[Liblas-devel] Ground Modeling with RAW LiDAR and libLAS

[Stuart Edwards]

I don't find it to be particularly slow .... I guess it depends on how much processing you have to do.  My uses are fairly limited so it's not a problem.

Not quite on topic, but close, and something I'm trying to figure out -- the LibLAS decoded file can provide all of the point data - not just x,y,z.  This includes identification of 1st and 2nd arrivals which helps a lot in discerning vegetal cover from the ground surface.  

However, if you are going to filter on arrival time to get a ground surface data set you have to eliminate the 1st arrivals - but only if there's a second. If a second is absent (no vegetation at that location) then the 1st becomes the 'last' too.  This makes interpretation more complicated and not just a matter of separating the 1s and 2s.  I ended up writing a short script in octave to split the data into two pools - first arrivals and true last arrivals using the simple notion that a 1 is only a first if it is followed by a 2.  If not, it's a last. 

 Has anyone else wrestled with this?

Stu


On Mar 4, 2011, at 9:29 AM, francesco wrote:

> I use GRASS quite a lot, but always thought that it would be slow on vector points. I know Brovelli and her team developed some modules, I'll check on that. Good idea to use LibLAS as "driver" to turn LAS to xyz.
> Francesco
> 
> Il 04/03/2011 15:05, Stuart Edwards ha scritto:
>> 
>> GRASS GIS (open source) has several modules for processing raw LiDAR data and the ability to script your own classification routines.  LibLAS does a nice job of preprocessing (decoding) the LAS files so they can be input to GRASS as x,y,z or general ASCII format .......see:
>> 
>>  http://grass.osgeo.org/wiki/LIDAR#Micro-tutorial
>> Stu
>> 
>> 
>> On Mar 4, 2011, at 1:31 AM, francesco wrote:
>> 
>>> Hello List, 
>>> I just registered, hello to everyone. 
>>> Regarding Aaron's question, I am playing around with LibLAS to develop a ground classification procedure. It uses Axellson's progressive triangulation of local minimum points - but I am also looking at other solutions. Does anyone have other interesting approaches in mind?
>>> Cheers,
>>> Francesco
>>> -- 
>>> **************************************************
>>> Francesco Pirotti
>>> Dep. TESAF 
>>> CIRGEO – Interdepartmental Research Center on Cartography Photogrammetry 
>>> Remote Sensing and G.I.S. 
>>> University of Padova 
>>> Web: http://www.cirgeo.unipd.it/cirgeo/francescopirotti.htm
>>> Email: francesco.pirotti at unipd.it
>>> Phone: +39 049 827 2710 
>>> Phone: +39 349 55 39 261
>>> **************************************************
>>> 
>>> 
>>> Il 04/03/2011 00:49, Aaron Reyna ha scritto:
>>>> 
>>>> Ah yes,
>>>> 
>>>> I'll try the MCC-LiDAR. Great, thanks for the suggestion!
>>>> 
>>>> Aaron 
>>>> 
>>>> On Thu, Mar 3, 2011 at 3:09 PM, Peter Tittmann <pwtittmann at ucdavis.edu> wrote:
>>>> I've used MCC-Lidar http://sourceforge.net/apps/trac/mcclidar/ a little with marginal results. Not a great answer but something. TeraScan http://www.terrasolid.fi/en/products/terrascan is the elephant in that room.
>>>> 
>>>> Peter
>>>> 
>>>> 
>>>> On 03/03/2011 02:43 PM, Aaron Reyna wrote:
>>>>> This may be too broad of a question, but has anyone seen or heard of a way to do efficient ground modeling with libLAS? That is, take raw LiDAR files (all default points) and model out the ground class? I do have raw LiDAR files if                               it helps.
>>>>> 
>>>>> Just throwing it out there.
>>>>> 
>>>>> Best,
>>>>> 
>>>>> Aaron 
>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> Liblas-devel mailing list
>>>>> Liblas-devel at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/liblas-devel
>>>> 
>>>> -- 
>>>> Peter Tittmann
>>>> Geography Graduate Group
>>>> UC Davis
>>>> c. 707 849 4135
>>>> 
>>>> 
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>>> 
>>> 
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>> 
> 
> 
> -- 
> **************************************************
> Francesco Pirotti 
> Dep. TESAF 
> CIRGEO – Interdepartmental Research Center on Cartography Photogrammetry 
> Remote Sensing and G.I.S. 
> University of Padova 
> Web: http://www.cirgeo.unipd.it/cirgeo/francescopirotti.htm 
> Email: francesco.pirotti at unipd.it 
> Phone: +39 049 827 2710 
> Phone: +39 349 55 39 261
> **************************************************
> _______________________________________________
> Liblas-devel mailing list
> Liblas-devel at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/liblas-devel

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