Editing LAS files

[Jan Depner]

I'm not sure if anyone on this list will be interested but, thanks
to Martin's LASlib and a v1.3 sample file with waveforms from Dan
Clewley (ARSF, NERC, UK), I have been able to add quite a bit of LAS
support to the Pure File Magic Area-Based Editor (PFMABE) suite of
software. The PFMABE software suite is all Open Source (mostly public
domain) and free (as in beer *and* as in speech). This is the same
software that is being used by the Army Corps of Engineers and the Naval
Oceanographic Office at the Joint Airborne Lidar Bathymetry Technical
Center of Expertise (JALBTCX). It can be downloaded from
http://pfmabe.software

I have modified the 3D point cloud editor (pfmEdit3D) and the 3D,
single file, along-track editor (fileEdit3D) to be able to
automatically, graphically display the waveform associated with the
nearest point as you move the cursor around in the point cloud. I've
posted an 8 minute video on our website (http://pfmabe.software)
demonstrating this and a few other capabilities. The waveform relevant
section starts at about 4:40 but the video up to that point is a short
tutorial on how to load LAS data into PFM. The waveform monitor is just
a proof of concept to show that we can instantly access the point data
and waveform data from any LAS point in the editor.

In addition to the waveform monitor I've added the ability to save
edits to the LAS files using the "withheld" bit. This can be done
either from a PFM built from LAS data (using pfm_unload) or directly
from within fileEdit3D. I wrote a few little C++ functions to provide
the ability to directly read and update specific records in a LAS file
but, other than that, I'm using LASlib for all I/O.

Right now I have no way to test how it handles "endian-ness" in the
C++ update code even though I've written the code to try to deal with
it. I haven't had my hands on a big-endian machine in about 20 years.
I also haven't provided support for external waveform files. If anyone
can direct me to a v1.3 or v1.4 LAS sample data set with external
waveforms I'll try to add that capability as well.


Cheers,
Jan

[Martin Isenburg]

Hello,

great stuff. Thanks for sharing.

One quick comment on internal storage of waveforms: Don't do it!

I discourage all my clients from exporting LAS 1.3 / 1.4 FWF files with internal storage. This has several disadvantages as every operation of the discrete LiDAR points that is written to a new file will have to also have to copy the insanely large FWF part ... where nothing ever changes. Much easier to keep them separate and only for on the LAS file for everything discrete and only ever touch the FWF file if really needed.

It should be possible to do the seperation of the WPD (or was it WDP) part into a separate file with laszip. Look at these forum posts on how to do this.  

http://groups.google.com/d/topic/lastools/bBLdL6-j1uY/discussion

http://groups.google.com/d/topic/pulsewaves/vWQuBsLFs0g/discussion

For follow-up discussions on LAS 1.3 / 1.4 FWF stuff also consider this group: http://pulsewaves.org

Regards,

Martin

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[Jan Depner]

I already sent this once but I used the wrong email address so here it
is again ;-)


Thanks for the links Martin. I just split the file with laszip. I
couldn't agree more about keeping the waveforms separate. I'll get to
work right away on supporting the external waveform files.

Also, I saw your post on GPS seconds of the week. I hope I never see
GPS seconds of the week again ;-) I remember sitting around at work in
August of 1999 waiting for the GPS week epoch to roll over so we could
see what was going to break on our ships (luckily nothing). But that
was just a wake-up call about fully time-tagging every data point.

Cheers,
Jan