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

[Martin Isenburg]

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.

Regards from Brazil,

Martin @rapidlasso

On Wed, Nov 9, 2016 at 9:12 PM, Van Dyke, Daryl <daryl_van_dyke at fws.gov>
wrote:

> LAStools IIRC encodes the non-standard HAG field into the 'user bytes'
> portion of the LAS file.  It's special-sauce approach to encoding that
> information into a user-expandable portion of the LAS standard.
>
> To keep in mind: the HAG field (again, IIRC) is based on an internal
> integer representation - it quantizes the data into the binned integers to
> store them.  You want to ensure the resolution of the storage is
> appropriate for your application (though for most tree sizes, in most
> units, it's probably fine).
>
> I don't think you'll find any tools outside of LASTools that support that
> feature.  You may also not be aware that the 'free' or non-licensed version
> of LASTools imposes noise on output.
>
> Daryl
>
> On Wed, Nov 9, 2016 at 12:00 PM, <liblas-devel-request at lists.osgeo.org>
> wrote:
>
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>> Today's Topics:
>>
>>    1. libLAS and HEIGHT_ABOVE_GROUND attribute (Alexandre Guyot)
>>
>>
>> ---------- Forwarded message ----------
>> From: Alexandre Guyot <alexguyot at yahoo.fr>
>> To: "liblas-devel at lists.osgeo.org" <liblas-devel at lists.osgeo.org>
>> Cc:
>> Date: Tue, 8 Nov 2016 21:00:17 +0000
>> Subject: [Liblas-devel] libLAS and HEIGHT_ABOVE_GROUND attribute
>> Hi,
>>
>> I'm using the liblas python API to read through some LiDAR point clouds.
>> I can access all the standard point attributes of my dataset, however I
>> can't figure out how to read the HEIGHT_ABOVE_GROUND value of my points.
>> This HEIGHT_ABOVE_GROUND attribute was computed in LAStools using
>> "lasheight".
>> This attribute is readable on popular LiDAR viewers (GlobalMapper for
>> instance) but I don't know how to reach it using libLAS.
>>
>> Any ideas ?
>>
>> Thanks a lot,
>> Alex
>>
>>
>>
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>
>
>
> --
> _________________________________________
> Daryl Van Dyke
> GIS Analyst
> Klamath Strategic Habitat Conservation Team
> US Fish & Wildlife Service - AFWO, R8
> (707) 825-5153
> https://github.com/GeospatialDaryl
>
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