LASzip Chunk Table Issue

[Mustafa Agah Öztürk]

Hello,

As far as I understood from the specification, every LASzip file has to be chunked, no matter how big the chunks are, the default value is 50000. After the VLR records, there is a chunk table which tells you the location of every chunk in the file.

I received a LASzip file which doesn't seem have a chunk table, there is a weird value in the position where I'm used to read the chunk positions. Unfortunately I can't share the data with you, but I wonder whether it's possible. Lasview can visualize the data somehow, but the data doesn't seem valid according to the spec.

lasinfo output :

reporting all LAS header entries:

  file signature:             'LASF'

  file source ID:             0

  global_encoding:            0

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

  version major.minor:        1.2

  system identifier:          'LAStools (c) by Martin Isenburg'

  generating software:        'PTS by pointzip 1.0 (120723)'

  file creation day/year:     149/2018

  header size:                227

  offset to point data:       313

  number var. length records: 1

  point data format:          2

  point data record length:   26

  number of point records:    761336647

  number of points by return: 761336647 0 0 0 0

  scale factor x y z:         0.001 0.001 0.001

  offset x y z:               0 0 0

  min x y z:                  -35.386 -34.795 -3.330

  max x y z:                  18.702 38.892 3.899

variable length header record 1 of 1:

  reserved             43707

  user ID              'LAStools'

  record ID            2000

  length after header  32

  description          'by LAStools of Martin Isenburg'

LASzip compression (version 2.1r0 c2 50000): POINT10 2 RGB12 2

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

Kind regards.

[Martin Isenburg]

Hello,

this can happen when the compression process is killed/cancelled/fails/aborts during compression before the compressor had a chance to write the "chunk table". In this case a special (or weird) value is written into the field that usually stores the start position of the chunk table. Hence when an interruption occurs then you can only read the file sequentially (without chunk table) until the moment it was truncated. In that case the last few points can be corrupt. Run:

laszip -i in.laz -check

to verify and

las2las -i orig.laz -o recovered.laz

to recover as many points as possible and create a new chunk table. Maybe look with

lasinfo -i orig.laz -report_outside

whether corrupt points at the very end of the file are now outside the bounding box.

Regards,

Martin @rapidlasso

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