Merge pull request #80 from gamblor21/precision

Add handling with extra precision in lat/long

adafruit_gps.py

@@ -80,10 +80,15 @@ def _parse_degrees(nmea_data):
     # Where ddd is the degrees, mm.mmmm is the minutes.
     if nmea_data is None or len(nmea_data) < 3:
         return None
-    raw = float(nmea_data)
-    deg = raw // 100
-    minutes = raw % 100
-    return deg + minutes / 60
+    # To avoid losing precision handle degrees and minutes separately
+    # Return the final value as an integer. Further functions can parse
+    # this into a float or separate parts to retain the precision
+    raw = nmea_data.split(".")
+    degrees = int(raw[0]) // 100 * 1000000  # the ddd
+    minutes = int(raw[0]) % 100  # the mm.
+    minutes += int(f"{raw[1][:4]:0<4}") / 10000
+    minutes = int(minutes / 60 * 1000000)
+    return degrees + minutes  # return parsed string in the format dddmmmmmm
 
 
 def _parse_int(nmea_data):
@@ -105,12 +110,21 @@ def _parse_str(nmea_data):
 
 
 def _read_degrees(data, index, neg):
-    x = data[index]
+    # This function loses precision with float32
+    x = data[index] / 1000000
     if data[index + 1].lower() == neg:
         x *= -1.0
     return x
 
 
+def _read_int_degrees(data, index, neg):
+    deg = data[index] // 1000000
+    minutes = data[index] % 1000000 / 10000
+    if data[index + 1].lower() == neg:
+        deg *= -1
+    return (deg, minutes)
+
+
 def _parse_talker(data_type):
     # Split the data_type into talker and sentence_type
     if data_type[:1] == b"P":  # Proprietary codes
@@ -208,7 +222,11 @@ def __init__(self, uart, debug=False):
         # Initialize null starting values for GPS attributes.
         self.timestamp_utc = None
         self.latitude = None
+        self.latitude_degrees = None
+        self.latitude_minutes = None  # Use for full precision minutes
         self.longitude = None
+        self.longitude_degrees = None
+        self.longitude_minutes = None  # Use for full precision minutes
         self.fix_quality = 0
         self.fix_quality_3d = 0
         self.satellites = None
@@ -424,9 +442,11 @@ def _parse_gll(self, data):
 
         # Latitude
         self.latitude = _read_degrees(data, 0, "s")
+        self.latitude_degrees, self.latitude_minutes = _read_int_degrees(data, 0, "s")
 
         # Longitude
         self.longitude = _read_degrees(data, 2, "w")
+        self.longitude_degrees, self.longitude_minutes = _read_int_degrees(data, 2, "w")
 
         # UTC time of position
         self._update_timestamp_utc(data[4])
@@ -462,9 +482,11 @@ def _parse_rmc(self, data):
 
         # Latitude
         self.latitude = _read_degrees(data, 2, "s")
+        self.latitude_degrees, self.latitude_minutes = _read_int_degrees(data, 2, "s")
 
         # Longitude
         self.longitude = _read_degrees(data, 4, "w")
+        self.longitude_degrees, self.longitude_minutes = _read_int_degrees(data, 4, "w")
 
         # Speed over ground, knots
         self.speed_knots = data[6]
@@ -498,9 +520,11 @@ def _parse_gga(self, data):
 
         # Latitude
         self.latitude = _read_degrees(data, 1, "s")
+        self.latitude_degrees, self.latitude_minutes = _read_int_degrees(data, 1, "s")
 
         # Longitude
         self.longitude = _read_degrees(data, 3, "w")
+        self.longitude_degrees, self.longitude_minutes = _read_int_degrees(data, 3, "w")
 
         # GPS quality indicator
         # 0 - fix not available,

examples/gps_simpletest.py

@@ -82,6 +82,16 @@
         )
         print("Latitude: {0:.6f} degrees".format(gps.latitude))
         print("Longitude: {0:.6f} degrees".format(gps.longitude))
+        print(
+            "Precise Latitude: {:2.}{:2.4f} degrees".format(
+                gps.latitude_degrees, gps.latitude_minutes
+            )
+        )
+        print(
+            "Precise Longitude: {:2.}{:2.4f} degrees".format(
+                gps.longitude_degrees, gps.longitude_minutes
+            )
+        )
         print("Fix quality: {}".format(gps.fix_quality))
         # Some attributes beyond latitude, longitude and timestamp are optional
         # and might not be present.  Check if they're None before trying to use!

tests/adafruit_gps_test.py

@@ -21,9 +21,9 @@
 @pytest.mark.parametrize(
     ("val", "exp"),
     (
-        pytest.param("0023.456", 0.390933, id="leading zero"),
-        pytest.param("6413.9369", 64.23228, id="regular value"),
-        pytest.param("2747.416122087989", 27.79027, id="long value"),
+        pytest.param("0023.456", 390933, id="leading zero"),
+        pytest.param("6413.9369", 64232281, id="regular value"),
+        pytest.param("2747.416122087989", 27790268, id="long value"),
     ),
 )
 def test_parse_degrees(val, exp):
@@ -61,10 +61,10 @@ def test_parse_float_invalid(val):
 @pytest.mark.parametrize(
     ("data", "neg", "exp"),
     (
-        pytest.param([27.79027, "S"], "s", -27.79027, id="south negative"),
-        pytest.param([64.23228, "N"], "s", 64.23228, id="north not negative"),
-        pytest.param([123.4567, "W"], "w", -123.4567, id="west negative"),
-        pytest.param([10.7891, "E"], "w", 10.7891, id="east not negative"),
+        pytest.param([27790270, "S"], "s", -27.79027, id="south negative"),
+        pytest.param([64232280, "N"], "s", 64.23228, id="north not negative"),
+        pytest.param([123456700, "W"], "w", -123.4567, id="west negative"),
+        pytest.param([10789100, "E"], "w", 10.7891, id="east not negative"),
     ),
 )
 def test_read_degrees(data, neg, exp):