Bluetooth GPS

[Gordon Burditt]

>I see, so there must be some higher-level protocol. I'm wondering if
>there's a standard for it..
>
>There's some NMEA 0183 V2.2 Standard mentioned:
>http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=3042535254&category=23381
>
>OK, here it is:
>http://www.nmea.org/pub/0183/

A NMEA sentence is an ASCII line terminated by cr-lf.
It starts with a '$', followed by a bunch of comma-separated fields,
followed by an asterisk, followed by a 2-digit hex checksum, followed
by a carriage return, followed by a line feed.  A GPS keeps spitting
these out with updated information.  Mine is a USB device that converts
RS232 to USB.  It is recognized by FreeBSD as a ugen device, but
I can still use it just reading stuff out of the device.

The first field describes what's in the rest of it.  Fields other
than the first may be null, that is, no characters between the commas.

Some sample GPS output (blank lines inserted at roughly second
boundaries).  Yours may vary as to which sentences are
generated.  Trailing CR's deleted for posting.

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011013,3240.1042,N,09727.3699,W,1,06,0.84,207.3,M,-23.5,M,,*4B
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.54,0.84,1.30*08
$GPGSV,3,1,11,27,69,348,37,31,55,060,43,13,46,191,38,08,42,319,41*7B
$GPGSV,3,2,11,28,29,268,32,03,23,045,31,01,22,169,00,11,19,137,26*73
$GPGSV,3,3,11,02,10,067,00,07,02,212,00,10,02,299,00*4E
$GPRMC,011013,A,3240.1042,N,09727.3699,W,0.165,168.8,230803,5.6,E*66

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011014,3240.1042,N,09727.3700,W,1,06,0.84,207.4,M,-23.5,M,,*4A
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.54,0.84,1.30*08
$GPRMC,011014,A,3240.1042,N,09727.3700,W,0.040,269.0,230803,5.6,E*6C

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011015,3240.1041,N,09727.3700,W,1,06,0.84,207.5,M,-23.5,M,,*49
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.54,0.84,1.30*08
$GPGSV,3,1,11,27,69,348,35,31,55,060,41,13,46,191,37,08,42,319,40*75
$GPGSV,3,2,11,28,29,268,30,03,23,045,30,01,22,169,00,11,19,137,26*70
$GPGSV,3,3,11,02,10,067,00,07,02,212,00,10,02,299,00*4E
$GPRMC,011015,A,3240.1041,N,09727.3700,W,0.092,156.9,230803,5.6,E*67

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011016,3240.1041,N,09727.3700,W,1,06,0.84,207.5,M,-23.5,M,,*4A
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.54,0.84,1.30*08
$GPRMC,011016,A,3240.1041,N,09727.3700,W,0.209,23.1,230803,5.6,E*5F

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011017,3240.1042,N,09727.3699,W,1,06,0.84,207.7,M,-23.5,M,,*4B
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.55,0.84,1.30*09
$GPGSV,3,1,11,27,69,348,35,31,55,059,41,13,45,191,37,08,42,320,39*78
$GPGSV,3,2,11,28,29,268,31,03,23,045,31,01,22,169,00,11,19,136,27*70
$GPGSV,3,3,11,02,10,067,00,07,02,213,00,10,01,298,00*4D
$GPRMC,011017,A,3240.1042,N,09727.3699,W,0.346,63.6,230803,5.6,E*55

$PRWIZCH,01,2,28,7,08,7,31,7,13,7,02,2,10,2,03,7,07,0,11,2,27,7,00,0*4C
$GPGGA,011018,3240.1042,N,09727.3699,W,1,06,0.84,208.0,M,-23.5,M,,*4C
$GPGSA,A,3,28,08,31,13,03,27,,,,,,,1.55,0.84,1.30*09
$GPRMC,011018,A,3240.1042,N,09727.3699,W,0.114,77.1,230803,5.6,E*5D



$GPGGA,011016,3240.1041,N,09727.3700,W,1,06,0.84,207.5,M,-23.5,M,,*4A

GPGGA is one of the more useful outputs.
Field 1: GPGGA
Field 2: Time, in form HHMMSS, in UTC.
Field 3: Latitude, in degrees, minutes, and fractional minutes.
	Format DDMM.MMMM or DMM.MMMM  .  There may be any number of
	digits after the decimal point.  3240.1041 = 32 degrees, 40.1041
	minutes.
Field 4: Latitude direction (N or S)
Field 5: Longitude, in degrees, minutes, and fractional minutes.
	Format DDDMM.MMMM or DDMM.MMMM or DMM.MMMM .  There may be any number
	of digits after the decimal point.  09727.3700 = 97 degrees, 27.3700
	minutes.
Field 6: Longitude direction (E or W)
Field 10: Altitude
Field 11: Altitude units (M = meters)

$GPRMC,011018,A,3240.1042,N,09727.3699,W,0.114,77.1,230803,5.6,E*5D

GPRMC is another useful one.
Field 1: GPRMC
Field 2: Time, in form HHMMSS, in UTC
Field 3: Fix valid (A = yes, V = no)
Field 4: Latitude, in degrees, minutes, and fractional minutes.
	Format DDMM.MMMM or DMM.MMMM  .  There may be any number of
	digits after the decimal point.  3240.1041 = 32 degrees, 40.1041
	minutes.
Field 5: Latitude direction (N or S)
Field 6: Longitude, in degrees, minutes, and fractional minutes.
	Format DDDMM.MMMM or DDMM.MMMM or DMM.MMMM .  There may be any number
	of digits after the decimal point.  09727.3700 = 97 degrees, 27.3700
	minutes.
Field 7: Longitude direction (E or W)
Field 8: Speed, in knots
Field 9: Compass heading, in degrees
Field 10: Date, in form DDMMYY  (Note that the date goes with
	the time in UTC).  230803 = Aug 23, 2003
Field 11 & 12: magnetic deviation from true north (degrees), 
	and direction (E or W).

The types beginning with GP are standard.  PRWIZCH is a private
manufacturer's sentence (P) by Rockwell (RWI), and ZCH here gives
info about which receiver (of 12) is tuned to which satellite.

GPGSA tells about satellites being actively used.  They are numbered
1-32, and some of them don't actually exist.  I think there's
actually 28 in service at the moment.

GPGSV tells about satellites in view (4 to a sentence, and since
there are usually more than 4 satellites in view, the above shows
them in 1 of 3, 2 of 3, and 3 of 3 variants).  A satellite in view
is theoretically above the horizon, but may be unusable for many
reasons, such as being obstructed by buildings or mountains, too
much noise, too low on the horizon, etc.  When the GPS has had time
to find its satellites, satellites in view is typically 7-12.

					Gordon L. Burditt