Airborne Laser Scanner (ALS) processing

General Processing with a settings (.reg) file

1. Start ALS PP (possibly using Linux)
2. Load in the reg file to set the specific settings for the project.
   • Reg files under ~arsf/calibration/lidar, pick the date before the flight you're processing
   • File > Load Settings
3. For Wine, Go to Inputs > Range Correction and for Intensity Based Range Correction browse to \users\rsg\arsf\calibration\lidar\... and select the relevant SN089_IBRC*txt file for the flight day you are processing
4. Set the Goto Folder to the main project directory
   • File > Set Goto Folder
5. Check the settings are appropriate for the project before proceeding (see below). This is important if using a reg file for a different project.
6. Add the raw SCN data
   • Click Add and browse to the parent raw data directory. This will add all flight lines in the immediate child directories.
7. Select POS filename
   • Click Browse and add the .sol file
8. Select the Output directory
   • Click Select > Goto Folder and select <projname>/leica/proc_laser. You should create directory if it doesn't exist.
9. If you have large flightlines, limit the .LAS files to 10 million points (under file, output options) to make it easier to classify the points in TerraScan
10. If the project is not in the UK, you will need to change the projection (File -> Output Options -> Change output format)
11. Save settings for future re-processing purposes.
    • File > Save Settings (e.g. aux_files/2009280b.reg)
12. Run the processing
    • Run > Run

Setup of the system

• Hardware options. Once set these should never change (unless the system is modified etc) Should be supplied when the system is delivered. Can view/set these from File > Processing Options.
• Output file options. Set the projection details (usually OSGB36), LAS file format, and whether want GeoTIFF or ASCII output awswell. Also contains options for debugging.

• Input options
  • Atmospheric Correction. Need values of the altitude, temperature and pressure for a low altitude and high altitude. With these values a correction gradient will be produced.
  • Range Correction. A time-distance delay in metres of the ALS system, in the measurement of range data. (This is complicated...see user manual for details)
  • Scanner Correction. These do not need to be changed after the calibration/boresighting of the system.
  • POS errors. Angular difference between the IMU and the ALS optics reference frames. Needs to be known accurately.
  • Elevation offset. This needs to be set if we have ground control points: is normally non-zero. It is identified using the TScan Control Report (eh?). The LIDAR is then reprocessed using the opposite of the DZ offset.
  • Intenisty. Use the Raw intensity.

Possible errors

• ALSPP.EXE on Linux

1. If a Windows crash message appears when trying to 'Run', ensure the POS file is pointed to on the Linux filesystem and not the Windows hard drives (D:,.. etc.).