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Software/Python/grove_gps/dextergps.py

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+# Released under the MIT license (http://choosealicense.com/licenses/mit/).
+# For more information see https://github.com/DexterInd/GrovePi/blob/master/LICENSE
+
+import grovepi
+import serial, time, sys
+import re
+
+en_debug = False
+
+def debug(in_str):
+    if en_debug:
+        print(in_str)
+
+patterns=["$GPGGA",
+    "/[0-9]{6}\.[0-9]{2}/", # timestamp hhmmss.ss
+    "/[0-9]{4}.[0-9]{2,/}", # latitude of position
+    "/[NS]",  # North or South
+    "/[0-9]{4}.[0-9]{2}", # longitude of position
+    "/[EW]",  # East or West
+    "/[012]", # GPS Quality Indicator
+    "/[0-9]+", # Number of satellites
+    "/./", # horizontal dilution of precision x.x
+    "/[0-9]+\.[0-9]*/" # altitude x.x
+    ]
+
+class GROVEGPS():
+    def __init__(self, port='/dev/ttyAMA0', baud=9600, timeout=0):
+        self.ser = serial.Serial(port, baud, timeout=timeout)
+        self.ser.flush()
+        self.raw_line = ""
+        self.gga = []
+        self.validation =[] # contains compiled regex
+
+        # compile regex once to use later
+        for i in range(len(patterns)-1):
+            self.validation.append(re.compile(patterns[i]))
+
+        self.clean_data()
+        # self.get_date()  # attempt to gete date from GPS.
+
+    def clean_data(self):
+        '''
+        clean_data:
+        ensures that all relevant GPS data is set to either empty string
+        or -1.0, or -1, depending on appropriate type
+        This occurs right after initialisation or
+        after 50 attemps to reach GPS
+        '''
+        self.timestamp = ""
+        self.lat = -1.0    # degrees minutes and decimals of minute
+        self.NS = ""
+        self.lon = -1.0
+        self.EW = ""
+        self.quality = -1
+        self.satellites = -1
+        self.altitude = -1.0
+
+        self.latitude = -1.0  #degrees and decimals
+        self.longitude = -1.0
+        self.fancylat = ""  #
+
+    # def get_date(self):
+    #     '''
+    #     attempt to get date from GPS data. So far no luck. GPS does
+    #     not seem to send date sentence at all
+    #     function is unfinished
+    #     '''
+    #     valid = False
+    #     for i in range(50):
+    #         time.sleep(0.5)
+    #         self.raw_line = self.ser.readline().strip()
+    #         if self.raw_line[:6] == "GPZDA":  # found date line!
+    #             print (self.raw_line)
+
+
+    def read(self):
+        '''
+        Attempts 50 times at most to get valid data from GPS
+        Returns as soon as valid data is found
+        If valid data is not found, then clean up data in GPS instance
+        '''
+        valid = False
+        for _ in range(50):
+            time.sleep(0.5)
+            self.raw_line = self.ser.readline()
+            try:
+                self.line = self.raw_line.decode('utf-8')
+                self.line = self.line.strip()
+            except:
+                self.line = ""
+            debug(self.line)
+            if self.validate(self.line):
+                valid = True
+                break
+
+        if valid:
+            return self.gga
+        else:
+            self.clean_data()
+            return []
+
+    def validate(self, in_line):
+        '''
+        Runs regex validation on a GPGAA sentence.
+        Returns False if the sentence is mangled
+        Return True if everything is all right and sets internal
+        class members.
+        '''
+        if in_line == "":
+            return False
+        if in_line[:6] != "$GPGGA":
+            return False
+
+        self.gga = in_line.split(",")
+        debug (self.gga)
+
+        #Sometimes multiple GPS data packets come into the stream. Take the data only after the last '$GPGGA' is seen
+        try:
+            ind=self.gga.index('$GPGGA', 5, len(self.gga))
+            self.gga=self.gga[ind:]
+        except ValueError:
+            pass
+
+        if len(self.gga) != 15:
+            debug ("Failed: wrong number of parameters ")
+            debug (self.gga)
+            return False
+
+        for i in range(len(self.validation)-1):
+            if len(self.gga[i]) == 0:
+                debug ("Failed: empty string %d"%i)
+                return False
+            test = self.validation[i].match(self.gga[i])
+            if test == False:
+                debug ("Failed: wrong format on parameter %d"%i)
+                return False
+            else:
+                debug("Passed %d"%i)
+
+        try:
+            self.timestamp = self.gga[1]
+            self.lat = float(self.gga[2])
+            self.NS = self.gga[3]
+            self.lon = float(self.gga[4])
+            self.EW = self.gga[5]
+            self.quality = int(self.gga[6])
+            self.satellites = int(self.gga[7])
+            self.altitude = float(self.gga[9])
+
+            self.latitude = self.lat // 100 + self.lat % 100 / 60
+            if self.NS == "S":
+                self.latitude = - self.latitude
+            self.longitude = self.lon // 100 + self.lon % 100 / 60
+            if self.EW == "W":
+                self.longitude = -self.longitude
+        except ValueError:
+            debug( "FAILED: invalid value")
+
+        return True
+
+
+if __name__ =="__main__":
+    gps = GROVEGPS()
+    while True:
+        time.sleep(1)
+        in_data = gps.read()
+        if in_data != []:
+            print (in_data)