LASzip lossless compression of LiDAR...LASzip fusa.laz R07205352.laz MARS_Sample.las autzen.las...

LASzip

lossless compression of LiDAR

Martin Isenburg

http://lastools.org

http://laszip.org

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

Simple LiDAR format: ASCII # x y z intensity

#

#

632441.315916 5241371.511566 297.164155 134

632441.489538 5241371.138985 297.384893 232

632440.711040 5241371.641106 297.404111 65

632438.872603 5241371.507230 298.037727 211

632439.354545 5241371.245455 300.450547 34

632439.619802 5241371.101926 302.021196 55

632440.637407 5241370.403773 301.072372 76

632441.223543 5241370.042336 301.439231 92

632441.285229 5241369.728593 301.298858 172

632440.519973 5241370.171933 301.733190 147

632439.612858 5241370.851281 302.580127 125

632439.340006 5241370.904065 300.062403 190

632438.620724 5241371.322045 299.246201 202

632438.260363 5241371.566035 298.630602 182

632436.544357 5241371.554476 302.572440 293

632437.604495 5241370.690458 300.955040 71

632438.223774 5241370.272349 301.742230 90

632438.920859 5241369.552097 297.597205 49

632438.829124 5241369.922948 302.242295 95

632439.382447 5241369.648279 303.473824 152

632440.346959 5241368.654692 298.592465 108

632439.672510 5241369.617202 305.104726 219

632440.379697 5241369.197974 305.976798 83

...

LiDAR points

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

The LAS & LAZ format

http://lasformat.org

http://laszip.org

LAStools

• started in January 2007 – API to read/write LAS

– lasinfo

– lasview

– las2txt

– txt2las

– laszip

• online since April 2007

• NEW: ArcGIS toolbox for LiDAR

http://lastools.org

Working with LAStools

run

Some Statistics

• LAStools user group: 830 members http://groups.google.com/group/lastools

• follow LAStools on facebook http://facebook.com/lastools

• follow LAStools on twitter http://twitter.com/lastools

• downloads

– in 2012: 2,991 (unique IPs)

– lifetime: 11,845 (unique IPs)

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

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

Compressing ...

• real stuff

– sleeping bags

– oxygen

• LiDAR points

– WinZIP, WinRAR, 7zip

– LizardTech® LiDAR

Compressor™ ($2995.00)

– LASzip ($0.00)

Predictive Compression

coordinate = 343,233

prediction = 343,214

corrector = coordinate - prediction

= 343,233 - 343,214

= 19 0

10

20

30

40

50

60

70

coordinate distribution

0

500

1000

1500

2000

2500

3000

3500

corrector distribution

x-axis 343,233 343,214

prediction

corrector

Entropy Coding

for a symbol sequence of t types

# of type t pi =

i = 1

t

Entropy = pi • log2( ) bits pi

1

# total

2.0 bits 1.3 bits 0.2 bits

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

LASzip fusa.laz R07205352.laz MARS_Sample.las autzen.las lincoln.las

• write header (uncompressed)

• write points in “chunks” of 50,000

– store first point raw (uncompressed)

– 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

search for “LASzip” on

http://youtube.com

Spatial Queries & “chunking”

spatial demo

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

Smorgasbord of 27 files

LAZ

388

MB

15.6

%

LAS

2,479

MB

SID

610

MB

24.6

%

RAR

551

MB

22.2

%

ZIP

1,210

MB

48.8

%

DNR Minnesota LiDAR

ftp://lidar.dnr.state.mn.us

LASzip vs. LizardTech® (1)

LAS

1,534

MB

LAZ SID

138 MB

9.0

% 388

MB

25.3

%

LAZ SID

3.3 times

slower

decode

LAZ SID

20.6 times

slower

encode

LASzip vs. LizardTech® (2)

LAS

2,454

MB

LAZ SID

407

MB

16

.6 %

716

MB

29.2

%

LAZ SID

4.6 times

slower

decode

LAZ SID

16.4 times

slower

encode

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

Demo: laszip.exe

run

Overview

• Preliminaries

• Compression

• The LASzip compressor

• Performance Results

• Live Demo

• Discussion

• fastest encoding / decoding

• highest compression

• tested across TB of data

• integrates with LAX spatial indexing

• open source

• LGPL-licensed

LASzip

• LAZ = lossless compressed LAS

http://laszip.org

FREE !!!

Downloading LAZ

• Open

Topography

• Minnesota

DNR

• NOAA

• USGS

• Dielmo

• …

Software support for LAZ

• TopoDot (Certainty 3D)

• FME 2012 (Safe Software)

• Global Mapper (BlueMarbleGeo)

• RiProcess (Riegl)

• LAStools

• Voyager 1.3.1 (Voyager GIS)

• ...

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

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

Thank You.

http://lastools.org

http://laszip.org

DNR Minnesota LiDAR (1)

ftp://lidar.dnr.state.mn.us

Detailed Results