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NMEA 0183

Microsoft MapPoint can work with any GPS receiver that supports the NMEA 0183 2.0 standard. The NMEA 0183 standard is a standard developed by the US National Marine Electronics Association (NMEA) to allow communication between various marine electronic devices – eg. sonar, compass, autopilot, GPS. The standard is rather dated and uses simple ASCII one line sentences transmitted over an RS-232 serial line. Despite this, the standard has become the only de facto standard for GPS receivers in the non-marine domain.

Most modern PCs and GPS receivers do not have physical RS-232 connectors, so they work with a physical USB connector and vendor-supplied driver software that makes it appear to be connected with an RS-232 (“COM port”) connection. In order to use your GPS receiver with Microsoft MapPoint, you will need to install the driver supplied with your receiver.

NMEA 0183 Serial Configuration

NMEA 0183 compliant devices work at 4,800 bps with 8 data bits, no parity, no handshake, and 1 stop bit. Some devices support different bit rates, but 4,800 is recommended for use with MapPoint.

NMEA Sentences

NMEA supports a range of different one line ‘sentences’ that report data measurements in a comma separated format. GPS information is transferred using sentences that start with the letters ‘GP’. Here is an example of a GPGGA ‘GPS Fix’ sentence that transfers a location measurement:

 $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47

Where:
     GGA          Global Positioning System Fix Data
     123519       Fix taken at 12:35:19 UTC
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     1            Fix quality: 0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
			       4 = Real Time Kinematic
			       5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
			       7 = Manual input mode
			       8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84
                      ellipsoid
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *

The full NMEA specification including all the sentence formats can be purchased from the US National Marine Electronics Association. A number of reverse-engineered versions exist, including this one by Dale DePriest.

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