GPS Configuration

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The GPS Configuration tab allows setting of various parameters such as serial communication, PPS Settings and other parameters.

Communications Settings

The communication settings parameters allow the configuration of both the serial port as well as the baud rate. The standard NMEA baud rate is 4800 baud. If for some reason the GPS receiver connected to the PC communicates at a different baud rate, use this parameter to set the baud rate. The COM Port parameter reflects the serial communication port settings that the GPS unit is connected to.

PPS Settings

LGPSTime has the ability to configure the 1PPS triggering. This frame needs for select the RS-232 hardware line to be used as the 1PPS trigger.

Use 1 Pulse Per Second from GPS receiver

When this check-box is selected, LGPSTime waits for the RS-232 DSR or CTS line to change state before setting the PC clock. If the GPS receiver outputs a 1PPS signal, this signal can be feed back to the DSR or CTS line to maximize the synchronization accuracy to the PC.

 

Use CTS / Use DSR

Selects the RS-232 hardware line to be used as the 1PPS input.

 

Refresh

Click this button for check availability of the 1PPS signal on DSR or CTS line.  Answer is shown in sting State and can be the following:

Unknown

To define the state of line is impossible.

Getting the state...

Definition of the line state in process.

No PPS signal

There was no signal 1PPS on the RS-232 DSR or CTS line

PPS signal is present

There is a signal 1PPS on the RS-232 DSR or CTS line

 

Debug View

 

Show the received NMEA data - Click this check-box if you want to see the raw data in NMEA format received from COM port.

This NMEA (The National Marine Electronics Association) data includes the complete PVT (position, velocity, time) solution computed by the GPS receiver. The idea of NMEA is to send a line of data called a sentence that is totally self contained and independent from other sentences. Each sentence begins with a '$' and ends with a carriage return/line feed sequence and can be no longer than 80 characters of visible text (plus the line terminators). The data is contained within this single line with data items separated by commas. The data itself is just ascii text and may extend over multiple sentences in certain specialized instances but is normally fully contained in one variable length sentence. The data may vary in the amount of precision contained in the message. There is a provision for a checksum at the end of each sentence. The checksum field consists of a '*' and two hex digits representing an 8 bit exclusive OR of all characters between, but not including, the '$' and '*'. A checksum is required on some sentences.

NMEA consists of sentences, the first word of which, called a data type, defines the interpretation of the rest of the sentence. Each Data type would have its own unique interpretation and is defined in the NMEA standard.

LGPSTime use only the following sentences: GPGGA (Essential fix data which provide 3D location and accuracy data.) and GPRMC (The Recommended Minimum of essential gps pvt (position, velocity, time) data).

NMEA sentences look similar to:

$GPRMC,114738.000,A,5508.5957,N,06009.1984,E,1.26,73.90,131108,,*34

$GPGGA,114739.000,5508.5953,N,06009.1985,E,1,05,1.8,338.2,M,-10.7,M,,0000*70