
-	output[5]=timestr[9];
-	output[6]=timestr[4];
-	output[7]=timestr[5];
-	output[8]=timestr[6];
-	output[9]=timestr[22];
-	output[10]=timestr[23];
-	output[11]=' ';
-
-	for (x=12; x<=19; output[x]=timestr[x-1], x++);
-
-	output[20]=0;
-	return output;
-}
-
 void FindMoon(double daynum)
 {
 	/* This function determines the position of the moon, including
@@ -3543,7 +3482,7 @@ static char quick_find_docs[] =
 
 static PyObject* quick_predict(PyObject* self, PyObject *args)
 {
-	double now;
+	double tle_epoch;
 	int lastel=0;
 	char errbuff[100];
 	observation obs = { 0 };
@@ -3554,18 +3493,16 @@ static PyObject* quick_predict(PyObject* self, PyObject *args)
 		goto cleanup_and_raise_exception;
 	}
 
-	now=CurrentDaynum();
-
 	if (load(args) != 0)
 	{
 		// load will set the appropriate exception string if it fails.
 		goto cleanup_and_raise_exception;
 	}
 
-	//TODO: Seems like this should be based on the freshness of the TLE, not wall clock.
-	if ((daynum<now-365.0) || (daynum>now+365.0))
+	tle_epoch=(double)DayNum(1,0,sat.year)+sat.refepoch;
+	if ((daynum<tle_epoch-365.0) || (daynum>tle_epoch+365.0))
 	{
-		sprintf(errbuff, "time %s too far from present\n", Daynum2String(daynum));
+		sprintf(errbuff, "day number %.0f too far from tle epoch day %.0f\n", daynum, tle_epoch);
 		PyErr_SetString(PredictException, errbuff);
 		goto cleanup_and_raise_exception;
 	}

setup.py

@@ -7,7 +7,7 @@
 
 setup(
     name="pypredict",
-    version="1.7.1",
+    version="1.7.2",
     author="Jesse Trutna",
     author_email="[email protected]",
     maintainer="Spire Global Inc",

test_predict.py

@@ -1,4 +1,7 @@
 import predict
+import pytest
+
+from cpredict import PredictException
 
 TLE = (
     "0 ISS (ZARYA)\n"
@@ -9,6 +12,9 @@
 T1_IN_TRANSIT = 1680782200  # 2023-04-06T11:56:40Z
 T2_NOT_IN_TRANSIT = 1680783900  # 2023-04-06T12:25:00Z
 
+T1_WITHIN_A_YEAR = 1680782200  # 2023-04-06T11:56:40Z
+T2_AFTER_A_YEAR = 1713897435  # 2024-04-23T18:37:15Z
+
 
 def test_transits_are_truncated_if_the_overlap_the_start_or_end_times():
     tle = predict.massage_tle(TLE)
@@ -24,3 +30,14 @@ def test_transits_are_truncated_if_the_overlap_the_start_or_end_times():
 
     # should not raise a StopIteration
     next(predict.transits(tle, qth, ending_after=at))
+
+
+def test_predict_of_tle_older_than_a_year():
+    # Test a TLE older than a year with a timestamp within a year of its epoch
+    # Should not throw an exception
+    predict.quick_predict(TLE, T1_WITHIN_A_YEAR, QTH)
+
+    # Test a TLE older than a year with a timestamp outwith a year of its epoch
+    # Should raise a PredictException
+    with pytest.raises(PredictException) as e_info:
+        predict.quick_predict(TLE, T2_AFTER_A_YEAR, QTH)