Version 39 (modified by dac, 10 years ago) (diff)

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Processing LIDAR data from Leica ALS50

This page describes the basic steps involved in processing the Raw Scan data from the Leica ALS50 II. More information can be found here

The first stage is to post-process the GNSS data and blend it with the IMU data to get the best position and altitude of the laser scanner for the flight. This uses the IPAS Pro and Grafnav software packages on windows.

Raw scan to point cloud

This stage of the processing takes the raw scanner files and georeferences them to create a point cloud of the data. This is usually in the binary LAS format but may be output as ASCII if you wish. This uses the ALSPP software, however it is recommended you use alsproc for roll and pitch corrections.

After running the ALSPP check the % of first returns column in the main window. This should be high (probably >95%). If not then it may be an indicator to problems with the data (such as a large % of cloud coverage)

Data QC

Full QC procedure.

The final stages of the processing are to quality check the data and filter out noisy points. This can be very time consuming. See tips on using Terrascan and also here for further notes from leica.

The main steps will be:

  • to re-classify noisy points (haze, low points and isolated points)
  • check the horizontal overlap between neighbouring lines
  • check the elevation overlap between neighbouring lines
  • check the data against OS vectors if available
  • if GCPs available then compare them against LIDAR

Once QC is complete, you need to start creating the delivery. Instructions are here.

Processing Full Waveform Data

If there is full waveform data with the project then follow the instructions below.

Once the discrete data has been processed, use the same .reg file (with the corrected roll value) to process the full waveform data.

Load the .reg file in ALSPP. Under Inputs> Waveform Processing check the box Process Waveform Data. Ensure the correct trigger delay values are entered - these should be populated from the calibrated reg file.

Load in the RawLaser data and select Run.

If you get an error "Unable to open the waveform file in selected folder" ensure that the raw data folders are in the correct structure - RawLaser & RawWFD (case sensitive). The full waveform files will be in the format *_4.LAS.

If the entire point cloud is mapped to x/y/z of 0 try importing only the line you are trying to process (the folder containing the scn files for this flight).

Once the data has been processed it can be viewed in TerraScan. Details on this can be found here

Run get_class_las to copy your classified points from discrete data into the fw data, this must be done before the delivery is created.

At the moment, there are no tools available to do any post-processing of the full waveform data.

Exporting AGC Values

By default the Automatic Gain Control Value (AGC) is not exported. If the PI intends to normalise or calibrate the intensity data the 'Output AGC in Flight Line ID field' in ALSPP output file options needs to be checked. This will store the AGC values in the Flight Line ID field and User field of the LAS file.

Calibration Files

The .reg files for the ALS processing can be found in the calibration directory of the ARSF repository in the lidar subdirectory. After a new calibration, write the details here and copy the new reg file to the arsf repository.

April 2015 day 96 - 2014_096_calibration.reg

August 2014 day 238 - 2014_238_calibration.reg Note: if you are using ALSPP to calculate the roll offsets you must use '2014_238_calibration_no_fla.reg'

July 2014 day 182 - 2014_182_calibration.reg Note: This calibration is to be used for data from day 141 onwards

March 2014 day 78 - 2014_078_calibration.reg

November 2013 day 308a - 2013_308a_calibration.reg

July 2013 day 192 - 2013_192_calibration.reg

February 2013 day 50 - 2013_050_calibration.reg

May 2012 day 125 - 2011_125_calibration.reg Note: This calibration is to be used for data from day 080 onwards

July 2011 day 195a - 2011_195a_calibration.reg
Note: This calibration is to be used for data from day 130 onwards

April 2011 day 109 - 2011_109_calibration.reg
Note: This is the calibration for the Loan System and relevant for data from day 092 - day 109 only

March 2011 day 082 - 2011_082_calibration.reg

April 2010 day 096 - 2010_096_calibration.reg

March 2010 day 060 - 2010_060_calibration.reg

September 2009 day 268 - 2009268_final.reg

September 2009 day 252 - 2009252a_calibration.reg

June 2009 day 180 - sn89_calibration_2009180a.reg

February 2009 day 058 - sn89_leica_calibrated_ammended_rangecorr.reg

December 2008 - SN089_Calibrated_by_Lecia-081206.reg

November 2008 - 20081101_calibration.reg