LASzip lossless compression of LiDAR

Transcription

1 LASzip lossless compression of LiDAR Martin Isenburg

2 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

3 Simple LiDAR format: ASCII # x y z intensity # # LiDAR points

4 LiDAR explodes airborne and mobile platforms scan with increasing detail impractical to store points as gigantic ASCII text files inefficient to parse, seek, write, ASPRS creates LAS(er) format binary LiDAR exchange standard

5 The LAS & LAZ format

6 LAStools started in January 2007 API to read/write LAS lasinfo lasview las2txt txt2las laszip online since April 2007 NEW: ArcGIS toolbox for LiDAR

7 Working with LAStools run

8 Some Statistics LAStools user group: 830 members follow LAStools on facebook follow LAStools on twitter downloads in 2012: 2,991 (unique IPs) lifetime: 11,845 (unique IPs)

9 Dual Licensing open source part LASlib (with LASzip) core tools: las2las, las2txt, laszip,... free (LGPL license) closed source part not free, except for academic or educational use (with point limits) full versions can be licensed

10 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

11 Compressing... real stuff sleeping bags oxygen LiDAR points WinZIP, WinRAR, 7zip LizardTech LiDAR Compressor ($ ) LASzip ($0.00)

12 Predictive Compression prediction corrector 343, ,233 x-axis coordinate distribution coordinate = 343, prediction = 343,214 corrector = = coordinate - prediction 1500 = 343, , corrector distribution

13 Entropy Coding for a symbol sequence of t types Entropy = t i = 1 1 p i log ( ) 2 bits p i p i = # of type t # total 0.2 bits 1.3 bits 2.0 bits

14 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

15 LASzip fusa.laz R laz MARS_Sample.las autzen.las lincoln.las write header (uncompressed) write points in chunks of 50,000 store first point raw (uncompressed) search for LASzip on compress next point predict attributes that have changed return number, intensity, scan angle, predict coordinates using Δx, Δy, z treat GPS time as integer, predict steps

16 Spatial Queries & chunking spatial demo

17 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

18 Smorgasbord of 27 files 48.8 % 1,210 MB 22.2 % 551 MB 24.6 % 610 MB 15.6 % 388 MB 2,479 MB ZIP RAR SID LAZ LAS

19 DNR Minnesota LiDAR ftp://lidar.dnr.state.mn.us

20 LASzip vs. LizardTech (1) 20.6 times slower 25.3 % 1,534 MB SID LAZ encode 3.3 times slower SID LAZ decode 388 MB SID 9.0 % 138 MB LAZ LAS

21 LASzip vs. LizardTech (2) 16.4 times slower SID LAZ 4.6 times slower SID LAZ 29.2 % 716 MB 16.6 % 407 MB 2,454 MB encode decode SID LAZ LAS

22 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

23 Demo: laszip.exe run

24 Overview Preliminaries Compression The LASzip compressor Performance Results Live Demo Discussion

25 LASzip LAZ = lossless compressed LAS fastest encoding / decoding highest compression tested across TB of data integrates with LAX spatial indexing open source LGPL-licensed FREE!!!

26 Downloading LAZ Open Topography Minnesota DNR NOAA USGS Dielmo

27 Software support for LAZ TopoDot (Certainty 3D) FME 2012 (Safe Software) Global Mapper (BlueMarbleGeo) RiProcess (Riegl) LAStools Voyager (Voyager GIS)...

28 Future Work faster encoding/decoding embarassingly parallel one chunk per thread LAS 1.4 correlate points along same pulse better extra bytes support integrate full waveform

29 Acknowledgements users of LAStools for bug reports Howard Butler for chunking Tim Loesch of DNR Minnesota for first large-scale LAZ campaign Dave Finnegan of USACE for financial support Michael P. Gerlek and Howard Butler for liblas integration help

30 Thank You.

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33 DNR Minnesota LiDAR (1) ftp://lidar.dnr.state.mn.us

34 Detailed Results