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I have a LASCatalog that is producing some funky outputs so I ran a lascheck() on it. The output tells me that catalog has inconsistent number of VLR, but what does this mean? I know that variable length records are part of the las file structure, but what problems could come from having an inconsistent number of them in my catalog?

Output from lascheck():

> lascheck(chunk2)

 Checking headers consistency
 - Checking file version consistency... ✓
 - Checking scale consistency... ✓
 - Checking offset consistency...
    ⚠ Inconsistent offsets
 - Checking point type consistency... ✓
 - Checking VLR consistency...
    ✗ Inconsistent number of VLR
 - Checking CRS consistency... ✓
 Checking the headers
 - Checking scale factor validity... ✓
 - Checking Point Data Format ID validity... ✓
 Checking preprocessing already done 
 - Checking negative outliers... ✓
 - Checking normalization... no
 Checking the geometry
 - Checking overlapping tiles... ✓
 - Checking point indexation... no

Some tiles have the following VLRs:

Variable length records: 
   Variable length record 1 of 3 
       Description: by LAStools of rapidlasso GmbH 
       Tags:
          Key 1024 value 1 
          Key 3072 value 26918 
          Key 3076 value 9001 
          Key 4099 value 9001 
   Variable length record 2 of 3 
       Description: NIIRS10 Tile Index 
   Variable length record 3 of 3 
       Description: NIIRS10 Timestamp 
       Extra Bytes Description:

While others only have:

Variable length records: 
   Variable length record 1 of 3 
       Description: by LAStools of rapidlasso GmbH 
       Tags:
          Key 1024 value 1 
          Key 3072 value 26918 
          Key 3076 value 9001 
          Key 4099 value 9001 

LASCatalog before processing:

enter image description here

LASCatalog after normalization showing strange results: enter image description here

Figure from spplot(chunk2_ctg, "Number.of.variable.length.records"): enter image description here

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  • Perhaps I should be worried about the inconsistent offsets as well? After further inspection I have also found inconsistent GPS time formats (standard time and week time).
    – Lucas
    Dec 9, 2019 at 15:59
  • Please show the figure generated by spplot(ctg, "Number.of.variable.length.records")
    – JRR
    Dec 9, 2019 at 18:19

1 Answer 1

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It depends on the VLRs. Honestly I have never encountered trouble with inconsistent catalog yet. My answer is theoretical. So, in theory...

Nothing serious can happens in general case. Here the catalog is inconsistent so the files may come from different providers with different densities, different sensors, different intensities, different CRS and so on. lascheck with a LAScatalog basically tells you "be careful, please ensure you are sure of what you are doing".

However it can be a problem if VLRs record some extra attributes in the files. Let say you have an additional attributes Amplitude that does not appear consistently in the files, the reading may crash (never tested actually).

If you have a "funky" output it probably comes from somewhere else. But you should clarify what "funky" means.

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  • I've edited my initial question to include the "funky" output.
    – Lucas
    Dec 9, 2019 at 14:33
  • You are in the 2nd case with extra attributes. My answer remains valid but please open an issue in the github repository. I don't have any clue to explain your output so we will try, at least, to handle this case nicely with informative errors.
    – JRR
    Dec 9, 2019 at 18:17
  • 1
    thanks for looking into this. I think the files may been corrupted during their download. I re-downloaded the files and I'm no longer seeing the "funky" outputs...
    – Lucas
    Dec 9, 2019 at 22:26

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