Dear all,

I wonder if it is possible to compute a statistic (mean, max) of a
SpatialPointsDataFrame object using a SpatialGrid.
I tried it that way, but did not get what I wanted:

# 1. Create a grid bonding the region studied
Grid<-GridTopology(c(284600,580550),c(5,5),c(600,850))
Grid2<-SpatialGrid(Grid)

# 2. An example of my data
> head(temp)
         x                     y           z   R   G   B   I
1 284999.1 583538.0  9.76 11 10  8 65
2 284998.2 583537.1  6.40 10  4 11 69
3 284999.9 583536.1 28.70  8  8  4 75
4 284996.7 583535.9 12.55  4  3  0 63
5 284996.8 583533.8  7.64 16  6 10 75
6 284997.3 583532.5 26.46 11  9 10 74

coord<-coordinates(matrix(c(temp$x,temp$y),ncol=2))
Z<- data.frame(Z=temp$z,I=temp$I)
lidar<-SpatialPointsDataFrame(coord,Z)

test<-overlay(lidar, Para_gr) # I would like to compute the maximum of z in
each cell of the grid.

Thank you for any help.
All the best,
Ervan
______________________________________________________________________
Ervan Rutishauser
CIRAD - UMR AMAP 
PS1-Bd de la Lironde
34398 Montpellier cedex 5
phone: 04.67.61.58.00 



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