[pdal] Riegl extrabytes stripped

[Andrew Bell]

On Mon, Oct 3, 2016 at 6:28 AM, Kristian Evers <kreve at sdfe.dk> wrote:

> Hi.
>
>
>
> I have some laz-files that incoorporates Riegl’s extrabytes waveform
> extension [0]. I am running the files through a PDAL pipeline but
> unfortunately the VLR header and extrabytes are stripped from the resulting
> files. This behavior of writers.las is documented on the webpage [1]. The
> forward options description ends with:
>
>
>
> “VLRs can be forwarded by using the special value ‘vlr’. VLRs containing
> the following User IDs are NOT forwarded: ‘LASF_Projection’, ‘LASF_Spec’,
> ‘liblas’, ‘laszip encoded’. These VLRs are known to contain information
> regarding the formatting of the data and will be rebuilt properly in the
> output file as necessary. Unlike header values, VLRs from multiple input
> files are accumulated and each is written to the output file. Forwarded
> VLRs may contain duplicate User ID/Record ID pairs.”
>
>
>
> The Riegl extrabytes are stored with user ID “LASF_Spec” and record ID 4.
> I accept that it is necessary to treat some VLR’s differently than others,
> but I don’t think this is one of them.
>

The LASF_Spec is defined in the LAS 1.4 specification and needs special
handling by PDAL.  In order to support LAS 1.4, PDAL needs to write
arbitrary dimensions to the output as extra bytes and also needs to be able
to construct the LASF_Spec VLR to reflect the data in the extra bytes.

Without a sample data file, I really don't know what's going on or why the
data isn't being forwarded as expected.


> The extra-bytes in this case contains data that PDAL has no way of knowing
> how to reconstruct properly.
>

I don't believe this is true.  The VLR should describe the data on input,
which should allow it to also properly reconstructed on output.


> I believe something similar happens when storing waveform data as
> specified in LAS v. 1.3 since it is also defined as VLR’s with user ID
> “LASF_Spec” (and record ID in the interval 100-355).
>

Waveform data is explicitly not supported by PDAL (we don't support point
formats 4, 5, 9 and 10).

I would much prefer the extrabytes attached to each record just be
> forwarded like any other VLR and extrabytes data. A way to do this would be
> to only ignore VLRs with certain user ID’s that matches data that PDAL
> knows how to construct properly at write-time.
>

PDAL is handling formats other than LAS.  The current handling allows data
read from some other format to be properly written to a LAS 1.4 file, using
the LASF_Spec VLR and extra bytes to store data not supported by the native
LAS point formats.  In order to diagnose your issue, I need to examine the
data in more detail.

-- 
Andrew Bell
andrew.bell.ia at gmail.com
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