Processing Full Waveform LiDAR data
There are still not many tools capable of full utilising the additional information present in full waveform data, for a list of software we are using / aware of see our Links page.
Some useful commands using our LAS 1.3 extraction script, LAStools and some other packages are listed below.
ARSF full waveform extraction tool
python fwf_extract.py LDR-FW-FW10_02-201010101.LAS
Requests user to input on command line the limits of area to extract and saves full waveform data to current directory
python fwf_extract.py LDR-FW-FW10_02-201010101.LAS -o /lidar/extraction
Requests user to input on command line the limits of area to extract and saves full wavefrom data to /lidar/extraction
python fwf_extract.py LDR-FW-FW10_02-201010101.LAS -o /lidar/extraction --area 560002 560000 318002 318000
Extracts wavefrom data for area bound by 560002 560000 318002 318000 to /lidar/extraction
python fwf_extract.py LDR-FW-FW10_02-201010101.LAS --header
Prints the Header of the LAS file to the screen and exits
NOTE: You need to have Python installed on your computer and to add the directroy of your Python distribution to your PATH environment variable.
See the Python user guide for more information: http://docs.python.org/using/windows.html#excursus-setting-environment-variables
Below are some useful commands for extracting the waveform from the LAS1.3 files.
To download the tools and for more information and help see http://www.cs.unc.edu/~isenburg/lastools/
las2txt -i LDR-FW-GB12_06-2012-083b-01.LAS -parse MrnxyzWV -o LDR-FW-GB12_06-2012-083b-01.txt
converts the LAS file LDR-FW-GB12_06-2012-083b-01.LAS to ASCII text using format MrnxyzWV
las2txt -i LDR-FW-GB12_06-2012-083b-01.LAS -parse MrnxyzWV -keep_wavepacket 1 -o LDR-FW-GB12_06-2012-083b-01.txt`
converts the LAS file LDR-FW-GB12_06-2012-083b-01.LAS to ASCII text using format MrnxyzWV keeping only those points containing waveform information
laszip -i LDR-FW-GB12_06-2012-083b-01.LAS -waveform
compresses the LAS file LDR-FW-GB12_06-2012-083b-01.LAS creating two compressed files
- LDR-FW-GB12_06-2012-083b-01.laz - containing the compressed discrete data and wave packet information
- LDR-FW-GB12_06-2012-083b-01.wpz - containing the compressed wave packet data
laszip -i LDR-FW-GB12_06-2012-083b-01.laz -waveform
decomressses the laz file LDR-FW-GB12_06-2012-083b-01.laz creating two file
- LDR-FW-GB12_06-2012-083b-01.las - containing the discrete data and wave packet information
- LDR-FW-GB12_06-2012-083b-01.wpd - containing the wave packet data
lasclip -i LDR-FW-GB12_06-2012-083b-01.laz -poly clip.shp -o LDR-FW-GB12_06-2012-083b-01_clip.laz`
subsets the laz file LDR-FW-GB12_06-2012-083b-01.laz using the polygon contained in clip.shp and ouputs the result to LDR-FW-GB12_06-2012-083b-01_clip.laz. Note this will only subset the laz file - the wpz file will still contain all points.
If you wish to extract the waveform data for a particular area bounded by 407049 200380 407067 200398 the workflow would be as follows:
laszip -i LDR-FW-GB12_06-2012-083b-01.LAS -waveform laszip -i LDR-FW-GB12_06-2012-083b-01.laz -waveform las2txt -i LDR-FW-GB12_06-2012-083b-01.las -clip 407049 200380 407067 200398 -parse MrnxyzWV -o LDR-FW-GB12_06-2012-083b-01_bounding_box.txt
If you wish to extract the waveform data for a particular area conatined in clip.shp the workflow would be as follows:
laszip -i LDR-FW-GB12_06-2012-083b-01.LAS -waveform laszip -i LDR-FW-GB12_06-2012-083b-01.laz -waveform lasclip -i LDR-FW-GB12_06-2012-083b-01.las -poly clip.shp -o LDR-FW-GB12_06-2012-083b-01_clip.las rename LDR-FW-GB12_06-2012-083b-01.wpd to LDR-FW-GB12_06-2012-083b-01_clip.wpd las2txt -i LDR-FW-GB12_06-2012-083b-01_clip.las -parse MrnxyzWV -o LDR-FW-GB12_06-2012-083b-01_clip.txt
In order to view the full waveform data you first need to create trajectory files. With the RawLaser data loaded in ALSPP select Utilities > Generate trj files. This creates an individual trajectory file for each flightline.
In TerraScan, select Manage Trajectories ( / icon) from the General tool bar. Under File > Set Directory select the location of the trj files.
Alternatively you can use the .sol file. Under Manage Trajectories > File > Import Files > *.sol. This creates a .trj covering the entire project (which is included with the delivery).
Load in a full waveform .LAS files. It is advisable to create a small fence and only load points inside the fence as TerraScan can't seem to cope with entire flightlines.
From the main TerraScan window select Flightline > Deduce Using Time.
On the main TerraScan toolbox select View Waveform Data to open the waveform viewer (the sideways barchart icon, on the bottom right of the Main toolbar). Under Settings > Display Settings you can adjust how the wave is viewed by varying maximum value (x axis) or sample height (y axis).
These are ASCII files (one file per return) containing the full waveform information.
- Draw a fence around the area of interest
- Open the View Waveform Data window
- File > Save As Text
This tool can be used to create additional discrete points from the full waveform data. Use the ambient noise value to set the threshold for detecting peaks (on the waveform viewer under Settings > Display Settings).
- Draw a fence around the area of interest
- Select Extract Echoes from the waveform toolbar