[R-sig-Geo] Lidar data classification

[Georg Ruß]

On 17/03/11 11:38:19, Ervan Rutishauser wrote:
> Dear all,
>
> I would like to perform a classification of a large lidar data points
> acquired over a tropical forest plot network (500 km2).
> I computed the mean canopy(tree) height by 5m x 5m cell (pixel) and 3 others
> parameters (max height, height variation over 2 years, mean height in a 50m
> x 50 m neighborhood)
> I did most of this using the raster package.
> Now, I have a kind of multispectral image with 4 layers and I would like to
> perform a large-scale classification of the data based on these 4
> parameters. My aim is to find out "homogeneous" canopy regions, for
> instance: high canopy with low change over the 2 years, canopy gaps, areas
> of recruitment, etc.
>
> I tried to perfom a standard cluster analysis (hclust), but I could not
> compute the dissimilarity matrix (dist) on such a big data set (80'000 rows
> and 4 variables), even with a 64-bits PC.
> The k-means (kmeans{}) classification works, but return me strange results
> (4 main clusters north/south/east/west). I have seen that the biOps package
> allowed to do isodata classification. However isodata{} required an image
> and I don't know how to compute a 4-layer image (if possible).

Hi Ervan,

it seems you're up to doing some clustering on spatial data (which is
similar to classification here). In other words, you have a
spatialPointsDataFrame, and each of the points has four variables' values
attached (canopyheight, max height, ...).  The spatial data points are
uniformly (or on a grid) distributed in space, I guess.  

If the above is correct: I've developed something that can perform
exploratory clustering on this type of data sets. Nearly the same type of
data occur in precision agriculture and they want to find management zones
(management zone delineation): homogeneous areas inside a field. I'm
currently working on that task and it's part of my PhD thesis. If you
want, you can have a look at this publication of mine at last year's
precision agriculture conference:
http://fuzzy.cs.uni-magdeburg.de/aigaion/index.php/publications/show/772

I've written all of this in R and maybe we can have a look at the
clustering I've done. I think what you want is probably something that
gives you a first look at the data and helps you in delineating your
forest into zones, if that's what you want.

Regards,
Georg.
-- 
Research Assistant
Otto-von-Guericke-Universität Magdeburg
research at georgruss.de
http://research.georgruss.de