LAS format

Susana Gonzalez

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Sep 10, 2016, 2:43:10 AM9/10/16

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Hi all,

I have a new set of tiles in the following format (attached example):

· version major.minor: 1.4

· point data format: 6

· point data record length: 30

I have started the process to normalise the data and then to compute the metrics without success.

My general script usually works with data in this format

· version major.minor: 1.4

· point data format: 1

· point data record length: 28

· Scanner channel in the User Data field

I have run this line of code

C:\LAStools\bin\las2las.exe -i C:\Analysis\Example.laz -set_version 1.4 -set_point_type 1 -odir C:\Outputs -olaz -cores 7

But I have the feeling that I lost some information…

Any help will be great.

Thanks

Susana Gonzalez - Forest Engineer, LiDAR Science

Interpine Group Ltd

DDI: +64 7 350 3209 or Australia 0280113645 ext 722
Skype: sugonar

Address : 99 Sala Street, PO Box 1209, Rotorua 3010, New Zealand
Website : www.interpine.co.nz

Interpine Innovation is Shaping Today’s Forests with the Technology of Tomorrow

He rangahau tenei ra he hangarau apopo

Example.zip

Martin Isenburg

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Sep 12, 2016, 8:16:51 AM9/12/16

to LAStools - efficient command line tools for LIDAR processing

Hello,

in the meantime Susana has sent me a full tile of LAS 1.4 data for closer inspection. There was one question and one problem:

==================

QUESTION:

Does this LAS 1.4 data with point type 6 contain any information that I will loose if I convert it to LAS 1.2 with point type 1.

ANSWER:

Your data seems to simply be "up-converted" LAS 1.2 data. As far as I can tell nothing will be lost.

==================

PROBLEM:

My script cannot run with these LAS 1.4 files that use point type 6 as input.

SOLUTION:

Option 1: Convert the LAS 1.4 files down to LAS 1.2 (and maybe compress at the same time) with:

las2las -i las14\*.las -set_version 1.2 -set_point_type 2 -odir las12 -olaz

Option 2: Use laszip to convert LAS 1.4 to LAZ 1.2 via the (current) default "compatibility mode":

laszip -i las14\*.las -odir las12 -olaz

Then proceed with the LAZ files as input as usual.

==================

Some more info. The main difference between point type 6 and point type 1 is illustrated in the attached image. None of those changes makes a difference for Susana's data because her data (also see the lasinfo report at the end of this message):

* has no more 7 returns per pulse (all are between 1 and 4)

* does not use the overlap flag

* does not use classification codes above 31 (all are between 1 and 18)

* does not use the scanner channel (the field is always 0)

* does not make use of the increased scanner channel resolution (while all scan angles are stored with a resolution of 0.006 thay are all rounded to the nearest full degree as the histogram shows)

Hence ... Susana really one has LAS 1.2 data to start with. I bet it was simply upconverted from LAS 1.2 point type 1 to LAS 1.4 point type 6. Why? Not sure. It's just a waste of two bytes per point as point type 6 is two (unused) bytes larger than point type 1. My advise would have been to use point type 1 in the first place. I believe we will see a lot of such "up-converted" data in the future as more and more folks are required to deliver LAS 1.4 point type 6 as per tender document.

The lasinfo options '-histo scan_angle 0.006' and '-histo extended_scan_angle 1' as you can seen them below will be part of the next LAStools release so you can also check if your higher resolution scan angle field is your new LAS 1.4 points really has higher resolution or still just stores the scan angle rank.

Regards,

Martin @rapidlasso

==========================

E:\LAStools\bin>lasinfo DouglasDaly2016_C2_754500_8447000.LAS -histo scan_angle 0.006 -histo extended_scan_angle 1

lasinfo (160910) report for DouglasDaly2016_C2_754500_8447000.LAS

reporting all LAS header entries:

file signature: 'LASF'

file source ID: 0

global_encoding: 16

project ID GUID data 1-4: 00000000-0000-0000-0000-000000000000

version major.minor: 1.4

system identifier: ''

generating software: 'TerraScan'

file creation day/year: 245/2016

header size: 375

offset to point data: 1083

number var. length records: 1

point data format: 6

point data record length: 30

number of point records: 3651719

number of points by return: 2953641 635434 60810 1804 30

scale factor x y z: 0.01 0.01 0.01

offset x y z: 0 0 0

min x y z: 754500.00 8447000.00 107.05

max x y z: 754999.99 8447499.99 137.23

start of waveform data packet record: 0

start of first extended variable length record: 0

number of extended_variable length records: 0

extended number of point records: 3651719

extended number of points by return: 2953641 635434 60810 1804 30 0 0 0 0 0 0 0 0 0 0

variable length header record 1 of 1:

reserved 0

user ID 'LASF_Projection'

record ID 2112

length after header 654

description 'OGC WKT'

WKT OGC COORDINATE SYSTEM:

PROJCS["GDA94 / MGA zone 52",GEOGCS["GDA94",DATUM["Geocentric_Datum_of_Australia_1994",SPHEROID["GRS 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],T

OWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG","6283"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHO

RITY["EPSG","4283"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",1

29],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",10000000],AUTHORITY["EPSG","28352"],AXIS["Easting",EAST],AXIS[

"Northing",NORTH]]

reporting minimum and maximum for all LAS point record entries ...

X 75450000 75499999

Y 844700000 844749999

Z 10705 13723

intensity 3 3266

return_number 1 5

number_of_returns 1 5

edge_of_flight_line 0 1

scan_direction_flag 1 1

classification 1 18

scan_angle_rank -30 30

user_data 0 0

point_source_ID 1 1

gps_time 86126.080314 88276.023324

extended_return_number 1 5

extended_number_of_returns 1 5

extended_classification 1 18

extended_scan_angle -4999 5000

extended_scanner_channel 0 0

number of first returns: 2953641

number of intermediate returns: 62687

number of last returns: 2953160

number of single returns: 2317769

WARNING: point type is 6 but (legacy) number of point records in header is 3651719 instead zero.

WARNING: point type is 6 but (legacy) number of points by return [1] in header is 2953641 instead zero.

WARNING: point type is 6 but (legacy) number of points by return [2] in header is 635434 instead zero.

WARNING: point type is 6 but (legacy) number of points by return [3] in header is 60810 instead zero.

WARNING: point type is 6 but (legacy) number of points by return [4] in header is 1804 instead zero.

WARNING: point type is 6 but (legacy) number of points by return [5] in header is 30 instead zero.

overview over extended number of returns of given pulse: 2317769 1149597 177098 7105 150 0 0 0 0 0 0 0 0 0 0

histogram of classification of points:

483 unclassified (1)

770281 ground (2)

1971412 low vegetation (3)

55359 medium vegetation (4)

854170 high vegetation (5)

5 noise (7)

9 Reserved for ASPRS Definition (18)

scan angle histogram with bin size 0.006

bin [-30,-29.994) has 16261

bin [-28.002,-27.996) has 36715

bin [-27,-26.994) has 78187

bin [-25.002,-24.996) has 40703

bin [-24,-23.994) has 119879

bin [-22.002,-21.996) has 82237

bin [-21,-20.994) has 161161

bin [-19.002,-18.996) has 78374

bin [-18,-17.994) has 158368

bin [-16.002,-15.996) has 77491

bin [-15,-14.994) has 156052

bin [-13.002,-12.996) has 77983

bin [-12,-11.994) has 135019

bin [-10.002,-9.996) has 45949

bin [-9,-8.994) has 82236

bin [-7.002,-6.996) has 39225

bin [-6,-5.994) has 77277

bin [-4.002,-3.996) has 38213

bin [-3,-2.994) has 79209

bin [-1.002,-0.996) has 40017

bin [0,0.006) has 198097

bin [1.002,1.008) has 83378

bin [3,3.006) has 162925

bin [4.002,4.008) has 78402

bin [6,6.006) has 158918

bin [7.002,7.008) has 78384

bin [9,9.006) has 154428

bin [10.002,10.008) has 76301

bin [12,12.006) has 153962

bin [13.002,13.008) has 67367

bin [15,15.006) has 103249

bin [16.002,16.008) has 38321

bin [18,18.006) has 76850

bin [19.002,19.008) has 38001

bin [21,21.006) has 77410

bin [22.002,22.008) has 38324

bin [24,24.006) has 112902

bin [25.002,25.008) has 77848

bin [27,27.006) has 155025

bin [28.002,28.008) has 74366

bin [30,30.006) has 26705

average scan angle 0.0265653 for 3651719 element(s)

extended scan angle histogram with bin size 1

bin -4999 has 16261

bin -4666 has 36715

bin -4499 has 78187

bin -4166 has 40703

bin -3999 has 119879

bin -3666 has 82237

bin -3499 has 161161

bin -3166 has 78374

bin -2999 has 158368

bin -2666 has 77491

bin -2499 has 156052

bin -2166 has 77983

bin -1999 has 135019

bin -1666 has 45949

bin -1499 has 82236

bin -1166 has 39225

bin -999 has 77277

bin -666 has 38213

bin -499 has 79209

bin -166 has 40017

bin 0 has 198097

bin 167 has 83378

bin 500 has 162925

bin 667 has 78402

bin 1000 has 158918

bin 1167 has 78384

bin 1500 has 154428

bin 1667 has 76301

bin 2000 has 153962

bin 2167 has 67367

bin 2500 has 103249

bin 2667 has 38321

bin 3000 has 76850

bin 3167 has 38001

bin 3500 has 77410

bin 3667 has 38324

bin 4000 has 112902

bin 4167 has 77848

bin 4500 has 155025

bin 4667 has 74366

bin 5000 has 26705

average extended scan angle 4.42755 for 3651719 element(s)

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LAS14_point_type_6.png

Susana Gonzalez

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Sep 14, 2016, 4:35:42 AM9/14/16

to last...@googlegroups.com, David Herries

Hi Martin,

Thank you so much for your support, from now on we will be more careful of what we request to the provider and be sure that they can provide our request without doing “up-conversion”.

Cheers

Susana

Susana Gonzalez Interpine Group Ltd

DDI: +64 7 350 3209 or Australia 0280113645 ext 722

Interpine Innovation is Shaping Today’s Forests with the Technology of Tomorrow

He rangahau tenei ra he hangarau apopo

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