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micropyGPS/micropyGPS.py

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# MicropyGPS - a GPS NMEA sentence parser for Micropython/Python 3.X
#
# The MIT License (MIT)
# Copyright (c) 2014 Michael Calvin McCoy (calvin.mccoy@gmail.com)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
# documentation files (the “Software”), to deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit
# persons to whom the Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
# Software.
#
# THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
# OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
# TODO:
# Time Since First Fix
# Time Since Last Good Fix
# Statistics
# Sentence size bound checking
class MicropyGPS(object):
"""GPS NMEA Sentence Parser. Creates object that stores all relevant GPS data and statistics.
Parses sentences one character at a time using update(). """
# Max Number of Characters a valid sentence can be (based on GGA sentence)
SENTENCE_LIMIT = 76
def __init__(self, local_offset=0):
"""Setup GPS Object Status Flags, Internal Data Registers, etc"""
#####################
# Object Status Flags
self.sentence_active = False
self.active_segment = 0
self.process_crc = False
self.gps_segments = []
self.crc_xor = 0
self.char_count = 0
#####################
# Data From Sentences
# Time
self.timestamp = (0, 0, 0)
self.date = (0, 0, 0)
self.local_offset = local_offset
# Position/Motion
self.latitude = (0, 0.0, 'N')
self.longitude = (0, 0.0, 'W')
self.speed = (0.0, 0.0, 0.0)
self.course = 0.0
self.altitude = 0.0
self.geoid_height = 0.0
# GPS Info
self.satellites_in_view = 0
self.satellites_in_use = 0
self.satellites_used = []
self.last_sv_sentence = 0
self.total_sv_sentences = 0
self.satellite_data = dict()
self.hdop = 0.0
self.pdop = 0.0
self.vdop = 0.0
self.valid = False
self.fix_stat = 0
self.fix_type = 1
# Object Constants
self.__hemispheres = ('N', 'S', 'E', 'W')
def gprmc(self):
"""Parse Recommended Minimum Specific GPS/Transit data (RMC)Sentence. Updates UTC timestamp, latitude,
longitude, Course, Speed, and Date"""
# UTC Timestamp
try:
utc_string = self.gps_segments[1]
# Skip timestamp if receiver doesn't have one yet
if utc_string:
hours = int(utc_string[0:2]) + self.local_offset
minutes = int(utc_string[2:4])
seconds = float(utc_string[4:])
self.timestamp = (hours, minutes, seconds)
except ValueError:
return False
# Check Receiver Data Valid Flag
if self.gps_segments[2] == 'A': # Data from Receiver is valid
# Longitude / Latitude
try:
# Latitude
l_string = self.gps_segments[3]
lat_degs = int(l_string[0:2])
lat_mins = float(l_string[2:])
lat_hemi = self.gps_segments[4]
# Longitude
l_string = self.gps_segments[5]
lon_degs = int(l_string[0:3])
lon_mins = float(l_string[3:])
lon_hemi = self.gps_segments[6]
except ValueError:
return False
if lat_hemi not in self.__hemispheres:
return False
if lon_hemi not in self.__hemispheres:
return False
# Speed
try:
spd_knt = float(self.gps_segments[7])
except ValueError:
return False
# Date
try:
# NOTE!!! Date string is assumed to be year >=2000,
# Sentences recorded in 90s will display as 209X!!!
# FIXME if you want to parse old GPS logs or are time traveler
date_string = self.gps_segments[9]
day = date_string[0:2]
month = date_string[2:4]
year = date_string[4:6]
except ValueError:
return False
# Course
try:
course = self.gps_segments[8]
except ValueError:
return False
# TODO - Add Magnetic Variation
# Update Object Data
self.latitude = (lat_degs, lat_mins, lat_hemi)
self.longitude = (lon_degs, lon_mins, lon_hemi)
# Include mph and hm/h
self.speed = (spd_knt, spd_knt * 1.151, spd_knt * 1.852)
self.date = (day, month, year)
self.course = course
self.valid = True
else:
return False
return True
def gpvtg(self):
"""Parse Track Made Good and Ground Speed (VTG) Sentence. Updates speed and course"""
try:
course = self.gps_segments[1]
spd_knt = float(self.gps_segments[5])
except ValueError:
return False
# Include mph and hm/h
self.speed = (spd_knt, spd_knt * 1.151, spd_knt * 1.852)
self.course = course
return True
def gpgga(self):
"""Parse Global Positioning System Fix Data (GGA) Sentence. Updates UTC timestamp, latitude, longitude,
fix status, satellites in use, Horizontal Dilution of Precision (HDOP), altitude, and geoid height"""
try:
# UTC Timestamp
utc_string = self.gps_segments[1]
# Skip timestamp if receiver doesn't have on yet
if utc_string:
hours = int(utc_string[0:2]) + self.local_offset
minutes = int(utc_string[2:4])
seconds = float(utc_string[4:])
else:
hours = 0
minutes = 0
seconds = 0.0
# Number of Satellites in Use
satellites_in_use = int(self.gps_segments[7])
# Horizontal Dilution of Precision
hdop = float(self.gps_segments[8])
# Get Fix Status
fix_stat = int(self.gps_segments[6])
except ValueError:
return False
# Process Location and Speed Data if Fix is GOOD
if fix_stat:
# Longitude / Latitude
try:
# Latitude
l_string = self.gps_segments[2]
lat_degs = int(l_string[0:2])
lat_mins = float(l_string[2:])
lat_hemi = self.gps_segments[3]
# Longitude
l_string = self.gps_segments[4]
lon_degs = int(l_string[0:3])
lon_mins = float(l_string[3:])
lon_hemi = self.gps_segments[5]
except ValueError:
return False
if lat_hemi not in self.__hemispheres:
return False
if lon_hemi not in self.__hemispheres:
return False
# Altitude / Height Above Geoid
try:
altitude = float(self.gps_segments[9])
geoid_height = float(self.gps_segments[11])
except ValueError:
return False
# Update Object Data
self.latitude = (lat_degs, lat_mins, lat_hemi)
self.longitude = (lon_degs, lon_mins, lon_hemi)
self.altitude = altitude
self.geoid_height = geoid_height
# Update Object Data
self.timestamp = (hours, minutes, seconds)
self.satellites_in_use = satellites_in_use
self.hdop = hdop
self.fix_stat = fix_stat
return True
def gpgsa(self):
"""Parse GNSS DOP and Active Satellites (GSA) sentence. Updates GPS fix type, list of satellites used in
fix calculation, Position Dilution of Precision (PDOP), Horizontal Dilution of Precision (HDOP), and Vertical
Dilution of Precision"""
# Fix Type (None,2D or 3D)
try:
fix_type = int(self.gps_segments[2])
except ValueError:
return False
# Read All (up to 12) Available PRN Satellite Numbers
sats_used = []
for sats in range(12):
sat_number_str = self.gps_segments[3 + sats]
if sat_number_str:
try:
sat_number = int(sat_number_str)
sats_used.append(sat_number)
except ValueError:
return False
else:
break
# PDOP,HDOP,VDOP
try:
pdop = float(self.gps_segments[15])
hdop = float(self.gps_segments[16])
vdop = float(self.gps_segments[17])
except ValueError:
return False
# Update Object Data
self.fix_type = fix_type
self.satellites_used = sats_used
self.hdop = hdop
self.vdop = vdop
self.pdop = pdop
return True
def gpgsv(self):
"""Parse Satellites in View (GSV) sentence. Updates number of SV Sentences,the number of the last SV sentence
parsed"""
try:
number_of_sv_sentences = int(self.gps_segments[1])
current_sv_sentence = int(self.gps_segments[2])
satellites_in_view = int(self.gps_segments[3])
except ValueError:
return False
# Create a blank dict to store all the satellite data from this sentence in:
# satellite PRN is key, tuple containing telemetry is value
satellite_dict = dict()
# Try to recover data for up to 4 satellites in sentence
for sats in range(4, 20, 4):
# If a PRN is present, grab satellite data
if self.gps_segments[sats]:
try:
sat_id = int(self.gps_segments[sats])
elevation = int(self.gps_segments[sats+1])
azimuth = int(self.gps_segments[sats+2])
except ValueError:
return False
try: # SNR can be null (no value) when not tracking
snr = int(self.gps_segments[sats+3])
except ValueError:
snr = None
# If no PRN is found, then the sentence has no more satellites to read
else:
break
# Add Satellite Data to Sentence Dict
satellite_dict[sat_id] = (elevation, azimuth, snr)
# Update Object Data
self.total_sv_sentences = number_of_sv_sentences
self.last_sv_sentence = current_sv_sentence
self.satellites_in_view = satellites_in_view
# For a new set of sentences, we either clear out the existing sat data or
# update it as additional SV sentences are parsed
if current_sv_sentence == 1:
self.satellite_data = satellite_dict
else:
self.satellite_data.update(satellite_dict)
return True
def new_sentence(self):
"""Adjust Object Flags in Preparation for a New Sentence"""
self.gps_segments = ['']
self.active_segment = 0
self.crc_xor = 0
self.sentence_active = True
self.process_crc = True
self.char_count = 0
def update(self, new_char):
"""Process a new input char and updates GPS object if necessary based on special characters ('$', ',', '*')
Function builds a list of received string that are validate by CRC prior to parsing by the appropriate
sentence function. Returns sentence type on successful parse, None otherwise"""
valid_sentence = False
# Validate new_char is a printable char
ascii_char = ord(new_char)
if 33 <= ascii_char <= 126:
self.char_count += 1
# Check if a new string is starting ($)
if new_char == '$':
self.new_sentence()
return None
elif self.sentence_active:
# Check if sentence is ending (*)
if new_char == '*':
self.process_crc = False
self.active_segment += 1
self.gps_segments.append('')
return None
# Check if a section is ended (,), Create a new substring to feed
# characters to
elif new_char == ',':
self.active_segment += 1
self.gps_segments.append('')
# Store All Other printable character and check CRC when ready
else:
self.gps_segments[self.active_segment] += new_char
# When CRC input is disabled, sentence is nearly complete
if not self.process_crc:
if len(self.gps_segments[self.active_segment]) == 2:
try:
final_crc = int(self.gps_segments[self.active_segment], 16)
if self.crc_xor == final_crc:
valid_sentence = True
except ValueError:
pass # CRC Value was deformed and could not have been correct
# Update CRC
if self.process_crc:
self.crc_xor ^= ascii_char
# If a Valid Sentence Was received and it's a supported sentence, then parse it!!
if valid_sentence :
# Clear Active Processing Flag
self.sentence_active = False
if self.gps_segments[0] in self.supported_sentences:
# parse the Sentence Based on the message type, return True if parse is clean
if self.supported_sentences[self.gps_segments[0]](self):
# Let host know that the GPS object was updated by returning parsed sentence type
return self.gps_segments[0]
# Check that the sentence buffer isn't filling up with Garage waiting for the sentence to complete
if self.char_count > self.SENTENCE_LIMIT:
self.sentence_active = False
# Tell Host no new sentence was parsed
return None
#########################################
# User Helper Functions
# These functions make working with the GPS object data easier
#########################################
def satellite_data_updated(self):
"""
Checks if the all the GSV sentences in a group have been read, making satellite data complete
:return: boolean
"""
if self.total_sv_sentences > 0 and self.total_sv_sentences == self.last_sv_sentence:
return True
else:
return False
def satellites_visible(self):
"""
Returns a list of of the satellite PRNs currently visible to the receiver
:return: list
"""
return list(self.satellite_data.keys())
# All the currently supported NMEA sentences
supported_sentences = {'GPRMC': gprmc, 'GPGGA': gpgga, 'GPVTG': gpvtg, 'GPGSA': gpgsa, 'GPGSV': gpgsv}
if __name__ == "__main__":
test_RMC = ['$GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62',
'$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A',
'$GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E*68',
'$GPRMC,180041.896,A,3749.1851,N,08338.7891,W,001.9,154.9,240911,,,A*7A',
'$GPRMC,180049.896,A,3749.1808,N,08338.7869,W,001.8,156.3,240911,,,A*70',
'$GPRMC,092751.000,A,5321.6802,N,00630.3371,W,0.06,31.66,280511,,,A*45']
test_VTG = ['$GPVTG,232.9,T,,M,002.3,N,004.3,K,A*01']
test_GGA = ['$GPGGA,180050.896,3749.1802,N,08338.7865,W,1,07,1.1,397.4,M,-32.5,M,,0000*6C']
test_GSA = ['$GPGSA,A,3,07,11,28,24,26,08,17,,,,,,2.0,1.1,1.7*37',
'$GPGSA,A,3,07,02,26,27,09,04,15,,,,,,1.8,1.0,1.5*33']
test_GSV = ['$GPGSV,3,1,12,28,72,355,39,01,52,063,33,17,51,272,44,08,46,184,38*74',
'$GPGSV,3,2,12,24,42,058,33,11,34,053,33,07,20,171,40,20,15,116,*71',
'$GPGSV,3,3,12,04,12,204,34,27,11,324,35,32,11,089,,26,10,264,40*7B',
'$GPGSV,3,1,11,03,03,111,00,04,15,270,00,06,01,010,00,13,06,292,00*74',
'$GPGSV,3,2,11,14,25,170,00,16,57,208,39,18,67,296,40,19,40,246,00*74',
'$GPGSV,3,3,11,22,42,067,42,24,14,311,43,27,05,244,00,,,,*4D']
my_gps = MicropyGPS()
sentence = ''
for RMC_sentence in test_RMC:
for y in RMC_sentence:
sentence = my_gps.update(y)
print('Parsed a', sentence, 'Sentence')
print('Parsed Strings:', my_gps.gps_segments)
print('Sentence CRC Value:', hex(my_gps.crc_xor))
print('Longitude:', my_gps.longitude)
print('Latitude', my_gps.latitude)
print('UTC Timestamp:', my_gps.timestamp)
print('Speed:', my_gps.speed)
print('Date Stamp:', my_gps.date)
print('Course', my_gps.course)
print('Data is Valid', my_gps.valid)
print('')
for VTG_sentence in test_VTG:
for y in VTG_sentence:
sentence = my_gps.update(y)
print('Parsed a', sentence, 'Sentence')
print('Parsed Strings', my_gps.gps_segments)
print('Sentence CRC Value:', hex(my_gps.crc_xor))
print('Speed:', my_gps.speed)
print('Course', my_gps.course)
print('')
for GGA_sentence in test_GGA:
for y in GGA_sentence:
sentence = my_gps.update(y)
print('Parsed a', sentence, 'Sentence')
print('Parsed Strings', my_gps.gps_segments)
print('Sentence CRC Value:', hex(my_gps.crc_xor))
print('Longitude', my_gps.longitude)
print('Latitude', my_gps.latitude)
print('UTC Timestamp:', my_gps.timestamp)
print('Fix Status:', my_gps.fix_stat)
print('Altitude:', my_gps.altitude)
print('Height Above Geoid:', my_gps.geoid_height)
print('Horizontal Dilution of Precision:', my_gps.hdop)
print('Satellites in Use by Receiver:', my_gps.satellites_in_use)
print('')
for GSA_sentence in test_GSA:
for y in GSA_sentence:
sentence = my_gps.update(y)
print('Parsed a', sentence, 'Sentence')
print('Parsed Strings', my_gps.gps_segments)
print('Sentence CRC Value:', hex(my_gps.crc_xor))
print('Satellites Used', my_gps.satellites_used)
print('Fix Type Code:', my_gps.fix_type)
print('Horizontal Dilution of Precision:', my_gps.hdop)
print('Vertical Dilution of Precision:', my_gps.vdop)
print('Position Dilution of Precision:', my_gps.pdop)
print('')
for GSV_sentence in test_GSV:
for y in GSV_sentence:
sentence = my_gps.update(y)
print('Parsed a', sentence, 'Sentence')
print('Parsed Strings', my_gps.gps_segments)
print('Sentence CRC Value:', hex(my_gps.crc_xor))
print('SV Sentences Parsed', my_gps.last_sv_sentence)
print('SV Sentences in Total', my_gps.total_sv_sentences)
print('# of Satellites in View:', my_gps.satellites_in_view)
data_valid = my_gps.satellite_data_updated()
print('Is Satellite Data Valid?:', data_valid)
if data_valid:
print('Satellite Data:', my_gps.satellite_data)
print('Satellites Visible:', my_gps.satellites_visible())
print('')
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