Add new VLR or Comment

[WickedGardener]

This is an issue related to: https://groups.google.com/g/lastools/c/Q7lQ7ChGmiE

I'd like to know if or how I could add my own custom VLR to a las file using LASTOOLS. Actually all I'd like to do is put a "comment" such as "this file contains data collected on 12 Dec 2020" or something similar. Can I do that? Do I even need to use a VLR?

I was thinking to use a VLR. For example:

variable length header record 2 of 2:
  reserved             0
  user ID              'Origin'
  record ID            101
  length after header  24
  description          'TopoDOT Scanner Origin'

but change user ID to "Collection date"

and description to "12 Dec 2020"

Thanks.

[Martin Isenburg]

Hello,

if you already have a VLR in place and you just want to change it's name or description you can use lasinfo with one of these options and do it in place:

-set_vlr_record_id 2 4711
-set_vlr_user_id 1 "hello martin"
-set_vlr_description 0 "hello martin"

http://rapidlasso.com/lasinfo  

if you need to add a new empty VLR you need to download this new version:of las2las:

https://www.dropbox.com/s/ere9wpz87rkirmx/las2las.exe

here you have this new option

-add_empty_vlr "hello martin" 4711 "i like laser chickens"  

http://rapidlasso.com/las2las 

Here an example run:

E:\software\LAStools\bin>las2las -i ..\data\fusa.laz -add_empty_vlr "hello martin" 4711 "i like laser chickens" -o fusa.laz

E:\software\LAStools\bin>lasinfo fusa.laz
lasinfo (201224) report for 'fusa.laz'
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:        1.1
  system identifier:          'LAStools (c) by rapidlasso GmbH'
  generating software:        'las2las (version 210114)'
  file creation day/year:     40/2010
  header size:                227
  offset to point data:       375
  number var. length records: 2
  point data format:          1
  point data record length:   28
  number of point records:    277573
  number of points by return: 263413 13879 281 0 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               0 0 0
  min x y z:                  277750.00 6122250.00 42.21
  max x y z:                  277999.99 6122499.99 64.35
variable length header record 1 of 2:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34735
  length after header  40
  description          'by LAStools of Martin Isenburg'
    GeoKeyDirectoryTag version 1.1.0 number of keys 4
      key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: ModelTypeProjected
      key 3072 tiff_tag_location 0 count 1 value_offset 32754 - ProjectedCSTypeGeoKey: WGS 84 / UTM 54S
      key 3076 tiff_tag_location 0 count 1 value_offset 9001 - ProjLinearUnitsGeoKey: Linear_Meter
      key 4099 tiff_tag_location 0 count 1 value_offset 9001 - VerticalUnitsGeoKey: Linear_Meter

variable length header record 2 of 2:
  reserved             0

  user ID              'hello martin'
  record ID            4711
  length after header  0
  description          'i like laser chickens'
LASzip compression (version 3.4r3 c2 50000): POINT10 2 GPSTIME11 2
reporting minimum and maximum for all LAS point record entries ...
  X            27775000   27799999
  Y           612225000  612249999
  Z                4221       6435
  intensity          10      62293
  return_number       1          3
  number_of_returns   1          3
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification      1          6
  scan_angle_rank    79        103
  user_data           0        197
  point_source_ID     1          1
  gps_time 5880.963028 5886.739738
number of first returns:        263413
number of intermediate returns: 283
number of last returns:         263370
number of single returns:       249493
overview over number of returns of given pulse: 249493 27232 848 0 0 0 0
histogram of classification of points:
           17553  unclassified (1)
          180868  ground (2)
           37030  high vegetation (5)
           42122  building (6)

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[Eric Putman]

This is a great new capability. Thanks, Martin.

[WickedGardener]

Thank you Martin. This works great. It looks like there is a limit on 31 characters to the "description" field. Is there a way to change this? Also, is there a good online spec for VLRs in general? I'm just now learning about them.

Thanks Again!

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[Eric Putman]

Hello Jochen,

I was wondering if this functionality could please be expanded to include the capability of adding a "non-empty" VLR?

With the current "-add_empty_vlr" call, it seems like the user can add a VLR with a customized user ID, record ID, and description, but this VLR is empty and it doesn't seem like there is a way to insert a VLR with an actual payload of data. As mentioned above, the "description" field is limited in length which makes it difficult to use for storing desired information in a VLR. I think there could be many reasons to do so, but my main use case at the moment would be to add more detailed datum descriptions for certain localized/custom geodetic networks that aren't described by "normal" EPSG codes or standard WKT strings. I can send an example file if that's helpful, but hopefully my description makes sense.

Thank you and long may LAZ reign!

R,

Eric

[Jochen Rapidlasso]

Hi Eric,

thanks for your suggestion. This is a good idea, to make the VLR handling more powerfull. We will put this on the todo-list.

Just as an idea: Right now you could use las2las64 with the argument -save_vlrs to extract VLRs to a file, you can patch this file and put it back using -load_vlrs.

First byte saved is the number of VLRs, then for each VLR you have to set the field "record_length_after_header" to the size of your binary data.

Please see the save_vlrs method to see the file structure in detail.

Best,

Jochen @rapidlasso