Novatel Base GPS units

gps-base-posave-30min novatel script

• This script has the base station run for 30 minutes before corrections are sent, allowing more time to get a more accurate base position before sending RTK corrections to the Rover (we also have a 3 minute script that can be used for testing).

gps-base-posave-30min novatel script

• This script should be loaded into a Novatel Smart-V1 base GPS in order to provide RTK/DGPS corrections to a rover GPS. When the GPS is powered up, it will average position for 30 minutes, then will fix its position and start transmitting corrections via COM2 (connector J3) to a rover GPS via FreeWave or Bluetooth radios.

• Page numbers refer to the Novatel OEMV Firmware Reference Manual.

• The base GPS does not need a computer interfaced to it unless the operator wants to check on the configuration or message values (which is done using the COM1/J2 connection at 38400 baud, or USB1 or USB2). The only required connection is to a Freewave or Bluetooth radio to transmit the corrections to the rover GPS through COM2/J3 . For convenience, the USB3 port has log messages in text form at a slow rate that duplicate the faster messages sent from base to rover GPS.

• For loading a script to the GPS, the line endings need to be DOS-style (CR+LF). Opening and saving the script in Windows Wordpad should be sufficient to ensure this. Copy and paste from a browser page should also be sufficient.

the script:

   unlogall
   
   posave 0.5 0.01 0.05
   sbascontrol enable auto 0 zerototwo
   
   com com1 38400
   com com2 115200
   
   interfacemode com2 none rtca off
   interfacemode usb1 novatel novatel on
   interfacemode usb2 novatel novatel on
   
   log com2 rtcaobs ontime 1
   log com2 rtcaref ontime 10
   log com2 rtca1 ontime 5
   log com2 rtcaephem ontime 10 1
   
   log usb3 rtcadataobs ontime 10
   log usb3 rtcadataref ontime 10 2
   log usb3 rtcadata1 ontime 10 4
   log usb3 rtcadataephem ontime 10 6
   
   saveconfig
   
   log loglist
   log comconfig

• line-by-line annotations:

unlogall

   *The unlogall command (p 216) releases any log commands that may already be set, e.g., perhaps automatically by the Novatel CDU utility. For the Novatel GPS receivers, logging means producing output on one or more ports.

posave 0.5 0.01 0.05

   *posave (p 161), the position average instruction, causes the GPS to average position until one of the conditions are met, after which the FIX POSITION (p 115) command is automatically invoked. The parameters are:

       maxtime = 0.5 hours
       maxhstd = 0.01 meters
       maxvstd = 0.05 meters

   The second and third parameters are target horizontal and vertical deviations in meters, here 1 and 5 cm respectively, while the first is the maximum time in hours to wait if the target deviation values are not achieved. These deviations are not realistic, so the time limit will control. Instead the deviations if anything represent a hoped-for ideal.

sbascontrol enable auto 0 zerototwo

   *sbascontrol (p 187) sets the Satellite Based Augmentation System corrections. The parameters are:

       keyword = ENABLE (or DISABLE)
       system = AUTO (or ANY, WAAS, EGNOS, MSAS)
       PRN = 0 (or 120-138)
       testmode = ZEROTOTWO (or NONE, IGNOREZERO)

   These enable SBAS corrections; allow the GPS to choose which SBAS system to use; use any available augmentation platform; and interpret Type 0 messages as Type 2 (whatever that means).

com com1 38400

   *COM (p 87) port configuration.

   The port COM1 (connector J2) connection to a computer at 38400 baud is optional for the base GPS, but is available if the operator wants to query the base GPS for any reason, or perhaps to upload a new script.

com com2 115200

   Port COM2 (connector J3) is used to transmit RTK corrections at 115200 baud from the base GPS to a rover GPS on the boat via FreeWave or Bluetooth radio pairs.

interfacemode com2 none rtca off

   *interfacemode (p 135) sets the mode of operation of the specified com port, and must appear after the COM command if used (because COM will reset the interface mode).

   Here we configure COM2/J3 to transmit RTCA corrections from the base GPS via FreeWave or Bluetooth radios.

       port = COM2
       rxtype = none
       txtype = rtca
       responses = OFF

interfacemode usb1 novatel novatel on interfacemode usb2 novatel novatel on

   Here we configure two of the three USB interfaces to use novatel mode, which means they will accept commands and output logs.

       port = USB1, USB2
       rxtype = novatel
       txtype = novatel
       responses = ON

log com2 rtcaobs ontime 1 log com2 rtcaref ontime 10 log com2 rtca1 ontime 5 log com2 rtcaephem ontime 10 1

   LOG (p 143) configures the GPS to output information on the specified port and at a given rate and offset. This group of log commands defines what information is sent from the base GPS to the rover GPS via port COM2 (connector J3).

   RTCA messages (p 423) are designed to support aviation precision instrument approaches, and have some improvements over the RTCM messages.

   The RTCAOBS (p 430) message contains base station satellite observation information, with one line per satellite, so that the rover GPS can correct the range observations for those satellites.

   The RTCAREF (p 435) message contains base station position information, and should be sent every 10 seconds (as done here).

   RTCA1 messages, RTCA Standard Type 1 messages, are sent every 5 seconds from the base to the rover GPS.

   RTCAEPHEM messages are sent every 10 seconds plus an offset of 1 second from base to rover GPS. They contain raw satellite ephemeris information.

log usb3 rtcadataobs ontime 10 log usb3 rtcadataref ontime 10 2 log usb3 rtcadata1 ontime 10 4 log usb3 rtcadataephem ontime 10 6

   This group of log messages provide the same information as the above GPS-to-GPS messages, but at a slower rate so that an operator can see what's happening more easily. The DATA term in the message name provides more verbose output, so that, e.g., bit fields are broken out as separate values.

   The various messages are output every 10 seconds, offset 2 seconds apart, on the USB3 port.

saveconfig

   *SAVECONFIG (p 187) writes the configuration into non-volatile memory, so that the configuration remains after power is lost and restored.

log loglist

   *LOG LOGLIST (p 355) displays the configured log messages, ports, rates, and offsets for information only.

log comconfig

   *LOG COMCONFIG (p 291) displays the ports configuration for information only.

• general notes

• To load a script, connect to a suitable port on the GPS using a terminal emulator program, e.g., HyperTerminal, Putty, Minicom (linux), etc.. A suitable port is one that is set to receive in novatel mode, so that commands will be accepted; COM1/J2, USB1, or USB2 are available with this configuration. To test for this, type a command that will produce output, e.g., log loglist, log bestpos, or even just log; if a response is seen then commands should be accepted on that port.

• To use the USB ports from the Novatel GPS on a computer, the Novatel driver must be installed, and then the mapping of the three Novatel USB interfaces to a COM number on the computer has to be determined. CSI DevConfig can be used for this (click on the elipses for "Unknown", ... next to the 'PC Serial Port' box), and will be on the project computers (Toughbook laptops), or the Windows System Device Manager, Ports tab can be used. There should be three Novatel USB Virtual Serial Ports, most likely in consecutive order, but possibly mapped to different numbers than for a previous session.

• Note that the Novatel serial com ports are wired as DCE (data communications equipment), so can connect to a DTE (data terminal equipment) serial port on a computer (laptop) with a straight-through cable. The Freewave radio modem is also DCE, so a null modem cable needs to be used for the GPS COM2/J3 connection to the modem.

• Note that typed characters will not be echoed by the novatel GPS, so it may appear that the interface is not working unless a valid command (i.e., one that will generate a response) is entered. (The log command with no argument should produce an error message, but that's good enough for this pupose.)

• Note that the function of the POSAVE (position average) instruction is to control how long the GPS averages its position before the FIX POSITION command is automatically invoked. If the base GPS will occupy the same location each day, then a script can be made with POSAVE instruction replaced by FIX POSITION (p 115) with position data, e.g., obtained using the LOG BESTPOS novatel command, perhaps after using POSAVE with a very long maxtime hours value.

Troubleshooting Base

• check to see that the freewave or bluetooth radio lights are working.
• Remember, you are looking for a quality 9 (WAAS) or quality 5 (RTK)
• check battery voltage and change batteries
• Reload the program in hyperterminal
• if the program doesn't seem to be loading properly, open in Wordpad and save. Then copy/paste to host in hyperterminal.
• log bestpos while in USB2 (in hyperterminal) of the base can give you a little information.