Fix BeiDou time

Author: umeat

rtcm3/time.go

@@ -13,6 +13,7 @@ func DF004(e uint32) time.Time {
 }
 
 func DF004Time(e uint32, start time.Time) time.Time {
+	// TODO: GpsLeapSeconds should take a time to return leap seconds as at that time
 	start = start.Add(rtcm.GpsLeapSeconds()) // UTC to GPS time
 	sow := start.Truncate(time.Hour*24).AddDate(0, 0, -int(start.Weekday()))
 	tow := time.Duration(e) * time.Millisecond
@@ -21,10 +22,10 @@ func DF004Time(e uint32, start time.Time) time.Time {
 
 // BeiDou Epoch Time (TOW)
 func DF427(e uint32, start time.Time) time.Time {
-	start = start.Add(rtcm.GpsLeapSeconds()) // UTC to GPS time
-	sow := start.Truncate(time.Hour*24).AddDate(0, 0, -int(start.Weekday())).Add(-14 * time.Second)
+	start = start.Add(rtcm.GpsLeapSeconds() - 14*time.Second) // UTC to GPS time
+	sow := start.Truncate(time.Hour*24).AddDate(0, 0, -int(start.Weekday()))
 	tow := time.Duration(e) * time.Millisecond
-	return sow.Add(-(rtcm.GpsLeapSeconds())).Add(tow)
+	return sow.Add(-(rtcm.GpsLeapSeconds())).Add(tow + 14*time.Second)
 }
 
 // GPS Epoch Time 1s

rtcm3/time_test.go

@@ -20,6 +20,23 @@ func TestDF034(t *testing.T) {
 	}
 }
 
+func TestDF427(t *testing.T) {
+	refTimeG0 := time.Date(2023, 2, 25, 23, 59, 42, 0, time.UTC)
+	if time := rtcm3.DF427(604786000, refTimeG0); time != refTimeG0 {
+		t.Errorf("DF427 time incorrect at GPS 0: %v, expected %v", time, refTimeG0)
+	}
+
+	refTimeB0 := time.Date(2023, 2, 25, 23, 59, 56, 0, time.UTC)
+	if time := rtcm3.DF427(0, refTimeB0); time != refTimeB0 {
+		t.Errorf("DF427 time incorrect at BeiDou 0: %v, expected %v", time, refTimeB0)
+	}
+
+	refTimeX := time.Date(2019, 2, 8, 00, 44, 44, 0, time.UTC)
+	if time := rtcm3.DF034(13484000, refTimeX); time != refTimeX {
+		t.Errorf("DF427 time incorrect: %v, expected %v", time, refTimeX)
+	}
+}
+
 func TestGlonassTimeMSM(t *testing.T) {
 	midweek := time.Date(2019, 3, 28, 4, 2, 9, 0, time.UTC)
 	if time := rtcm3.GlonassTimeMSM(562199912, midweek); time != midweek {