Navigation Processing with POSPac

Create new project

• Project>New default project

Import flight nav data from posatt/applanix/raw/ directory

• Project>import
• Select all the default.??? files
• "Rover Antenna Specification"
  • Manufacturer: Applanix:
  • Type: "Unknown External (Unless known!)
• Check log form inport that there are no Errors: Reports > Message Logs
  • View the "IMU Data Continuity Checking" log. If there are errors about missing data, this could have been from before the plane's take off. Try skipping the first (or more) nav files but check that the flightlines and see if this error goes away. Make sure the inported nav data covers the flight lines.

Basestations

• Import external basestation (i.e one collected by the ops team):
  • Project > Import.
    • This should only accept RINEX format data, if it is not RINEX (e.g Trimble format *.T02) then you can try using the Tools > Convert to RINEX in POSPac.

• Import OS basestations with Project "Find Base Stations"
  • I have experienced "File not found" appearing when I try and download and import basestations. So I have been downloading OS basestations myself and importing them with Project > Import

• OS basestations can be accessed vis ftp:
  • This is an example of downloading all OS basestation data from the St. Neots (SNEO) basestation for day 201 of 2021 to the current local directory:

lftp ftp://rinex.ordnancesurvey.co.uk/gps/rinex
cd 2021/201
mirror --include-glob=sneo* ./

You may need to combine multiple RINEX files into one with a command like below (this loops through the stations used for a Alconbury boresight flight and combines each station):

for station in ardl attl newr skee stee well weyb
do
  teqc ${station}222?.24o > ${station}2220.24o
done

NRT EUREF FTP:

lftp gnss.bev.gv.at:/pub/nrt/
cd 229
mirror --include-glob=KIRU* ./

Refined EUREF FTP:

lftp epncb.eu:/pub/
cd obs/2021/234
mirror --include-glob=KIRU* ./

You may also need to access Precise Ephemeris data for the basestation durations. This is not included in OS basestation data and is required for the 'IN-Fusion SmartBase' processing that is preferred if multiple basestations are available.

Precise ephemeris data can be accessed from CDDIS:

​https://urs.earthdata.nasa.gov/oauth/authorize?client_id=gDQnv1IO0j9O2xXdwS8KMQ&redirect_uri=https%3A%2F%2Fcddis.nasa.gov%2Fproxyauth&response_type=code&state=aHR0cDovL2NkZGlzLm5hc2EuZ292L2FyY2hpdmUvZ25zcy9wcm9kdWN0cy8

Naming convention is:

AAAWWWWD.sp3

Where AAA is the processing site, WWWW is GPS week, D is day of week in GPS week terms and the extension for precise ephemeris data is *.sp3 (there are also orbit and clock data available here if it is needed).

E.g esa22234.sp3 is a precise ephemeris file produced by ESA for GPS week 2223 day 4 (Thu 18 August 2022). Note that Sun = 0 and Sat = 6.

You can find out the GPS week here: ​https://www.ngs.noaa.gov/CORS/Gpscal.shtml

You may also need the broadcast ephemeris data.

GPS: ​https://cddis.nasa.gov/archive/gnss/data/daily/2023/190/23n/

GLONASS: ​https://cddis.nasa.gov/archive/gnss/data/daily/2023/190/23g/

These have anaming convention including the julian day: aaaaJJJ0.YYn e.g brdc1680.23n

Back in POSPac:

• These RINEX files (basestation observations + ephemeris data) can then be imported with Project > Import.
• If imported basestation data doesn't include ephemeris data, this also needs downloading (OS basestation RINEX data only includes the *.o file, which is just the GNSS measurements rather than the meteorological and ephemeris files).
  • Project > Find Base Stations > Select None > Tick all Precise Ephemeris and Broadcast Ephemeris rows, click "Download and Import" to download, then click "Download and Import" again to import.

Best method is 'IN-Fusion SmartBase:'

Criteria:

• At least four basestations
• Precise ephemeris data
• The flight is within the perimiter of these stations
• The flight doesn't exceed 100km from a basestation
• See POSPac manual Chapter 9 for more infomation

Method:

• Project > SmartBase Quality Check
• If the quality is good, then it will prompt you to continue to the Applanix SmartBase (ASB) stage which will run when 'Continue' is clicked.

Otherwise try 'IN-Fusion Single Base:'

Criteria:

• Single basestation
• Basestation within 30km from start of flight
• Flight within 100km of basestation

Method: Note that multiple basestaions are not supported for RINEX version 3. For RINEX version 3, single base processing is required.

• Import the basestation data
• Right click on the basestation in the project explorer > Compute RTX Coordinates.
• Right click on the basestation in the project explorer > base stations, and select 'Set Base'.

GNSS-Inertial Processor:

• If using multiple basestations, use GNSS Mode: IN-Fusion Smartbase

• If using single basestation, select the 'set' base station in the "Base station" parameter.
  • In GNSS-Inertial Processor > Properties > GNSS-Intertial Processor > Lever Arms and Mounting Angles, add the appropriate lever arms.

Generate QC report:

• Reports > QC Report >

Export SBET nav file:

• Export SBET: Custom Smoothed BET

If the IMU is mounted backwards, this is where you can add the rotation offset:

• In Export, go into Properties
• In the Export heading, go into Lever Arms and Misalignments
• If the IMU is facing the back of the aircraft. Make the TZ value 180.000 deg in 'Reference to Output Mounting Angles.