Requires an LP360 Drone license.

Generating the lidar point cloud and orthophoto from the source data requires that the data be correctly positioned using the trajectory of the drone.  This is a post-processed kinematic (PPK) solution accomplished using one of several GNSS post processing software engines fully integrated into LP360's Trajectory Processing wizard on the Sensor tab of the LP360 ribbon to combine the GNSS observations, both base and in-air, with the angular and acceleration data recorded by the onboard inertial measurement unit (IMU) in the position and orientation system.

How to Create a Post-Processed Trajectory File

Input Settings Page

1. Check the Cycle section to validate the correct cycle name and raw position file are being referenced. If you are using the default folder structure, these should not need to be changed.

Processing Range

LP360 Drone will attempt to automatically set the start/end time for the sensor trajectory processing based on the kinematic motion of the sensor. This works in the vast majority of cases, however, there are times where the user may want to change the start time of processing due to a mismatch of when the sensor and base station observation started or GNSS issues with either the sensor or base station during the beginning or ending of the flight. If you are unsure about what time to change, look at your current Post Process Trajectory Report, or generate one with the QC-Only (Realtime) option, and use the charts to determine areas where you may want to exclude due to GNSS data quality issues.

2. Select the Processing Mode you want to use to calculate your positions. See a comparison of the Processing Modes for post processing the sensor trajectory.

Single Base: Single Base Positioning is a GNSS processing mode where a single dedicated base station is employed to provide differential corrections to the rover GNSS receiver. 

SmartBase: Applanix SMARTBase is a web service that uses existing ephemeris data from public base station infrastructure around the world to generate a virtual base station at your trajectory.

PP-RTX: PP-RTX (Post-Processed Real-Time Extended) is a GNSS processing mode that utilizes Trimble® CenterPoint™ RTX technology. It provides centimeter-level post-processed positioning accuracies without requiring local reference stations.

QC only (Realtime): If available for your system, use this mode for field checks to verify the quality of the rover data. 

3. You need to select which Run Location you intend to use for processing:  

• • • If you intended to run using a local desktop copy of POSPac UAV, select Local. This will require a licensed copy of POSPac UAV installed on the processing machine. Local processing with an owned/purchased TrueView sensor does not use LP360 Points from your pool.

    • If you want to use cloud-based processing, select Cloud and enter/verify your LP360 Online login information is correct.  All cloud-based processing is subscription-based and may use LP360 Points from your pool as presented in the cost estimate.

4. GNSS Settings

5. Review the Cycle Summary section. If using TrueView Points, an estimate for the job plus your current account balance will be shown.

6. Click Next.

Base Station Settings Page

1. Verify the path for the Base Station Observation File(s) is correct.  This is the observation file you downloaded from the base station and copied to the Cycle\System folder on the USB. It was automatically moved to your project folders during the import and project set-up.  If you did not copy the observation file to Cycle\System earlier, you will need to browse to it and select it now using the “+” button.

2. Enter your base station information in the lower section and verify it is correct.  

• • • • Use Computed using Trimble CenterPoint RTX to compute the base station location from the submitted base station file to obtain a coordinate for that survey nail/reference mark. 
      • Use the Survey Nail Manager in the Base Station Location section middle of the dialog to Save your base station definition for future reference.  You can use the dropdown section to recall previously saved Survey Nail locations.

3. Click Next.

Ephemeris Settings Page

LP360 will only present the Ephemeris Settings page when required for the underlying GNSS post processing engine in use for the sensor being processed. The Ephemeris Settings page is used to configure the download of ephemeris or alternative navigation files, as well as configure additional GNSS processing settings. LP360 will attempt to download the necessary ephemeris files when the download button is pressed by the user or during the processing of the submitted PPT job.

• Ephemeris Mode:
  • Post-Processed (Downloaded from Internet) – Downloads the available mixed or GPS only ephemeris, and daily broadcast navigation file from the internet.
  • Broadcast (Use Alternate Navigation File (i.e., *.25N), downloaded from the Base Station (No internet connection required) – Uses the base station broadcast navigation file. No internet connection required.

• Ephemeris Files
  • Select to process using All Constellations (default) or to process using GPS only. You may elect to use GPS only if you are having issues processing a successful solution as one of the other constellations may be causing issues. Toggling this selection will trigger Auto-Download to download the corresponding ephemeris files.
  • Displays and allows for browsing to the ephemeris (.sp3) and/or the alternative navigation file (*.25N, *_GN.rnx for GPS Only, or *.25P, *_MN.rnx for All constellations).
  • Alternatively, manually download ephemeris files from the listed FTP links:
    1. Ephemeris FTP Server
    2. Ephemeris FTP Server (Mixed)
    3. Broadcast FTP Server (Daily)
  • The auto-download of the ephemerides is done via a connection to gdc.cddis.eosdis.nasa.gov (198.118.242.43) on port 21 using FTP-SSL. Your organization may only have a limited port range open and available for use by the auto-download function causing the auto-download to fail. You can use the Auto-Download Ephemeris Port Settings to limit the port range used by the FTP-SSL secondary data channel to auto-download ephemeris using only TCP ports within the specified range instead of the default, which is to use any port in the 1023-65535 range. A less accurate alternative, but possibly suitable for your needs, process using the Broadcast Mode and provide the *.25N or *_GN.rnx (GPS Only) or *.25P or *_MN.rnx (All constellations) file from your base station.
• GNSS Processing Settings
  • Elevation Mask (deg) and SNR Mask (dB) - The elevation mask and/or SNR mask can be changed by selecting the drop-down menu. The elevation mask is used to filter satellites low on the horizon, which can cause interference and reduced accuracy. Usually, it is best to start with the elevation mask set at 15, and then raise or lower it, as necessary. Getting all Q1 is the correct result. This means that there is fixed (2cm or less) accuracy. If there are Q2 or Q5 sections of the trajectory solution, then it may be necessary to check for missing/incorrect files or adjust the elevation mask and reprocess. For more information regarding GNSS quality levels, see GNSS Quality Levels Explained.
• Convert Base Observation File to RINEX 3.0 – This option can be used to convert your base station to the preferred RINEX 3.0 format. We do not have a good handle on when that is necessary. We have found it to be a viable solution in one instance if you cannot get a fixed solution (Q1) and are only achieving a float solution (Q2), yet everything looks like it should be achieving a fixed solution. However, we have also seen the opposite, where it was necessary to process without doing this conversion of the base station to get a fixed solution. We do not have a definitive answer yet as to when one or the other should be used.

Review / Results Page

1. You can review batch processing job estimates. When you are satisfied, select Submit to submit your Post Process Trajectory (PPT) job to the Job Manager .

2. The session will complete and ask you if you want to review the Post Process Trajectory Report and/or the Post Process Trajectory Plot , depending on the GNSS post processing engine used. This can be useful as a rapid check on the results.  The Position Errors RMS section of the report can provide an accuracy assessment.  The final Export Summary page can verify the output reference frame was set correctly for your project.

3. Click Close to dismiss the dialog.

Note: Note that running a post process trajectory (PPT) job does not create any new layers in your project. If you need to externally check that the output was created and added to your project data set, you can browse to the Cycle\POS folder of your project and verify a PostProcessedTraj.txt file was written here. There will also be a new subfolder named POSPac_yymmdd_tttttt for each job you run. These subfolders contain detailed logs and files related to trajectory processing and are useful for troubleshooting issues.