[Liblas-devel] Liblas-devel Digest, Vol 79, Issue 1

[Martin Isenburg]

Hi,

in this case you are indeed just be storing HAG as a quantized value in
decimeters (or decifeet) in the 8 bit unsigned user_data field that ranges
from 0 to 255 (e.g. 0 to 25.5 meters or feet). See the README file of
lasheight for details.

http://lastools.org/download/lasheight_README.txt

Furthermore you seem then to merely visualize the user_data field in Global
Mapper and not a dedicated HAG field.

Regards,

Martin

On Wed, Nov 9, 2016 at 9:55 PM, Alexandre Guyot <alexguyot at yahoo.fr> wrote:

> Hi,
>
> Thanks for your help.
> Actually, I havent' specified any switch in lasheight.
>
> My file is in LAS 1.2 and effectively has the HAG value as it can be read
> by some commercial software such as GlobalMapper (as "HEIGHT_ABOVE_GROUND"
> attribute).
>
> Is it therefore stored somewhere else than in extra-bytes or was LAS 1.2
> already using extra-bytes ?
>
> Thanks,
> Alex
>
>
>
>
> ------------------------------
> *De :* Howard Butler <howard at hobu.co>
> *À :* Martin Isenburg <martin.isenburg at gmail.com>
> *Cc :* "Van Dyke, Daryl" <daryl_van_dyke at fws.gov>; "
> Liblas-devel at lists.osgeo.org" <liblas-devel at lists.osgeo.org>
> *Envoyé le :* Mercredi 9 novembre 2016 21h29
> *Objet :* Re: [Liblas-devel] Liblas-devel Digest, Vol 79, Issue 1
>
>
> > On Nov 9, 2016, at 2:20 PM, Martin Isenburg <martin.isenburg at gmail.com>
> wrote:
> >
> > Hi,
> >
> > I believe that Alex talks about the HAG stored as an additional point
> atttribute to an "Extra Bytes" field via the '-store_as_extra_bytes' switch.
> >
> > http://lastools.org/download/lasheight_README.txt
> >
> > There was a discussion on this in the LAStools user forum whether cm
> resolution with a scale factor of 0.01 and a 16 bits signed integer storage
> are enough for most trees.
> >
> > http://groups.google.com/forum/#!searchin/lastools/
> lasheight$20store_as_extra_bytes
> >
> > "Extra Bytes" fields are described in the LAS 1.4 specification and are
> therefore also more and more readable in other software.
>
> All of this is accurate information.
>
> Additionally, libLAS does not support LAS 1.4 or support writing LAS 1.4
> extra bytes descriptor VLRs. You'll need to use LAStools or PDAL or LASpy
> to achieve this task if open source is a priority for you.
>
> Howard
>
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>
>
>
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