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