Data Hacking

202 Part III — Data Hacking
GSA (GPS DoP and Active Satellites)
This sentence provides detailed information on the satellite fix. It includes the numbers of the
satellites being used in the current solution and the dilution of precision (DoP). DoP is an
indication of the effect of satellite geometry on the accuracy of the fix. DoP has no units of
measure — it is a case of smaller is better.
$GPGSA,A,B,x1,x2,x3,x4,x5,x6,x6,x8,x9,x10,x11,x12,x,y,z*hh
A Fix mode:
M = Manual (where the receiver is forced to work in 2D or 3D)
A = Automatic
B Fix mode:
1 = Fix not possible
2 = 2D
3 = 3D
x1 – x12 IDs of satellites (SVs) used for position fix
z Positional dilution of precision
y Horizontal dilution of precision
z Vertical dilution of precision
*hh Checksum
GSV (Satellites in View Data)
This is a very interesting and informative NMEA sentence. Satellites in view shows data about
the satellites that the unit might be able to find based on its viewing mask and almanac data. It
also shows the unit’s current ability to track this data.
One GSV sentence can provide data for up to four satellites, so three sentences may be needed
for the full information. The GSV for all satellite sentences do not need to appear in sequence.
$GPGSV,A,B,C,D1,E1,Az1,SNR1,D2,E2,Az2,SNR2,D3,E3,Az3,SNR3,D4,E4,
Az4,SNR4*hh
A Number of messages required to hold data on all SVs in view
B Message number
C Total number of satellites in view
D1-D4 Satellite PRN number
E1-E4 Elevation in degrees (90 maximum)
Az1-Az4 Azimuth (measured in degrees from True north, 000 to 359)
SNR1-SNR4 Signal-to-noise ratio (the higher the number the better the signal)
*hh Checksum