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What is NMEA Data?
NMEA (National Marine
Electronics Association) data is a standard language most GPS
receivers communicate with. It is an ASCII
data representation of position, satellite data and other data associated
with the GPS receiver. Below is an example of a NMEA sentence:
$GPGGA,060003,3348.784,N,11754.064,W,1,07,1.0,66.2,M,-31.9,M,,*45
This sentence contains the position of N 33'
48.784" latitude, W 117' 54.064" longitude and an altitude
of 66.2 meters. The time is showing 06:00:03 UTC.
See Also:
I see data from my GPS, but none of the controls are working
Will
your products work with USB GPS?
Yes and no. The question of USB-GPS support arises often. The reason why there are so few
standalone receivers with USB is simply that there is no native USB transmission/interface standard for GPS data.
Most GPS manufactures support a standard protocol interface called
NMEA (National Marine Electronics Association).
It was designed for RS-232 serial communication where the port is
connected to one device. Better know as peer-to-peer. A USB device can
have many devices connected to the port. USB also has manufacturer
codes and other device descriptors associated with the device
connected to the USB port. The USB standard (http://www.usb.org)
does not include a GPS device as part of the standard.
Therefore, for a manufacturer to support a GPS with a USB interface,
they must create a proprietary USB interface with that device. This
involves creating a driver for the specific operating system using a
proprietary interface. This type of model does not allow for third
party software to function with the USB-GPS device.
Some manufacturers will include an additional driver
that will make their USB-GPS device look as if it is connected to a
RS-232 serial port to software. This will allow for third party software function
with that USB-GPS assuming that the protocol is using NMEA.
I see data from my GPS, but
none of the controls are working
Most GPS receivers output a
standard protocol defined by NMEA (www.nmea.org).
This protocol holds information about the position, satellite status
and other navigation status. Some GPS receivers send a select few
commands while others have the ability to enable or disable specific
NMEA sentences.
Supported NMEA Sentences
Our products support a specific set of NMEA sentences
from the GPS receiver. They are:
| NMEA
ID |
Description |
| GGA |
Global Positioning System Fix Data - reports time,
position and fix related data |
| GSA |
GNSS DOP and Active Satellites - reports which
satellites are being used for navigation and DOP (dilution of
precision) values |
| GSV |
GNSS Satellites in View - reports the signal to
noise ratios for each satellite tracked as well as the azimuth
and elevation of each satellite |
| RMB |
Recommended Minimum Navigation Information -
Reports cross track error, destination waypoints, range to destination,
bearing, etc. |
| RMC |
Recommended Minimum Specific GNSS Data - Reports
position, speed, course over ground and date |
| ZDA |
Time and Data - reports time and date |
Some GPS manufacturers have the ability to disable NMEA output
as well as enable or disable individual NMEA sentences. Consult your
GPS manual for more information.
How can I decode the
NMEA strings and can I get source code for it?
Please refer the
NMEAParser design page for
more information.
Bluetooth
Our application will function with a Bluetooth enabled GPS receiver
only if the GPS receiver outputs NMEA data. Click here
for more information about NMEA data.
Please note that each Bluetooth device on the PC may work
differently. Some Bluetooth devices require you to establish a connection before
applications can access it using the serial port. Make sure that you
enable the connection using "My Bluetooth Places" before
using the GPS application. Also take note of the serial port used for
the client connection. Typically it is communication port 8. However
that could differ.
SiRF Chipset
Some GPS receivers use the
SiRF chipset for its GPS engine.
This chipset has can communicate to application using in its own
proprietary binary protocol or it can communicate using the industry
standard NMEA protocol. Our
products use the NMEA protocol to communicate to the GPS receiver. In
some instances, the GPS may be in SiRF binary mode. There are
utilities that allow you to change the protocol of the SiRF output to
NMEA. Check with your manufacture for more information on this.
I run
the program and nothing happens. What should I do?
Our products that communicate with a GPS
receiver expect to receive NMEA data
through a serial communications port. Make sure that the GPS receiver
is setup to output NMEA data. Some GPS receivers can communicate in
both the NMEA protocol and their own proprietary communication
protocol. The standard communication parameters are the port number
and baud rate. The port number will vary depending on the drivers and
the system. The baud rate as specified by NMEA should be 4800 baud.
However, some manufactures run at 9600 or even 57600 baud.
- Make sure that the GPS receiver support NMEA
output.
- Make sure that no other programs are
accessing the serial port. Since the serial port is a
mutual-exclusive device, only one application can access it at any
one time.
- Make sure that the communication settings are
as the manufacturer recommends.
See Also:
Supported NMEA Sentences, What is
NMEA Data?
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