Re: [LAStools] math behind lasground

[Markus Gerke]

Hi!
As far as I know it is based on the mesh simplification approach by
Axelsson:

Axelsson, P., 1999. Processing of laser scanner data - algorithms
and applications. ISPRS Journal of Photogrammetry and Re-
mote Sensing 54(2-3), pp. 138�147.

Markus

On 09/19/2013 04:57 AM, svfilhol wrote:
> hi,
>
> Could you provide some more information about the algorithm running
> from lasground? I am using lastool for research, and I need to know
> what process lasground is using to classify the points.
> thx
> Simon
>
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[Ruben Valbuena]

Well, if it is true that Axelsson's mesh simplification is implemented, then the publication you are looking for is not that one, but a subsequent one (Axelsson, 2000-the adaptive TIN model).

But, is it?
Is this information true?
Martin, may you please corroborate of deny this point?

-----Original Message-----
From: last...@googlegroups.com [mailto:last...@googlegroups.com] On Behalf Of Markus Gerke
Sent: 19 September 2013 10:20
To: last...@googlegroups.com
Subject: Re: [LAStools] math behind lasground

Hi!
As far as I know it is based on the mesh simplification approach by
Axelsson:

Axelsson, P., 1999. Processing of laser scanner data - algorithms and applications. ISPRS Journal of Photogrammetry and Re- mote Sensing 54(2-3), pp. 138-147.

[svfilhol]

Thanks Markus and Ruben for these two references.
After reading them, I still struggle on how this algorithm decides wether or not a point is "ground". And knowing that the point density of ground based LiDAR data is varying widely in space, how applicable is this method for classifying ground for non airborne data?
Thanks
Simon

PS: my apologize for posting twice the same question in the google group, this was my first time using google group ever.

[Ruben Valbuena]

The algorithm explained there depends on two parameters: (1) a search window and (2) a maximum angle criteria. Low points are decided as ground and a TIN is interpolated among them. The TIN is simplified by the criteria at each iteration. The parameters are to be decided manually, so in principle it could be used for any type of scan, just lowering the parameters at finer scales.

 

But I keep doubting that this is the algorithm used in lasground. Wait for Martin’s answer.

 

Note that the tool contains a switch for '-not_airborne', so the answer is yes. If density varies, I would set parameters for the less dense parts.

 

 

From: last...@googlegroups.com [mailto:last...@googlegroups.com] On Behalf Of svfilhol
Sent: 19 September 2013 21:18
To: last...@googlegroups.com
Subject: Re: [LAStools] math behind lasground

 

Thanks Markus and Ruben for these two references.

[henry]

I am using lastool for research, and I also need to know what process lasground is using to classify the points. Could you provide some more information about the algorithm running from lasground? Or can you introduce some papers?
Thank you very much! I'm looking forward to your early reply.
在 2013年9月20日星期五UTC+8上午5时18分52秒，Ruben Valbuena写道：

[João Paulo Pereira]

Hello, did anyone find the answer for this question? Is really an adaptive TIN filter used in lasground?

Thanks

[Sarah Kandrot]

I want to know the answer too!  I want to include a discussion on feature extraction tools in a section of my literature review, and this technique is an enigma to me...

Thanks!

-Sarah

[Adam Erickson]

Add me to the group of those who are curious of the algorithm source for lasground :)

Cheers,

Adam

[Martin Isenburg]

Hello,

lasground uses a variation of the Axellson 2000 TIN refinement algorithm that avoids some of the trigonometry overhead. In fact rapidlasso just spent to weeks at their "secret beach laboratories" [1] to rework lasground completely for more robustness in complex and steep terrains mixed with urban housing areas (no chopping off mountain tops while also removing houses while retaining river banks and other terrain subtelties) by operating at multiple scales. This lasground_new will be available for use alongside the original lasground in the next release. Very curious peeps can ask for a pre-release version via a request to lasg...@rapidlasso.com ...

[1] http://www.facebook.com/LAStools/photos/835965953132517

Martin @rapidlasso

--

http://rapidlasso.com - fast tools to ground your LiDARs

[Alessandro Montaghi]

H

​​

i

​ All​

,

I am pretty sure that also Terrascan classification algorithom use a the Axellson 2000 TIN refinement algorithm because a postodoc of the Danish team of scalgo company (https://scalgo.com/) rewrote with a Reverse engineering approach the Axellson's algorithm to understand how Terrascan works. For my point of view all classification algorithms are heuristic techniques in order to speed the classification of milions of points

​.​

 

​PS: nobody (especially companies) share the algorthims 100%!

Alessandro ​