[GRASS-user] Lidar points height from ground

[Daniel Victoria]

Hi Daniel Lee (two Daniels changing emails is a hard thing to follow...)

I can create the different height classes raster easily but I'm not
sure how to get the lidar points from the cloud that are in each
vertical slice.

Maybe work with raster volumes? Is there a way to cross points at
different volumes?

The fact is, I'm not seeing how to do this without having to import
the lidar point cloud.

Schematically, what I want to do is count the number of points that
are in the vertical bins 1 2, (g is ground), a vertical slice...
         ___
         | . :
bin 2  | :
         | .
         -----
bin 1  | ...
         | .
        ggggg

Cheers and many thanks for the attention
Daniel V


On Fri, Mar 30, 2012 at 8:08 AM, Daniel Lee <lee at isi-solutions.org> wrote:
> Hi Daniel,
>
> You could try making different rasters with classes (0-5m over ground, 5-10m
> over ground, etc.) and then convert them into polygons, then check how many
> points are inside them. I'm not sure if it'd be faster than the way you
> suggested originally, though, when you think that you'd have to make the
> rasters first, etc.
>
> I ended up giving up on large vector operations with LiDAR point clouds in
> GRASS 6.4 because it simply took way too long, but I was dealing with
> millions of points. For such a small dataset it's probably fine, since as
> long as you know your script is okay you can let it run through your lunch
> break ;)
>
>
> Daniel
>
> --
>
> B.Sc. Daniel Lee
> Geschäftsführung für Forschung und Entwicklung
> ISIS - International Solar Information Solutions GbR
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>
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>
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>
>
> Am 30. März 2012 13:00 schrieb Daniel Victoria <daniel.victoria at gmail.com>:
>
>> I need to calculate the number of points at different height levels. That
>> is, how many points are from 0 to 5 meters? And from 5 to 10? And so on. So
>> I believe I need to work with vector points and a database. Or is there
>> another way?
>> Thanks
>> Daniel
>>
>> On Mar 30, 2012 6:47 AM, "Daniel Lee" <lee at isi-solutions.org> wrote:
>>>
>>> Hi there,
>>>
>>> I don't work too much with vectors, but my personal experience with them
>>> has been fairly slow, perhaps due to the topology. If you have access to the
>>> raw point cloud, you could try importing the ground and surface points as
>>> separate rasters using r.in.xyz and then use r.mapcalc to get the height by
>>> subtracting the ground from the surface raster. Or do you definitely need
>>> vector points as an output?
>>>
>>> Best,
>>> Daniel
>>>
>>> --
>>>
>>> B.Sc. Daniel Lee
>>> Geschäftsführung für Forschung und Entwicklung
>>> ISIS - International Solar Information Solutions GbR
>>> Vertreten durch: Daniel Lee, Nepomuk Reinhard und Nils Räder
>>>
>>> Deutschhausstr. 10
>>> 35037 Marburg
>>> Festnetz: +49 6421 379 6256
>>> Mobil: +49 176 6127 7269
>>> E-Mail: Lee at isi-solutions.org
>>> Web: http://www.isi-solutions.org
>>>
>>> ISIS wird gefördert durch die Bundesrepublik Deutschland,
>>> Zuwendungsgeber: Bundesministerium für Wirtschaft und Technologie aufgrund
>>> eines Beschlusses des Deutschen Bundestages, sowie durch die Europäische
>>> Union, Zuwendungsgeber: Europäischer Sozialfonds.
>>> Zusätzliche Unterstützung erhält ISIS von dem Entrepreneurship Cluster
>>> Mittelhessen, der Universität Marburg, dem Laboratory for Climatology and
>>> Remote Sensing und dem GIS-Lab Marburg.
>>>
>>>
>>>
>>>
>>> Am 29. März 2012 22:59 schrieb Daniel Victoria
>>> <daniel.victoria at gmail.com>:
>>>>
>>>> Hi all,
>>>>
>>>> I'm trying to calculate the height from the ground of several lidar
>>>> points (15million) in order to get the number of points that occur at
>>>> different height levels. I read some older posts about using r.in.xyz
>>>> (or r.in.lidar in grass 7) but I could not understand how to count the
>>>> number or points that have height from 0 to 5 m above the ground, for
>>>> instance. So, I'm trying to do the following.
>>>>
>>>> 1) import points using v.in.lidar (Grass 7 ubuntu linux)
>>>> 2) create a column in the database for the ground height and one for
>>>> elevation
>>>> 3) populate height column from ground raster (generate in another
>>>> process) using v.what.rast
>>>> 4) calculate elevation as zcoord - ground for each point (v.db.update)
>>>>
>>>> As you might imagine, this takes a long time. Just to import a 400Mb
>>>> lidar file takes around 50min.
>>>> Is there any easier way that I'm not envisioning?
>>>>
>>>> I'm running Grass 7 with liblas on a Ubuntu Virtual Machine and sqlite
>>>> backend.
>>>>
>>>> Thanks
>>>> Daniel
>>>> _______________________________________________
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>>>
>>>
>