Leica IPAS TC navigation processing

IPAS TC combines the IPAS Pro and Graftnav into one process.

All files should be named according to the year, julian day and flight letter (where applicable) - YYYYJJJf.*

When you have found the best solution re-process the navigation to create a sol file for the RCD. Change the lever arm values to those for the RCD (all lever arm values here) and the output sol file to *_camera.sol.

Setting up the Project

1. Make sure you have done the base station verification.
2. Open IPAS TC
   1. Select new, navigate to the ipas folder of the relevant project, and give your project a name as above and click create
   2. This will create a *.itp file which will store all the parameters used
   3. This brings you to the Project Overview dialog box
3. Select Aircraft Data File
   1. The Data File should point to ipas/raw/*.000 file
   2. The Extract Directory should be created automatically as ipas/extract, if not create it
   3. Click Extract Raw data. When that has finished, check the messages for any errors and click accept
4. This will automatically bring you to the GNSS Base Station dialog box
   1. Under Options for GNSS select User Differential GNSS (for PPP see below)
   2. From here you can select Add Base Station or Download Service Data
   3. Up to 8 base stations can be added
   4. To add a base station select the appropriate Raw Data Folder on the Raw GNSS File tab and click convert.
   5. Check the correct Co-ordinate and Antenna information have been added and accept
   6. When you have finished adding any additional base stations select accept
5. The final stage before processing is to set the Configuration
   1. Click on configuration
   2. Check the lever arm values under the GNSS and IMU tab are correct for your sensor.
   3. On the GNSS tab select Processing Options (small button on the far right). Use the following settings:
      1. Use GLONASS if present should be ticked
      2. Should use L2 Carrier. Disable this if the base station is less than 10km away
      3. Select Engage Only
      4. Quality Acceptance - Q2 (99%)
      5. Click OK, then accept to go back to the main Project Overview
6. Select Start Processing
   1. This will process the forwards and backwards solution, smooth the data and output the *.sol file

Note: If you get an error saying "Cannot load MANUFACT.dtm" copy the following folder C:\Users\Default\AppData\Roaming\NovAtel\IPAS_TC_3_00 to the same location under your user space.

For Windows XP the files are located under C:\Documents and Settings\Default User\Application Data\NovAtel\IPAS_TC_3_00

Analysing the Data

1. Select Launch Graphical Analysis Window
   1. Initially you will see the trajectory of the aircraft, coloured by GPS time
   2. Click on Show Toolbox
   3. Select Solution Analysis and choose which parameters you want to plot.
      1. Check the Position Separation -this should ideally be less than ±0.05m.
      2. The ambiguity fix is shown on the same plot, for a fixed solution this will be 2.
      3. Check the Position Accuracy - this should ideally be less than ±0.035m in lat/long and ±0.05m in height
      4. To change the plot setting select Tools -> Default Plot Settings.
   4. If you do not get an acceptable solution, try to change some of the settings and rerun the processing
      1. Select Windows > Project Overview > Configuration.
      2. On the GNSS tab, select GNSS processing options.
      3. Adjust the settings and try again (e.g. lower the elevation mask, change the ARTK setting)
      4. If you want to compare solutions make sure you change the output name (on the Project Overview window)
   5. If you cannot get a fixed ambiguity solution (shown on the rhs of the position seperation graph) try changing the L2C phase cycle of the basestation
      1. Go to Base/Precise GNSS file
      2. Under GPB File Information select Edit
      3. Change the value and select close
      4. Typical values are -0.25, 0.00, 0.25 and 0.50
      5. Check the leverarm values haven't been entered incorrectly.

You can also look at the IPAS solution file (to see the Lat/Long trajectory of the aircraft).

To compare two solutions select Compare Solution. You need to first create a difference file, selecting the two *.sol files you wish to use. Then load up the difference file (*.dif).

If you still cannot get a good solution, you can try processing using the old IPAS Pro ​http://arsf-dan.nerc.ac.uk/trac/wiki/Processing/IPASPro

Additonal Notes:

The intermediate processing files (e.g. *.fwd, *.rev) are stored in C:\Documents and Settings\$user\Local Settings\Temp\ie - there is a way to redirect these files elsewhere. They may be needed if we want to be able to import the result into POSPAC?

To redirect the intermediate processing files you need to change your user TEMP/TMP settings. Right click My Computer -> Properties. Select Advanced and click Environment Variables. Edit the TMP and TEMP ones to point to somewhere on the D drive (e.g. D:\temp\mark1\). Note that this update will be system wide and all programs will use it as the temp directory. The intermediate files are deleted at the end of the run.

The accuracy using IPAS TC is approximately the same as using IPAS Pro and GraftNav combined. IPAS TC can operate with fewer satellites and deeper turns => more reliable observations

Leica don't recommend using recomputing the base station position as this introduces more unknown parameters into the mix.

When you process the navigation it also produces the sol file, you cannot process them separately. If you wish to compare two sol files, remember to change the output name of the sol file.

Estimate Lever Arms

In general you don't need to select this. However, it can be used to check the accuracy of the lever arm values.
If you have good data (3 mins flight alignment, figure of 8, good satellite data) and the lever arms values are significantly off then consider remeasuring.

When Using Download Service data

If you can't get a fixed solution or fixed ambiguity check the base station settings.
Some satellites need a correction file to offset to older satellites (not applicable to the Leica stations)

If you get an error saying "Error: GPS Failed during Auto Alignment End-of-file ReachedSuggestion: Try a different start (or end) time" when trying to process, download the base station data re-sampled to 1.00 second interval.

PPP Mode

• Select use Precise Point Processing from the Setup NSS Base Station window.
  
• Click on Check Availability to see what data are available.
  
• This will display all precise data that has been found, and will be default select the final orbit.
  
• Do not use 'Final clock (30s)' - better to use 5 or 1 second data.
  

PPP mode is not recommended for project under 90 minutes.
It is not possible to estimate the lever arm in PPP mode.

Can process the base station data in PPP mode to get a fix on the co-ordinates.

User frame

The GNSS and IMU values can be changed in IPAS TC if they are incorrect. The user frame values cannot. They can be checked in ipas/extract/*extract.log. If you find these values are not correct let Ops know so they can change them to what they should be.

Troubleshooting

• Unable to save IPAS solution.
  

To a query about this error, Leica replied :
"""my findings are the following: the basestation sampling rate was 2Hz, so it is better to resample it to the 1 hz. Second thing is that you have quite big data gap in the basestation (see attached file "basestationdatagap") and the final thing is that doppler measurements on L1 in the basestation file are wrong, so I recalculate them and you can try to process your data with this gpb file (location is our ftp site /outgoing/for_ioannis). processed data combined separation you can see on the next attached file"""

From this you can take what you wish, some of those issues may or may not apply, in any case the fixed GPB file Leica provided did solve the problem.

To fix the L1 Doppler Measurement issue, go to GrafNav -> GPB utilities-> View Raw GNSS data-> Edit -> Recalculate Doppler for...