[R-sig-Geo] Advice on clustering LiDAR point clouds

[Dylan Beaudette]

On Tuesday 18 August 2009, Etienne Bellemare Racine wrote:
> Hi Wesley,
>
> It is unclear to me if you want to aggregate points to distinguish
> individual tree, or if you want to locate the treetops ?
>
> Anyway, I suggest you first use your grid to locate treetops (using
> maximum value as you said), then clustering using the treetops. Is your
> plantation dense ? because if the crowns are touching each other, I
> think it will be pretty hard to cluster them using only points. If you
> have treetops, you can aggregate points around individuals treetops.
>
> To get maximum values, maybe sp::overlay can get you started, but I
> think it is more to get grid value to point than reverse. I do it in
> ArcGIS, but I would be happy to have a solution in R if you find one.
>
> Etienne

Also see r.in.xyz within GRASS GIS.

Dylan

>
> Wesley Roberts a écrit :
> > Dear R-sig-Geo,
> >
> > I am currently looking at clustering a LiDAR point cloud (trees in a
> > plantation forest) using R and have some questions that I hope some of
> > you may be able to answer.
> >
> > My method is a two stage approach, firstly I selected potential tree
> > locations by overlaying a static grid on the point data and selecting the
> > maximum value within each grid. These locations were stored as potential
> > tree locations and have been used as sample data in a spatial clustering
> > approach (I would have liked to use a moving filter but could not find a
> > local maximum approach implemented in R). These points and the original
> > data are now being clustered using the clus algorithm in the spatclus
> > package.
> >
> > My query regards the use of an algorithm developed for disease mapping
> > (Kuldorff's circular zone in 2D) with Lidar data. The density of the
> > lidar points is around 5 per square meter and I am concerned that the
> > algorithm will not be able to identify clusters based on height. I am yet
> > to inspect the results as the clus algorithm is still running so I cant
> > comment on that right now, but I was wondering if anyone on the list had
> > any suggestions wrt the clustering and or segmentation of lidar point
> > clouds using R. I am unwilling to use interpolation as I want to avoid
> > the lengthy process of selecting the correct interpolation procedure and
> > or model and would like to stick with the point cloud.
> >
> > Any advice on this matter would be greatly appreciated.
> > Many thanks and kind regards,
> >
> > Wesley
> >
> >
> > Wesley Roberts MSc.
> > Researcher: Earth Observation
> > Natural Resources & the Environment (NRE)
> > CSIR
> > Tel: +27 (0)21 888-2490
> > Fax: +27 (0)21 888-2693
> > "To know the road ahead, ask those coming back."
> > - Chinese proverb
>
> 	[[alternative HTML version deleted]]



-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341