Breaking change: renamed Julian date constants and removed other Julian date constants

src/epoch/mod.rs

@@ -33,8 +33,7 @@ use crate::leap_seconds::{LatestLeapSeconds, LeapSecondProvider};
 use crate::Weekday;
 use crate::{
     EpochError, MonthName, TimeScale, TimeUnits, BDT_REF_EPOCH, ET_EPOCH_S, GPST_REF_EPOCH,
-    GST_REF_EPOCH, J1900_OFFSET, J2000_TO_J1900_DURATION, MJD_OFFSET, NANOSECONDS_PER_DAY,
-    QZSST_REF_EPOCH, UNIX_REF_EPOCH,
+    GST_REF_EPOCH, MJD_J1900, MJD_OFFSET, NANOSECONDS_PER_DAY, QZSST_REF_EPOCH, UNIX_REF_EPOCH,
 };
 use core::cmp::Eq;
 use core::str::FromStr;
@@ -356,7 +355,7 @@ impl Epoch {
             days.is_finite(),
             "Attempted to initialize Epoch with non finite number"
         );
-        Self::from_tai_duration((days - J1900_OFFSET) * Unit::Day)
+        Self::from_tai_duration((days - MJD_J1900) * Unit::Day)
     }
 
     fn from_mjd_in_time_scale(days: f64, time_scale: TimeScale) -> Self {
@@ -396,7 +395,7 @@ impl Epoch {
             days.is_finite(),
             "Attempted to initialize Epoch with non finite number"
         );
-        Self::from_tai_duration((days - J1900_OFFSET - MJD_OFFSET) * Unit::Day)
+        Self::from_tai_duration((days - MJD_J1900 - MJD_OFFSET) * Unit::Day)
     }
 
     fn from_jde_in_time_scale(days: f64, time_scale: TimeScale) -> Self {
@@ -820,7 +819,7 @@ impl Epoch {
     #[must_use]
     /// Returns this epoch as a duration in the requested units in MJD TAI
     pub fn to_mjd_tai(&self, unit: Unit) -> f64 {
-        (self.to_tai_duration() + Unit::Day * J1900_OFFSET).to_unit(unit)
+        (self.to_tai_duration() + Unit::Day * MJD_J1900).to_unit(unit)
     }
 
     #[must_use]
@@ -832,7 +831,7 @@ impl Epoch {
     #[must_use]
     /// Returns the Modified Julian Date in the provided unit in UTC.
     pub fn to_mjd_utc(&self, unit: Unit) -> f64 {
-        (self.to_utc_duration() + Unit::Day * J1900_OFFSET).to_unit(unit)
+        (self.to_utc_duration() + Unit::Day * MJD_J1900).to_unit(unit)
     }
 
     #[must_use]
@@ -858,7 +857,7 @@ impl Epoch {
     #[must_use]
     /// Returns the Julian Days from epoch 01 Jan -4713 12:00 (noon) as a Duration
     pub fn to_jde_tai_duration(&self) -> Duration {
-        self.to_tai_duration() + Unit::Day * J1900_OFFSET + Unit::Day * MJD_OFFSET
+        self.to_tai_duration() + Unit::Day * MJD_J1900 + Unit::Day * MJD_OFFSET
     }
 
     #[must_use]
@@ -876,7 +875,7 @@ impl Epoch {
     #[must_use]
     /// Returns the Julian days in UTC as a `Duration`
     pub fn to_jde_utc_duration(&self) -> Duration {
-        self.to_utc_duration() + Unit::Day * (J1900_OFFSET + MJD_OFFSET)
+        self.to_utc_duration() + Unit::Day * (MJD_J1900 + MJD_OFFSET)
     }
 
     #[must_use]
@@ -923,7 +922,7 @@ impl Epoch {
 
     #[must_use]
     pub fn to_jde_tt_duration(&self) -> Duration {
-        self.to_tt_duration() + Unit::Day * (J1900_OFFSET + MJD_OFFSET)
+        self.to_tt_duration() + Unit::Day * (MJD_J1900 + MJD_OFFSET)
     }
 
     #[must_use]
@@ -934,7 +933,7 @@ impl Epoch {
 
     #[must_use]
     pub fn to_mjd_tt_duration(&self) -> Duration {
-        self.to_tt_duration() + Unit::Day * J1900_OFFSET
+        self.to_tt_duration() + Unit::Day * MJD_J1900
     }
 
     #[must_use]
@@ -1075,13 +1074,6 @@ impl Epoch {
         self.to_et_duration().to_seconds()
     }
 
-    #[must_use]
-    /// Returns the Ephemeris Time in duration past 1900 JAN 01 at noon.
-    /// **Only** use this if the subsequent computation expect J1900 seconds.
-    pub fn to_et_duration_since_j1900(&self) -> Duration {
-        self.to_et_duration() + J2000_TO_J1900_DURATION
-    }
-
     #[must_use]
     /// Returns the duration between J2000 and the current epoch as per NAIF SPICE.
     ///
@@ -1120,13 +1112,6 @@ impl Epoch {
         self.to_tdb_duration().to_seconds()
     }
 
-    #[must_use]
-    /// Returns the Dynamics Barycentric Time (TDB) as a high precision Duration with reference epoch of 1900 JAN 01 at noon.
-    /// **Only** use this if the subsequent computation expect J1900 seconds.
-    pub fn to_tdb_duration_since_j1900(&self) -> Duration {
-        self.to_tdb_duration() + J2000_TO_J1900_DURATION
-    }
-
     #[must_use]
     /// Returns the Ephemeris Time JDE past epoch
     pub fn to_jde_et_days(&self) -> f64 {
@@ -1136,7 +1121,7 @@ impl Epoch {
     #[must_use]
     pub fn to_jde_et_duration(&self) -> Duration {
         self.to_et_duration()
-            + Unit::Day * (J1900_OFFSET + MJD_OFFSET)
+            + Unit::Day * (MJD_J1900 + MJD_OFFSET)
             + TimeScale::ET.prime_epoch_offset()
     }
 
@@ -1148,7 +1133,7 @@ impl Epoch {
     #[must_use]
     pub fn to_jde_tdb_duration(&self) -> Duration {
         self.to_tdb_duration()
-            + Unit::Day * (J1900_OFFSET + MJD_OFFSET)
+            + Unit::Day * (MJD_J1900 + MJD_OFFSET)
             + TimeScale::TDB.prime_epoch_offset()
     }
 

src/lib.rs

@@ -10,25 +10,18 @@
  * Documentation: https://nyxspace.com/
  */
 
-pub const J1900_NAIF: f64 = 2_415_020.0;
-pub const J2000_NAIF: f64 = 2_451_545.0;
-/// `J1900_OFFSET` determines the offset in julian days between 01 Jan 1900 at midnight and the
-/// Modified Julian Day at 17 November 1858.
-/// NOTE: Julian days "start" at noon so that astronomical observations throughout the night
-/// happen at the same Julian day. Note however that the Modified Julian Date (MJD) starts at
-/// midnight, not noon, cf. <http://tycho.usno.navy.mil/mjd.html>.
-pub const J1900_OFFSET: f64 = 15_020.0;
-/// `J2000_OFFSET` determines the offset in julian days between 01 Jan 2000 at **noon** and the
-/// Modified Julian Day at 17 November 1858.
-pub const J2000_OFFSET: f64 = 51_544.5;
+/// Julian date for the J1900 epoch, as per NAIF SPICE.
+pub const JD_J1900: f64 = 2_415_020.0;
+/// Julian date for the J2000 epoch, as per NAIF SPICE.
+pub const JD_J2000: f64 = 2_451_545.0;
+/// Julian days between 01 Jan 1900 at midnight and the Modified Julian Day at 17 November 1858.
+pub const MJD_J1900: f64 = 15_020.0;
+/// Julian days between 01 Jan 2000 at **noon** and the Modified Julian Day at 17 November 1858.
+pub const MJD_J2000: f64 = 51_544.5;
 /// The Ephemeris Time epoch, in seconds
 pub const ET_EPOCH_S: i64 = 3_155_716_800;
 /// Modified Julian Date in seconds as defined [here](http://tycho.usno.navy.mil/mjd.html). MJD epoch is Modified Julian Day at 17 November 1858 at midnight.
 pub const MJD_OFFSET: f64 = 2_400_000.5;
-/// The JDE offset in days
-pub const JDE_OFFSET_DAYS: f64 = J1900_OFFSET + MJD_OFFSET;
-/// The JDE offset in seconds
-pub const JDE_OFFSET_SECONDS: f64 = JDE_OFFSET_DAYS * SECONDS_PER_DAY;
 /// `DAYS_PER_YEAR` corresponds to the number of days per year in the Julian calendar.
 pub const DAYS_PER_YEAR: f64 = 365.25;
 /// `DAYS_PER_YEAR_NLD` corresponds to the number of days per year **without leap days**.
@@ -55,12 +48,6 @@ pub const SECONDS_PER_TROPICAL_YEAR: f64 = 31_556_925.974_7;
 /// `SECONDS_PER_SIDEREAL_YEAR` corresponds to the number of seconds per sidereal year from [NIST](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9#TIME).
 pub const SECONDS_PER_SIDEREAL_YEAR: f64 = 31_558_150.0;
 
-/// The duration between J2000 and J1900 is exactly one century, both references start at noon.
-pub const J2000_TO_J1900_DURATION: Duration = Duration {
-    centuries: 1,
-    nanoseconds: 0,
-};
-
 // Epoch formatting module is called `efmt` to avoid collision with `std::fmt` and `core::fmt`.
 pub mod efmt;
 mod parser;

tests/epoch.rs

@@ -4,9 +4,8 @@ extern crate core;
 use hifitime::{
     is_gregorian_valid, Duration, Epoch, EpochError, ParsingError, TimeScale, TimeUnits, Unit,
     Weekday, BDT_REF_EPOCH, DAYS_GPS_TAI_OFFSET, DAYS_PER_YEAR, GPST_REF_EPOCH, GST_REF_EPOCH,
-    J1900_OFFSET, J1900_REF_EPOCH, J2000_OFFSET, J2000_REF_EPOCH, J2000_TO_J1900_DURATION,
-    MJD_OFFSET, SECONDS_BDT_TAI_OFFSET, SECONDS_GPS_TAI_OFFSET, SECONDS_GST_TAI_OFFSET,
-    SECONDS_PER_DAY,
+    J1900_REF_EPOCH, J2000_REF_EPOCH, JD_J2000, MJD_J1900, MJD_J2000, MJD_OFFSET,
+    SECONDS_BDT_TAI_OFFSET, SECONDS_GPS_TAI_OFFSET, SECONDS_GST_TAI_OFFSET, SECONDS_PER_DAY,
 };
 
 use hifitime::efmt::{Format, Formatter};
@@ -25,15 +24,15 @@ fn test_const_ops() {
     // Tests that multiplying a constant with a unit returns the correct number in that same unit
     let mjd_offset = MJD_OFFSET * Unit::Day;
     assert!((mjd_offset.to_unit(Unit::Day) - MJD_OFFSET).abs() < f64::EPSILON);
-    let j2000_offset = J2000_OFFSET * Unit::Day;
-    assert!((j2000_offset.to_unit(Unit::Day) - J2000_OFFSET).abs() < f64::EPSILON);
+    let j2000_mjd = MJD_J2000 * Unit::Day;
+    assert!((j2000_mjd.to_unit(Unit::Day) - MJD_J2000).abs() < f64::EPSILON);
 }
 
 #[allow(clippy::float_equality_without_abs)]
 #[test]
 fn utc_epochs() {
-    assert!(Epoch::from_mjd_tai(J1900_OFFSET).to_tai_seconds() < EPSILON);
-    assert!((Epoch::from_mjd_tai(J1900_OFFSET).to_mjd_tai_days() - J1900_OFFSET).abs() < EPSILON);
+    assert!(Epoch::from_mjd_tai(MJD_J1900).to_tai_seconds() < EPSILON);
+    assert!((Epoch::from_mjd_tai(MJD_J1900).to_mjd_tai_days() - MJD_J1900).abs() < EPSILON);
 
     // Tests are chronological dates.
     // All of the following examples are cross validated against NASA HEASARC,
@@ -422,11 +421,6 @@ fn gpst() {
         GPST_REF_EPOCH.duration
     );
 
-    // assert_eq!(
-    //     GPST_REF_EPOCH.to_utc_seconds(),
-    //     Epoch::from_gregorian_utc_at_midnight(1980, 1, 6).to_tai_seconds()
-    // );
-
     assert!(
         GPST_REF_EPOCH.to_gpst_seconds().abs() < EPSILON,
         "The number of seconds from the GPS epoch was not 0: {}",
@@ -1918,7 +1912,7 @@ fn test_to_tai_time_scale() {
     let j2000_ref = J2000_REF_EPOCH;
     assert_eq!(j2000_ref, j2000_ref.to_time_scale(TimeScale::TAI));
     let j2000_to_j1900 = j2000_ref - j1900_ref;
-    assert_eq!(j2000_to_j1900, J2000_TO_J1900_DURATION);
+    assert_eq!(j2000_to_j1900, Duration::from_parts(1, 0));
 }
 
 #[cfg(feature = "std")]
@@ -2044,3 +2038,28 @@ fn regression_test_gh_209() {
     let t = Epoch::from_time_of_week(1982, 604800000000000 - 19000000000, TimeScale::GPST);
     println!("{t}");
 }
+
+#[cfg(feature = "std")]
+#[test]
+fn regression_test_gh_282() {
+    assert_eq!(
+        "1900-01-01T00:00:00 UTC",
+        format!("{}", Epoch::from_utc_duration(0_f64.nanoseconds()))
+    );
+    // NOTE: Hifitime's prime epoch is midnight on 1900-01-01, but the Julian date J1900 is at noon.
+    // This explains why the calculation returns `0.5` with a zero duration UTC epoch.
+    assert_eq!(
+        "2415020.5",
+        format!(
+            "{}",
+            Epoch::from_utc_duration(0_f64.nanoseconds()).to_jde_utc_days()
+        )
+    );
+    assert_eq!(
+        "2000-01-01T12:00:00 TAI",
+        format!(
+            "{}",
+            Epoch::from_jde_tai(JD_J2000).to_gregorian_str(hifitime::TimeScale::TAI)
+        )
+    );
+}