How do I configure a Position Output on port P1 of my LD2/LD2S?

This port offers a choice of NMEA positions computed from two different sources:

• When “LOCAL” is selected, the NMEA position is computed in a separate processor within the LD2 using VERIPOS algorithms.
• When “GPS RX” is selected, the NMEA position data is computed within the GPS receiver itself.  This setting is only used when an accurate timing message (ZDA) is required. Usually in conjunction with 1PPS.

VERIPOS recommend using “LOCAL” as the default setting. Contact the VERIPOS Helpdesk if further information is required.

Note:

1. The VERIPOS algorithms compute a position based on the closest reference stations enabled on the RTCM output from port P2. (Up to 4 stations are utilised.) The processor therefore computes the optimum position available from the selected stations, regardless of whether all stations are enabled or just a single station.
2. It may be necessary to configure different or additional NMEA messages in the output string.
   In “LOCAL” mode, messages can easily be selected using the LD2 menu system.
3. When in "LOCAL" mode, the RS232 output format is fixed at: 9600 baud, 8 data bits, no parity and 1 stop bit. (8-N-1)
4. In order to output LOCAL NMEA data from ports P2, P3, or P1 (in LOCAL mode), P5 must be set to “OFF”. 

1. Selecting the Position Output Mode

Repeatedly press *Page* to reach the entry point of the main menu:

Press the *Enter* then press *Page* twice. The following screen is shown:

Press the *Enter* key to select the first page of the Serial Port configuration menu, Port P1:

This screen is used to select the source of the NMEA output message. The options are “GPS RX” or “LOCAL”.

Press *Toggle* until the required option is displayed then press *Enter* to select it.

2. Configuring the Output Strings

• When “GPS RX” is selected, the NMEA messages can only be selected by reconfiguring the GPS receiver using the manufacturer's software application.
• When “LOCAL” is selected, the NMEA messages can be selected using the LD2(S) keyboard and display, as described below.

Repeatedly press *Page* to reach the entry point of the main menu:

Press *Enter* followed by *Page* to display the GPS Receiver Configuration menu:

Press *Enter* then press *Page* 4 times to display the Port A Settings menu:

Press the *Enter* to access the first screen in the sub-menu which is shown below:

Press *Enter* to move the cursor to the centre of the screen (NMEA selection mode).

Use the *Toggle* key to move through the list of available NMEA strings.

It is possible to output multiple messages from P1. Each message may be individually enabled or disabled.

To the right of each string ID, the display will show either “OFF” (indicating that it is disabled) or “1.0” (indicating that it is enabled for output at 1 second intervals).

To change the status of the displayed string, press *Enter*.

This will move the cursor to the right of the screen. (Rate selection mode).

Note: For the front panel “GPS” and “DGPS” indicators to be activated either a GGA or a GGX string must be enabled.

The number displayed to the right of the cursor is the output rate for the string. 

To disable the string, press *Toggle* until “OFF” is displayed. 

To enable the string, press *Toggle* until any other rate is displayed.

Note: The configuration menus offer a choice of rates but these are not fully implemented.
Selecting any value except “OFF” will enable the message at the one second rate.

Press *Enter* to accept the entry and move back to the string selection mode.

Note:

1. The NMEA messages selected in *Port A Settings* will also be output on port P2 when it is configured in “LOCAL” mode.
2. **GPS Receiver**, *Port B Settings* may be configured in a similar manner to that described above. These settings determine the NMEA messages output on port P3 when it is configured in “SKT” mode. Refer to manual for further details.

The LD2 can be configured to output the following NMEA messages, either individually or in combination:

Note:

GGA is the standard positioning message containing essential fix data which provides 3D location and accuracy information.

GGX is similar to GGA but latitude and longitude are specified with increased accuracy (7 characters after the decimal point instead of 5). Because of the increased message length, some systems may be unable to decode it.

These messages are described in detail in the Appendix of the Operations Manual. The manual may be viewed or downloaded from this Web site.