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Some time ago I bought a bluetooth GPS receiver
for my IPAQ Pocket PC, and I wanted to experiment with using a PC serial port to read the data, and
interpret the NMEA sentences.
I searched the Internet for VB Source code,
but could only find NMEA Parsers written for Java, C++ Linux etc, but nothing useful for VB.
So I decided to write my own. It is a VB
Module at the moment, but I'm hoping to create a Dll version pretty soon.
GPS Receivers generally communicate using
NMEA -0183 sentences. These are strings of data separated by commas. They have a starting identifier,
which indicates what the data is for, data separated by commas, and a terminator & checksum to
identify the end.
The data is usually available via a serial port at around 4800,N,8,1. My
Module uses the MsComm control to read the data on the required port into a
buffer. The software then breaks the data down to 4 Major types defined by VB User Types, and their
particular properties. The types and properties are as below:- |
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For example:- |
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To show the UTCTime in text1 textbox, use |
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Text1.text=GGA.strUttcTime |
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You can download an example of using the
module here. The windows binary PBGPS.exe is in
this zip. |
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If you want to drop me a line click my name
below. |
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Paul Bartlett |
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| Sentence |
Description |
| $GPGGA |
Global positioning system fixed data |
| $GPGSA |
GNSS DOP and active satellites |
| $GPGSV |
GNSS satellites in view |
| $GPVTG |
Course over ground and ground speed |
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$GPGGA Sentence (Fix data)
Example (signal not acquired):
$GPGGA,235947.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,,,,0000*00
Example (signal acquired):
$GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F |
| Field |
Example |
Comments |
GGA Property |
| Sentence ID |
$GPGGA |
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| UTC Time |
092204.999 |
hhmmss.sss |
strUttcTime |
| Latitude |
4250.5589 |
ddmm.mmmm |
varLatitude |
| N/S Indicator |
S |
N = North, S = South |
strNSIndicator |
| Longitude |
14718.5084 |
dddmm.mmmm |
varLongitude |
| E/W Indicator |
E |
E = East, W = West |
strEWIndicator |
| Position Fix |
1 |
0 = Invalid, 1 = Valid SPS, 2 = Valid DGPS, 3 = Valid PPS |
strPositionfix |
| Satellites Used |
04 |
Satellites being used (0-12) |
strSatsUsed |
| HDOP |
24.4 |
Horizontal dilution of precision |
strIIDOP |
| Altitude |
19.7 |
Altitude in meters according to WGS-84 ellipsoid |
strAltitude |
| Altitude Units |
M |
M = Meters |
strAltUnits |
| Geoid Seperation |
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Geoid seperation in meters according to WGS-84 ellipsoid |
strGeoid |
| Seperation Units |
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M = Meters |
strSepUnits |
| DGPS Age |
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Age of DGPS data in seconds |
strDgpsAge |
| DGPS Station ID |
0000 |
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strDspgid |
| Checksum |
*1F |
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| Terminator |
CR/LF |
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$GPGSA Sentence (Active satellites)
Example (signal not acquired): $GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30
Example (signal acquired):
$GPGSA,A,3,01,20,19,13,,,,,,,,,40.4,24.4,32.2*0A |
| Field |
Example |
Comments |
GSA Property |
| Sentence ID |
$GPGSA |
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| Mode 1 |
A |
A = Auto 2D/3D, M = Forced 2D/3D |
strMode |
| Fix Type |
3 |
1 = No fix, 2 = 2D, 3 = 3D |
strFixType |
| Satellite used 1 |
01 |
Satellite used on channel 1 |
strSat1 |
| Satellite used 2 |
20 |
Satellite used on channel 2 |
strSat2 |
| Satellite used 3 |
19 |
Satellite used on channel 3 |
strSat3 |
| Satellite used 4 |
13 |
Satellite used on channel 4 |
strSat4 |
| Satellite used 5 |
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Satellite used on channel 5 |
strSat5 |
| Satellite used 6 |
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Satellite used on channel 6 |
strSat6 |
| Satellite used 7 |
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Satellite used on channel 7 |
strSat7 |
| Satellite used 8 |
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Satellite used on channel 8 |
strSat8 |
| Satellite used 9 |
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Satellite used on channel 9 |
strSat9 |
| Satellite used 10 |
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Satellite used on channel 10 |
strSat10 |
| Satellite used 11 |
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Satellite used on channel 11 |
strSat11 |
| Satellite used 12 |
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Satellite used on channel 12 |
strSat12 |
| PDOP |
40.4 |
Position dilution of precision |
strPDOP |
| HDOP |
24.4 |
Horizontal dilution of precision |
strHDOP |
| VDOP |
32.2 |
Vertical dilution of precision |
strVDOP |
| Checksum |
*0A |
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| Terminator |
CR/LF |
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$GPGSV Sentence (Satellites in view)
Example (signal not acquired): $GPGSV,1,1,01,21,00,000,*4B
Example (signal acquired):
$GPGSV,3,1,10,20,78,331,45,01,59,235,47,22,41,069,,13,32,252,45*70 |
| Field |
Example |
Comments |
GSV Property |
| Sentence ID |
$GPGSV |
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| Number of messages |
3 |
Number of messages in complete message (1-3) |
strNoMessages |
| Sequence number |
1 |
Sequence number of this entry (1-3) |
strSeq |
| Satellites in view |
10 |
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strSatsInView |
| Satellite ID 1 |
20 |
Range is 1-32 |
strSatId1 |
| Elevation 1 |
78 |
Elevation in degrees (0-90) |
strElevation1 |
| Azimuth 1 |
331 |
Azimuth in degrees (0-359) |
strAzimuth1 |
| SNR 1 |
45 |
Signal to noise ration in dBHZ (0-99) |
strSNR1 |
| Satellite ID 2 |
01 |
Range is 1-32 |
strSatId2 |
| Elevation 2 |
59 |
Elevation in degrees (0-90) |
strElevation2 |
| Azimuth 2 |
235 |
Azimuth in degrees (0-359) |
strAzimuth2 |
| SNR 2 |
47 |
Signal to noise ration in dBHZ (0-99) |
strSNR2 |
| Satellite ID 3 |
22 |
Range is 1-32 |
strSatId3 |
| Elevation 3 |
41 |
Elevation in degrees (0-90) |
strElevation13 |
| Azimuth 3 |
069 |
Azimuth in degrees (0-359) |
strAzimuth3 |
| SNR 3 |
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Signal to noise ration in dBHZ (0-99) |
strSNR3 |
| Satellite ID 4 |
13 |
Range is 1-32 |
strSatId4 |
| Elevation 4 |
32 |
Elevation in degrees (0-90) |
strElevation4 |
| Azimuth 4 |
252 |
Azimuth in degrees (0-359) |
strAzimuth4 |
| SNR 4 |
45 |
Signal to noise ration in dBHZ (0-99) |
strSNR4 |
| Checksum |
*70 |
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| Terminator |
CR/LF |
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$GPVTG Sentence (Course over ground)
Example (signal not acquired): $GPVTG,,T,,M,,N,,K*4E
Example (signal acquired): $GPVTG,89.68,T,,M,0.00,N,0.0,K*5F |
| Field |
Example |
Comments |
VTG Property |
| Sentence ID |
$GPVTG |
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| Course |
89.68 |
Course in degrees |
strCourse1 |
| Reference |
89.68 |
T = True heading |
strReference1 |
| Course |
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Course in degrees |
strCourse2 |
| Reference |
89.68 |
M = Magnetic heading |
strReference2 |
| Speed |
0.00 |
Horizontal speed |
strSpeed1 |
| Units |
N |
N = Knots |
strSpeedUnit1 |
| Speed |
0.00 |
Horizontal speed |
strSpeed2 |
| Units |
K |
K = KM/h |
strSpeedUnit2 |
| Checksum |
*5F |
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| Terminator |
CR/LF |
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Starter |
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