LASZIP and LAS V1.4 and Full Wave Form

[Aicke Damrau]

Dear Martin,

 

can you please shortly explain the relation between LAS V1.4, WaveForm and LASZIP?

A client wants to have a full wave form 1.4 LAZ file. Is this possible?

 

Mit freundlichen Grüßen

 

Aicke Damrau

 

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[Martin Isenburg]

Hello Aicke,

Can you please shortly explain the relation between LAS V1.4, WaveForm and LASZIP?

Both LAS 1.3 and LAS 1.4 have (limited) support to store digitized waveform data. For LAS 1.3 these are point types 4 and 5 and LAS 1.4 adds point types 9 and 10 in addition. You can use LAS 1.4 with the old point types 4 and 5 in which case there is not much practical difference to LAS 1.3 (other than that you could store more than 4 billion returns in the file).

Neither of these point types 4, 5, 9,10 actually store the waveform data. They just store the info of where the waveform data is located in the other file (the WDP file) and how to attach it to the return. The new point types 9 and 10 offer two main differences. (1) They are a little "wider" meaning that they have more bits to store return counts, number of returns, scan angle, classifications, and an additional flag as well as a scanner channel attribute. (2) Point type 10 also offers 4 band R/G/B/NIR storage.

The digitized waveforms should - as before - be stored in an external WDP file. Nothing changes here. Note that the specification allows to store the returns (the LAS part) and the digitized waveforms (the WDP part) into one LAS file but we highly discourage this practice.

LASzip can compress the LAS file part of a LAS 1.3 and LAS 1.4 (via the compatibility mode [1] as well as via the new native extension [2] (but for the latter it's better to wait a few more months)). 

[1] http://rapidlasso.com/2014/10/06/rapidlasso-announces-laszip-compatibility-mode-for-las-1-4/

[2] http://rapidlasso.com/2017/02/13/prototype-for-native-las-1-4-extension-of-laszip-lidar-compressor-released/

LASzip can also compress the (typically much larger) WDP file given a few assumptions that most commonly hold via the '-waveforms' command line flag but I am not sure a lot of people are using this and the LASzip DLL / LASzip via libLAS / PDAL API that is used in other software packages does not support this. Also this only works when the LAS and the WDP files are in separate files as they will be compressed into LAZ and WDZ files.

http://rapidlasso.com/LASzip

http://lastools.org/download/laszip_README.txt

A client wants to have a full wave form 1.4 LAZ file. Is this possible?

So yes, this is possible and I would suggest to use (for the time being) the old point type 5 in your LAS 1.4 file (unless the client asked explicitly for the new point type). Then you can use the good old LASzip and compress the content as long as there are less than 4 billion returns per file. I suggest to deliver the digitized waveforms as uncompressed external WDP files. Maybe the client will never use those anyways (unless this is for a science / research project but they would have probably asked for PulseWaves instead). If folks really want to have digitized waveform output then they should consider the PulseWaves format instead that can be produced by RIEGL RiPROCESS and by Optech LMS 3.0. I think Leica/AHAB are still only planning PulseWaves support and I beliebe Trimble's software can only give you LAS 1.3/1.4 FWF.

Maybe the client just wants "waveform-enhanced" discrete return data? Namely, the additional returns that the analogue hardware in a Leica or Optech scanner is not able to identify (due to the spacing or the number of the returns of one shot) but that can be found via post-processing the simultaneous digitized waveform? Of course, if you are flying a Q-line RIEGL then there is no analogue hardware and all your returns are found this way. But a lot of people seem to already call this "finding of additional returns" waveform LiDAR and don't actually expect the digitized waveform.

Regards,

Martin