Correct handling of navigational status in RMC and GNS (#108)

* Correct handling of navigational status in RMC and GNS

There was a misunderstanding on what the "navigation status" field
should include. The enum values were for the "positioning system mode
indicator" which is the preceding field. This changes the enum values to
correspond to actual ones.

gns.go

@@ -79,13 +79,10 @@ func newGNS(s BaseSentence) (Sentence, error) {
 		m.NavStatus = p.EnumString(
 			12,
 			"navigation status",
-			NavStatusAutonomous,
-			NavStatusDifferential,
-			NavStatusEstimated,
-			NavStatusManualInput,
-			NavStatusSimulated,
-			NavStatusDataNotValid,
-			NavStatusDataValid,
+			NavStatusSafe,
+			NavStatusCaution,
+			NavStatusUnsafe,
+			NavStatusNotValid,
 		)
 	}
 	return m, p.Err()

rmc.go

@@ -58,13 +58,10 @@ func newRMC(s BaseSentence) (Sentence, error) {
 		m.NavStatus = p.EnumString(
 			12,
 			"navigation status",
-			NavStatusAutonomous,
-			NavStatusDifferential,
-			NavStatusEstimated,
-			NavStatusManualInput,
-			NavStatusSimulated,
-			NavStatusDataNotValid,
-			NavStatusDataValid,
+			NavStatusSafe,
+			NavStatusCaution,
+			NavStatusUnsafe,
+			NavStatusNotValid,
 		)
 	}
 	return m, p.Err()

rmc_test.go

@@ -110,14 +110,30 @@ var rmctests = []struct {
 			Date:      Date{Valid: true, DD: 30, MM: 5, YY: 18},
 			Variation: 0,
 			FFAMode:   FAAModeAutonomous,
-			NavStatus: NavStatusDataValid,
+			NavStatus: NavStatusNotValid,
 		},
 	},
 	{
 		name: "bad validity",
 		raw:  "$GPRMC,220516,D,5133.82,N,00042.24,W,173.8,231.8,130694,004.2,W*75",
 		err:  "nmea: GPRMC invalid validity: D",
 	},
+	{
+		name: "good sentence G with nav status",
+		raw:  "$YDRMC,124014.00,A,5520.2848,N,01321.5108,E,0.0,0.0,230623,4.4,E,A,C*5D",
+		msg: RMC{
+			Time:      Time{Valid: true, Hour: 12, Minute: 40, Second: 14, Millisecond: 0},
+			Validity:  "A",
+			Latitude:  55.338080000000005,
+			Longitude: 13.358513333333333,
+			Speed:     0,
+			Course:    0,
+			Date:      Date{Valid: true, DD: 23, MM: 6, YY: 23},
+			Variation: 4.4,
+			FFAMode:   FAAModeAutonomous,
+			NavStatus: NavStatusCaution,
+		},
+	},
 }
 
 func TestRMC(t *testing.T) {

types.go

@@ -127,20 +127,22 @@ const (
 
 // Navigation Status (NMEA 4.1 and later)
 const (
-	// NavStatusAutonomous is Autonomous mode
-	NavStatusAutonomous = "A"
-	// NavStatusDifferential is Differential Mode
-	NavStatusDifferential = "D"
-	// NavStatusEstimated is Estimated (dead-reckoning) mode
-	NavStatusEstimated = "E"
-	// NavStatusManualInput is Manual Input Mode
-	NavStatusManualInput = "M"
-	// NavStatusSimulated is Simulated Mode
+	// NavStatusSimulated is a deprecated placeholder for backwards
+	// compatibility. There is no such status in NMEA.
+	// Deprecated: use NavStatusSafe
 	NavStatusSimulated = "S"
-	// NavStatusDataNotValid is Data Not Valid
-	NavStatusDataNotValid = "N"
-	// NavStatusDataValid is valid
+	// NavStatusDataValid is a deprecated placeholder for backwards
+	// compatibility. There is no such status in NMEA.
+	// Deprecated: use NavStatusNotValid
 	NavStatusDataValid = "V"
+	// NavStatusSafe is Safe (within selected accuracy level)
+	NavStatusSafe = "S"
+	// NavStatusCaution is Caution (integrity not available)
+	NavStatusCaution = "C"
+	// NavStatusUnsafe is Unsafe (outside selected accuracy level)
+	NavStatusUnsafe = "U"
+	// NavStatusNotValid is Not Valid (equipment does not provide navigation status information)
+	NavStatusNotValid = "V"
 )
 
 const (