Description of NMEA-0813 Data Format

NMEA-0183 is the standard format set by the National Maritime Electronics Association. The NMEA-0183 output of unified standard format adopts ASCII code, and its serial communication parameters are: baud rate = 4800bps, data bit = 8bit, start bit = 1bit, stop bit = 1bit, no parity.
The format of each statement for the NMEA-0183 is shown in the following table.

Symbol (ASCII) -- definition -- HEX--DEX
"$" -- Statement start position -- 24--36
Aaccc -- Address field. The first two are identifiers, and the last three are statement names.
"," -- Domain Separator -- 2c--44
Ddd... Ddd-data content sent
"*" -- Verification and symbol, followed by two digits: verification and -- 2a--42
Hh -- verify and
<CR>/<LF> -- Terminator, carriage return or line feed -- od, OA--13, 10

The NMEA statements provided by different gps oem receiving boards vary greatly, mainly in the meaning and position of fields. We need to first find out what information is needed, and then look for NMEA statements that include the required information against the technical information of the gps oem receiving board.

1 GPRS Mc Statement (recommended minimum specific GPS/transit data-RMC, 1 time/1 second recommended location information)
For general GPS Dynamic Positioning applications, the GPRS Mc statement fully meets the requirements. This statement includes the longitude and latitude, speed, time, and magnetic offset. The data provides sufficient information for the navigation and positioning application. The following table describes the fields in the GPRS Mc statement in detail:
$ Uplmc, <1>, <2>, <3>, <4>, <5>, <6>, <7>, <8>, <9>, <10>, <ll>, <12>

Meaning of the field $ GPRS Mc statement -- value range
<1> UTC time: hhmmss. ss -- 000000.00 ~ 235959.99
<2> Status, validity -- A indicates valid; V indicates invalid
<3> latitude format: ddmm. Mmmm -- 0000.00000 ~ 8959.9999
<4> North-South Hemisphere-N north latitude; s south latitude
<5> longitude format: dddmm. Mmmm -- 00000.0000 ~ 17959.9999
<6> Eastern Hemisphere -- e indicates the eastern longitude; W indicates the western longitude
<7> ground speed-000.00 ~ 999.999
<8> speed direction-000.00 ~ 359.99
<9> date format, month, day, year -- 010100 ~ 123199
<10> magnetic slip angle, unit: degree -- 00.00 ~ 99.99
<Ll> magnetic angle direction -- e Indicates East; W indicates West
<12> pattern indication and checksum -- A = autonomous location, D = difference, E = estimation, n = data is invalid
Example: $ gprs mc, 074529.82, A, 2429.6717, N, 11804.6973, E, 12.623, 32.122, 010806, W, A * 08

2 gpgga Statement (Global Positioning System Fix Data-GGA, GPS location information, output 1 time/1 second)
GPS positioning data. This statement includes the longitude and latitude, quality factor, hdop, elevation, reference station number, and other fields. The following table describes the fields in the gpgga statement in detail:
$ Gpgga, <1 >,< 2 >,< 3 >,< 4 >,< 5 >,< 6 >,< 7 >,< 8 >,< 9>, <10>, <ll>, <12>, <L3>, <14>

Meaning of the field $ gpgga statement -- value range
<1> UTC time: hhmmss. ss -- 000000.00 ~ 235959.99
<2> latitude, in the format of ddmm. Mmmm -- 0000.00000 ~ 8959.9999
<3> North-South Hemisphere-N north latitude; s south latitude
<4> longitude format: dddmm. Mmmm -- 00000.0000 ~ 17959.9999
<5> Eastern Hemisphere -- e indicates the eastern longitude; W indicates the western longitude
<6> quality factor-0 = undetermined, 1 = Fixed solution for GPS single point positioning, 2 = differential positioning, 3 = PPS solution, and 4 = Fixed solution for GPS; 5 = floating-point resolution of GPS data; 6 = estimated value; 7 = manual input mode; 8 = analog mode;
<7> Number of satellites at the application resolution location-00 ~ 12
<8> hdop, horizontal graphic strength factor-0.500 ~ 99.000; more than 6 unavailable
<9> antenna elevation (sea level) --- 9999.9 ~ 99999.9
<10> linear elevation unit (m) -- m
<Ll> level fluctuation: the height of the earth's elliptical sphere relative to the Earth's Level
<12> level fluctuation unit (m) -- m
<13> Differential GPS data period-differential time (the number of seconds from the last time the differential signal was received. If the difference is not located, it will be blank ).
<14> baseline station number -- 0000 ~ 1023; empty when DGPS is not used
$ Gpgga, 074529.82, 2429.6717, N, 11804.6973, E, 1.098, 42.110, M, * 76

3 gpgsv Statement (GPS satellites in view-GSV, Visible satellite information, 1 time/5 seconds)
GPS visible star azimuth, elevation, signal-to-noise ratio, etc.
Each statement can contain up to four satellites. Each satellite has four data items: (4)-Satellite Number, (5)-elevation angle, (6)-azimuth, (7)-Signal-to-Noise Ratio
$ Gpgsv, <1 >,< 2 >,< 3 >,< 4 >,< 5 >,< 6 >,< 7 >,< 8 >,< 9>, <10>, <11>, <12>, <13>, <14>, <15>, <16>, <17>, <18>, <19>

Meaning of the field $ gpgsv statement -- value range
<1> total number of GSV statement messages-0 ~ 12
<2> current GSV statement number
<3> total number of visible satellites-0 ~ 32
<4> satellite number -- 1 ~ 32
<5> elevation -- 00 ~ 90
<6> azimuth -- 000 ~ 359
<7> Signal-to-Noise Ratio-00 ~ No table in 99db, no signal received
<8> Satellite Number-1 ~ 32
<9> elevation -- 00 ~ 90
<10> azimuth -- 000 ~ 359
<Ll> Signal-to-Noise Ratio-00 ~ No table in 99db, no signal received
<12> satellite number -- 1 ~ 32
<13> elevation -- 00 ~ 90
<14> azimuth -- 000 ~ 359
<15> Signal-to-Noise Ratio-00 ~ If 99db is not found, no signal is received.
<16> satellite number -- 1 ~ 32
<17> elevation -- 00 ~ 90
<18> azimuth -- 000 ~ 359
<19> verify and, in the format of * Verify and -- check bit
$ Gpgsv, 19,192, 51,140, 37 * 7d
$ Gpgsv, 40,136, 64,266, 21,293, 168, * 4C
$ Gpgsv, 3, 3, 11, 23, 10,321, 25, 53, 7, 40, 30, 2, 46, * 48

4. $ gpvtg Statement (track made good and ground speed-Vtg, ground speed information)
Format: $ gpvtg, <1>, T, <2>, M, <3>, N, <4>, K, <5> * hh

Meaning of the field $ gpvtg statement -- value range
<1> ground heading based on zhenbei-000.000 ~ 359.999
<2> ground heading based on the magnetic north -- 000.000 ~ 359.999
<3> ground speed-000.000 ~ Section 999.999
<4> ground speed-0000.0 ~ 1851.8/hour
<5> mode indication -- A = autonomous positioning, D = difference, E = estimation, n = Invalid Data (output only in nmea0183 3.00)
<6> Hh checkpoint
$ Gpvtg, 257.314, T, 257.314, M, 10.739, N, 19.888, K, A * 2f

5. $ gpgsa Statement (gps dop and active satellites-GSA, current satellite information, 1 time/1 second)
Gsa: the current satellite and accuracy factor of GSA, including the PRN number of the visible satellite, pdop, hdop, and vdop. For example:

<1> mode -- M = manual, a = automatic.
<2> positioning type-1 = undetermined, 2 = 2D, 3 = 3D.
<3> PRN numbers: number of satellites used in the sky from Table 01 to Table 32. Up to 12 satellites can be received. The satellite number used to calculate the position (01 ~ 32 ).
<4> pdop Position Accuracy Factor-0.5 ~ 99.9
<5> hdop horizontal precision factor-0.5 ~ 99.9
<6> vdop vertical precision factor-0.5 ~ 99.9
<7> checksum. (check bit ).
$ Gpgsa, <1>, <2>, <3>, <3>, <3>, <3>, <4>, <5>, <6>, <7>
$ Gpgsa, A, 3.43, 1.67, 2.99, * 0e

6. $ gpgll Statement (output coordinate information)
$ Gpgll, <1>, <2>, <3>, <4>, <5>, <6>, <7> * 61

Field $ gpgll statement meaning -- value range
<1> latitude: ddmm. Mmmmm -- 0000.00000 ~ 8959.9999
<2> south or north latitude -- north latitude N, S south latitude
<3> longitude: dddmm. Mmmmm -- 0000.00000 ~ 17959.99999
<4> east and west longitude-east longitude E, west longitude W
<5> UTC time -- hh: mm: SS
<6> data status -- A is valid, and V is invalid.
$ Gpgll, 2431.25310, N, 11806.15429, E, 081401.00, A, A * 61

7. $ gpzda Statement (output UTC time and date information)
$ Gpzda, <1 >,< 2 >,< 3 >,< 4 >,< 5> * hh

Field $ gpzda statement meaning -- value range
<1> time: hhmmss. ss -- 0000000.00 ~ 235959.99
<2> day -- 00 ~ 31
<3> month-00 ~ 12
<4> year-0000 ~ 9999
<5> difference between local time and World Time
<6> calibration position * hh --*
$ Gpzda, 081401.00, 00*62

8. $ gpgst Statement (GPS pseudo-range noise statistics, including the standard deviation information of 3D coordinates)

Field -- Example -- Description
Sentence id -- $ gpgst
UTC time -- 024603.00 -- UTC time of associated GGA fix
RMS deviation -- 3.2 -- total rms standard deviation of ranges inputs to the navigation Solution
Semi-major deviation -- 6.6 -- standard deviation (meters) of semi-major axis of error ellipse
Semi-minor deviation -- 4.7 -- standard deviation (meters) of semi-minor axis of error ellipse
Semi-major orientation -- 47.3 -- orientation of semi-major axis of error ellipse (True North degrees)
Latitude Error deviation -- 5.8 -- standard deviation (meters) of Latitude Error
Longpolling error deviation -- 5.6 -- standard deviation (meters) of longpolling Error
Altitude error deviation -- 22.0 -- standard deviation (meters) of Latitude Error
Checksum -- * 58
$ Gpgst, 024603.00, 3.2, 6.6, 4.7, 47.3, 5.8, 5.6, 22.0*58

9. $ gpcn0 statement
Signal-to-noise ratio of each satellite used for calculation:
$ Gpcn0, 30,40, 35,26, 24,36, 31,38

Other Instructions:
Ii. output format:
Gpgga (1 time/1 second)
Gpgsa (1 time/1 second)
Gpgsv (1 time/5 seconds)
Uplmc (1 time/1 second)
Optional; GlL, Vtg, or sirf binary format

Iii. Use the coordinate system: WGS84

Dop value has three measurement types:
Horizontal, vertical, and mean ). The relationship between hdop and latitude and longitude is used as accuracy, and the relationship between vdop and altitude is measured as accuracy. pdop provides a complete level of latitude and longitude and altitude accuracy. Each DOP value is a value between 1 and 50, where 50 represents a very poor precision, and 1 represents an ideal precision.
Table 2-1 lists a specific pdop value category. Pdop Category Description:

Pdop value -- Comment -- Description
1 ~ 2 -- ideal -- this is the highest level of trust, and applications can obtain the highest accuracy at any time
2 ~ 3-excellent-trustworthy level, location measurement is quite accurate and can be applied to most applications, but some very sensitive applications won't work.
4 ~ 6 -- good -- this is the lowest level for commercial applications. Location measurement can be used for line navigation recommendations
7 ~ 8 -- moderate -- the location measurement can be used for calculation, but the quality should be improved. Recommended terms: Sky Observation
9 ~ 20 -- bottom-trust level is low. Location measurement results should be discarded or used only for rough estimation of the current location
21 ~ 50 -- difference -- the measurement results at this level are inaccurate, and there may be about half a large football field error, which should be discarded.