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
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
>
>
>
>
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