Basic NMEA Sentence formats (was: GPS input and GRASS)

[Clifton Wood]

Jill and Venkatesh:

The NMEA 0183 data format varies from GPS unit to GPS unit since most
manufacturers like to insert their own proprietary extensions to the
format, but here are a few of the standard message sentences which
should be available on most units that claim NMEA complaince:

"<>" denotes Carriage Return & Line-Feed pair.

__GGA = Global Positioning Fix Data


__GGA,hhmmss.ss,ddmm.mmmm,n,dddmm.mmmm,e,q,ss,y.y,a.a,z,g.g,z,t.t,iiii*CC<>

		hhmmss.ss = UTC of position fix
			hh = hours (00-24)
			mm = minutes (00-59)
			ss.ss = seconds (00.00-59.99)

		ddmm.mmmm,n = latitude
			dd = degrees (00-90)
			mm.mmmm = minutes (00.0000-59.9999)
			n = direction - N - North; S - South
	
		dddmm.mmmm,E = longitude
			ddd - degrees (000-180)
			mm.mmmm - minutes (00.0000-59.9999)
			e = direction - E - East; W - West

		q = GPS quality indicator
			0 - GPS not available
			1 - GPS available
			2 - GPS differential fix

		ss = number of satellites used (0-12)

		y.y = HDOP

		a.a,z = antenna height
			a.a = height
			z = units	M - Meters

		g.g,z = Geodial Separation
			g.g = height
			z - units	M - Meters

		t.t = Age of differential data

		iiii = differential ref. station ID (0000-1023)

		CC = checksum (hex 00-7F)


__CSA = Geographic Position - GPS DOP and Active sattelites

	__GSA,a,b,cc,dd,ee,ff,gg,hh,ii,jj,kk,mm,nn,oo,p.p,q.q,r.r*CC<>


		a - sat acquisition mode	M - Manual
						A - Automatic

		b - pos mode			1 = fix not avail
						2 = 2D
						3 = 3D

		cc,dd,ee,ff,gg,hh,ii,jj,kk,mm,nn,oo	sat ids used in solution
							(null for unused fields)

		p.p = PDOP	(1.0-9.9)
		q.q = HDOP	"
		r.r = VDOP	"

		CC = checksum (hex 00-7F)

__RMC = Recommended Minimum Specific GPS

	__RMC,hhmmss.ss,a,ddmm.mmmm,n,dddmm.mmmm,w,z.z,y.y,ddmmyy,d.d,v*CC<>

		hhmmss.ss = UTC of position fix (see GGA)

		a = status	A - valid
				i -  invalid

		ddmm.mmmm,n - Latitude (see GGA)

		dddmm.mmmm,e - Longitude (see GGA)

		z.z = Speed over ground (knots)

		y.y = track made good	(0.0-359.9; reference to true north)

		ddmmyy = UTC date of position fix
			dd = day (01-31)
			mm = month (01-12)
			yy = year (00-99)

		d.d = magnetic variation (0.0-180.0; degrees)

		v = variation sense	E - East
					W - West

		CC = checksum (hex 00-7F)

__GSV = GPS Satellites in View

	__GSV,t,m,n,ii,ee,aaa,ss,ii,ee,aaa,ss,ii,ee,aaa,ss,ii,ee,aaa,ss*CC<>

		t = Total number of messages (1-3)

		m = message number (1-3)

		n = total number of satellites in view
	
	For each visible satellite, 4 groups per message
		ii = satellite PRN number
		ee = elevation (0-90; degrees)
		aaa = asimuth (0-359; degrees true)
		ss = signal to noise ratio (0-99; dB)
	
		CC = checksum (hex 00-7F)


Not all GPS units that claim NMEA compliance will support ALL of these
formats except
for GGA (which is universal, I think...)

Good luck!

- Cliff

PS - I don't know how up to date this is, but since I can't find info on
the format fro NMEA's own pages (http://www.nmea.org/), this is the best
I can do for the moment.

-- 
============================================================
Clifton B. Wood
Programmer/Analyst for the Entomology Dept. of Va. Tech.
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