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How can I decode the NMEA strings and can I get source code for it?
I see data from my GPS, but none of the controls are working.
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 known 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.
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.
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.
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?