Class: SerialGPS

Inherits:
Object
  • Object
show all
Defined in:
lib/serialgps.rb

Overview

Connects to the GPS unit and parses the NMEA sentences.

Instance Method Summary collapse

Constructor Details

#initialize(device, baud = 4800, bits = 8, stop = 1, parity = SerialPort::NONE) ⇒ SerialGPS

Connect to the serial device.



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# File 'lib/serialgps.rb', line 29

def initialize(device, baud=4800, bits=8, stop=1, parity=SerialPort::NONE)
	@serial = SerialPort.new(device, baud, bits, stop, parity)
	@serial.read_timeout = 30 * 1000 # 10 second timeout for reads
	@data = {}
	@collected = []
end

Instance Method Details

#close ⇒ Object

Close the serial connection to the GPS unit.



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# File 'lib/serialgps.rb', line 37

def close
	@serial.close	
end

#date_time ⇒ Object

Returns a DateTime object representing the date and time provided by the GPS unit or NIL if this data is not available yet.



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# File 'lib/serialgps.rb', line 226

def date_time()
	@data.inspect
	if !@data.key?(:time) || @data[:time].empty? || !@data.key?(:date) || @data[:date].empty?
		return nil
	end

	time = @data[:time]
	date = @data[:date]
	time.gsub!(/\.[0-9]*$/, "") # remove decimals
	datetime = "#{date} #{time} UTC"

	date =  DateTime.strptime(datetime, "%d%m%y %H%M%S %Z")
	date
end

#get_data ⇒ Object

Reads NMEA until at least the GGA and RMC data has been loaded

last_nmea

The last NMEA sentence name (without “$GP”) parsed with the read method.

quality:: 0 = invalid, 1 = GPS fix, 2 = DGPS fix validity:: A = ok, V = invalid latitude:: Latitude lat_ref:: North/South (N/S) longitude:: Longitude long_ref:: East/West (E/W) altitude:: Current altitude alt_unit:: Altitude height unit of measure (i.e. M = Meters) speed:: Speed over ground in knots heading:: Heading, in degrees course:: Course over ground in degrees time:: Current time formated as HHMMSS.SS – use date_time to get the parsed version date:: Current date formated as DDMMYY – use date_time to get the parsed version local_hour_offset:: Local zone description, 00 to +/- 13 hours local_minute_offset:: Local zone minutes description (same sign as hours) num_sat:: The number of satellites in view satellites:: An array with id, elevation, azimuth and SNR for each satellite height_geoid:: Height of geoid above WGS84 ellipsoid height_geoid_unit:: Unit of measure (i.e. M = Meters) last_dgps:: Time since last DGPS update dgps:: DGPS reference station id mode:: M = Manual (forced to operate in 2D or 3D) A = Automatic (3D/2D) mode_dimension:: 1 = Fix not available, 2 = 2D, 3 = 3D hdop:: Horizontal Dilution of Precision pdop:: Positional Dilution of Precision vdop:: Vertical Dilution of Precision msg_count:: Total number of messages of this type in this cycle msg_num:: Message number variation:: Magnetic variation var_direction:: Magnetic variation direction (i.e E = East)



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# File 'lib/serialgps.rb', line 75

def get_data
	data = {}

	reads = 0
	errors = 0
	while true do
		
		begin
			read()
		
			# Have we gathered enough data yet
			if @collected.include?("GGA") && @collected.include?("RMC") && reads > 5
				break
			elsif reads > 25
				raise "Could not gather enough data from the GPS. Perhaps the NMEA data is corrupt. Did you specifiy the correct serial device?"
			end
			
			reads += 1
			errors = 0
		rescue
			errors += 1
			if errors > 5
				raise $!
			end
		end
		
	end

	return @data
end

#live_gps_dump ⇒ Object

Prints the live GPS data to the console.



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# File 'lib/serialgps.rb', line 162

def live_gps_dump
	puts "Reading...\n"
	buffer = ""
	data = {}
	rows = 1
	errors = 0

	while true do
		begin
			read

			# Clear previous data
			if rows > 0
				$stdout.print "\e[#{rows}A\e[E\e[J"
				rows = 0
			end
			errors = 0
			
			# Get date
			date = self.date_time 
			unless date.nil?
				date = date.strftime("%b %d %I:%M %p")
			end
			
			num_sat = data[:num_sat] || 0
			$stdout.print "Time: #{date}		Satellites: #{num_sat}		Quality:#{data[:quality]}\n"
			$stdout.print "Latitude: #{data[:latitude]}#{data[:lat_ref]}"
			$stdout.print "\tLongitude: #{data[:longitude]}#{data[:long_ref]}"
			$stdout.print "\tElevation: #{data[:altitude]}#{data[:alt_unit]}\n"
			rows += 3
			
			# Satellites
			if data.key?(:num_sat)
				$stdout.print "-- Satellites --\n"
				data[:num_sat].times do | i | 
					
					if data[:num_sat][:satellites].size > i
						sat = data[:num_sat][:satellites][i]
						rows += 1
						
						$stdout.print "#{sat[:id]}: "
						$stdout.print "Elevation: #{sat[:elevation]}"
						$stdout.print "\tAzimuth: #{sat[:azimuth]}\n"
					end
				end
				rows += 1
			end
		
		rescue Exception => e
			# Clear previous error
			if errors > 0
				$stdout.print "\e[1A\e[E\e[J"
				errors = 0
			end

			$stdout.print "\nERROR: #{e.message}\n"
			break
		end
		
		$stdout.flush
	end
end

#next_sentence ⇒ Object

Retuns the next raw NMEA sentence string



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# File 'lib/serialgps.rb', line 129

def next_sentence

	# Loop through serial data
	buffer = ""
	while true do
		c = @serial.getc
		if c.nil?
			raise "Can't connection to the GPS!"
		end

		# End of the line, collect the data
		if c == 10
			buffer.lstrip!
			
			# Valid sentence
			if buffer[0,1] == "$"
				break
				
			# Try again, probably a partial line
			else
				buffer = ""
			end
			
		# Add to buffer
		else
			buffer << c
		end
	end
	
	buffer
end

#parse_NMEA(raw) ⇒ Object

Parse a raw NMEA sentence and respond with the data in a hash



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# File 'lib/serialgps.rb', line 242

def parse_NMEA(raw)
	data = { :last_nmea => nil }
	if raw.nil?
		return data
	end
	raw.gsub!(/[\n\r]/, "")

	line = raw.split(",");
	if line.size < 1
		return data
	end
	
	# Invalid sentence, does not begin with '$'
	if line[0][0, 1] != "$"
		return data
	end
	
	# Parse sentence
	type = line[0][3, 3]
	line.shift

	if type.nil?
		return data
	end
	
	case type
		when "GGA"
			data[:last_nmea] = type
			data[:time]					= line.shift
			data[:latitude]			= line.shift
			data[:lat_ref]			= line.shift
			data[:longitude]		= line.shift
			data[:long_ref]			= line.shift
			data[:quality]			= line.shift
			data[:num_sat]			= line.shift.to_i
			data[:hdop]				= line.shift
			data[:altitude]			= line.shift
			data[:alt_unit]			= line.shift
			data[:height_geoid]		= line.shift
			data[:height_geoid_unit] = line.shift
			data[:last_dgps]		= line.shift
			data[:dgps]				= line.shift

		when "RMC"
			data[:last_nmea] = type
			data[:time]			= line.shift
			data[:validity]		= line.shift
			data[:latitude]		= line.shift
			data[:lat_ref]		= line.shift
			data[:longitude]	= line.shift
			data[:long_ref]		= line.shift
			data[:speed]		= line.shift
			data[:course]		= line.shift
			data[:date]			= line.shift
			data[:variation]	= line.shift
			data[:var_direction] = line.shift
			
		when "GLL"
			data[:last_nmea] 	= type
			data[:latitude]		= line.shift
			data[:lat_ref]		= line.shift
			data[:longitude]	= line.shift
			data[:long_ref]		= line.shift
	  	data[:time]				= line.shift
			
		when "RMA"
			data[:last_nmea] = type
			line.shift # data status
			data[:latitude]		= line.shift
			data[:lat_ref]		= line.shift
			data[:longitude]	= line.shift
			data[:long_ref]		= line.shift
	  		line.shift # not used
	  		line.shift # not used
			data[:speed]			= line.shift
			data[:course]			= line.shift
			data[:variation]	= line.shift
			data[:var_direction]	= line.shift
	  	
		when "GSA"
			data[:last_nmea] = type
			data[:mode]						= line.shift
			data[:mode_dimension]	= line.shift
	  	
	  	# Satellite data
	  	data[:satellites] ||= []
	  	12.times do |i|
	  		id = line.shift
	  		
	  		# No satallite ID, clear data for this index
	  		if id.empty?
	  			data[:satellites][i] = {}
	  		
	  		# Add satallite ID
	  		else
		  		data[:satellites][i] ||= {}
		  		data[:satellites][i][:id] = id
	  		end
	  	end
	  	
	  	data[:pdop]			= line.shift
	  	data[:hdop]			= line.shift
	  	data[:vdop]			= line.shift
	  	
		when "GSV"
			data[:last_nmea] 	= type
			data[:msg_count]	= line.shift
			data[:msg_num]		= line.shift
			data[:num_sat]		= line.shift.to_i
			
			# Satellite data
	  		data[:satellites] ||= []
			4.times do |i|
	  			data[:satellites][i] ||= {}
	  		
				data[:satellites][i][:elevation]	= line.shift
				data[:satellites][i][:azimuth]		= line.shift
				data[:satellites][i][:snr]			= line.shift
			end
	  	
	  when "HDT"
			data[:last_nmea] = type
			data[:heading]	= line.shift
			
		when "ZDA"
			data[:last_nmea] = type
			data[:time]	= line.shift
			
			day		= line.shift
			month	= line.shift
			year	= line.shift
			if year.size > 2
				year = [2, 2]
			end
			data[:date] = "#{day}#{month}#{year}"
			
			data[:local_hour_offset]		= line.shift
			data[:local_minute_offset]	= line.shift
	end
	
	# Remove empty data
	data.each_pair do |key, value|
		if value.nil? || (value.is_a?(String) && value.empty?)
			data.delete(key)
		end
	end
	
	data
end

#read ⇒ Object

Parses the next NMEA sentence from the GPS and returns the current GPS data hash.



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# File 'lib/serialgps.rb', line 107

def read
	
	# Parse NMEA sentence until we find one we can use
	while true do
		nmea = next_sentence
		data = parse_NMEA(nmea)
		
		# Sentence parsed, now merge
		unless data[:last_nmea].nil?
			@collected << data[:last_nmea]
			@collected.uniq!
			@data.merge!(data)	
			
			break
		end
		
	end

	return @data
end