[GRASS-user] Lidar points height from ground

[Daniel Victoria]

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
>
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>
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> 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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>
>
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