Author

Max Lapshin (max@maxidoors.ru)

Copyright

Copyright © 2007 Max Lapshin, Getalime

License

Distributes under the same terms as Ruby

To use NMEA parser, you should somehow get data stream from Yor gps device. For example, You can use ruby-serialport (which seems to be dead, but working). The example on Mac with installed USB-Serial driver:

require ‘serialport’ require ‘nmea’ @sp = SerialPort.open(“/dev/tty.usbserial”, 4800, 8, 1, SerialPort::NONE) @handler = NMEAHandler.new while(@sentence = @sp.gets) do NMEA.scan(@sentence, @handler) end

NMEAHandler is a user class, that implements following interface:

class NMEAHandler def rmc(time, latitude, longitude, speed, course, magnetic_variation) # read further about types of latitude and longitude end def gsv(flag, satellites) end def gsa(mode_state, mode, satellites, pdop, hdop, vdop) end def gga(time, latitude, longitude, gps_quality, active_satellite_count, gsa_hdop, altitude, geoidal_height, dgps_data_age, dgps_station_id) end end

As you can see, the following NMEA sentences are supported currently: $GPRMC, $GPGSV, $GPGSA, $GPGGA. If you need more, please contact me and provide me with several examples. I will add support for them. NMEA::scan will not try to call unexistent method on your handler, thus you can implement only those methods in your handler, you need to.

GSV handler has parameter flag. This flag can take one of the following values: :start, :continue

and <code>:finish</code>. GSV messages appears in packs of several sentences, but NMEA::scan is stateless,

thus your NMEAHandler should keep accumulate these messages.

It is important to mention, that NMEA::scan assumes, that You have classes GPS::Latitude and GPS::Longitude, which initializer, takes two arguments: degrees and minutes. You can use this example:

module GPS AngleValue = Struct.new :degrees, :minutes

class AngleValue def to_s “%d %.4f%s” % [degrees.abs, minutes, symbol] end end

class Latitude < AngleValue def symbol degrees >= 0 ? “N” : “S” end end class Longitude < AngleValue def symbol degrees >= 0 ? “E” : “W” end end end

Supported devices.

Ruby NMEA has full support of Globalsat BU-353 device (www.usglobalsat.com/item.asp?itemid=60&catid=17).

NMEA syntax is assumed to be as in document nmea.html, taken from www.werple.net.au/~gnb/gps/nmea.html