Saturday 28 July 2018

How to get feature values from multiple polygons of shapefile while using extract function on raster


I have a shapefile which contains arround 800 circular polygons with diameter of 60 meters each. Raster is 20 meter resolution so I would have multiple cell values extracted for each polygon. I am using an extract function on multiple raster layers in a for loop, and am putting the results in the dataframe. I know i can get the cellnumbers within the extract function, but I would also like to obtain the feature values (in my case a column in attribute table containing specific polygon code) directly from the shapefile for each pixel value extracted. Thus I would have in one row a pixel cell number, its extracted value and the polygon code.


my code:



dirs=list.dirs(full.names=TRUE)
dirs=dirs[grepl("R20",dirs)]
dirs=as.list(dirs)

DataToWrite=list()
sumirana=data.frame()
for (j in 1:length(dirs)) {
setwd(paste("E:/",as.character(dirs[j]),sep="/"))
files=list.files(full.names=FALSE,pattern="*20m*.tif$")
for (i in 1:length(files)) {

curRaster=raster(paste(getwd(),files[i],sep="/"))
rasterOut=(na.omit(extract(curRaster,azo_plohe, cellnumbers=TRUE,
weights=TRUE, df=TRUE)))
if((length(rasterOut) > 1)) {

DataToWrite=c(DataToWrite,rasterOut[3])

} else {

lista=list(rep("x",15))

tablica_folder=as.data.frame(t(unlist(lista)))
colnames(tablica_folder)=c(1:15)
}
}
if((length(rasterOut) > 1)) {
mylist=as.data.frame(DataToWrite)
naziv_fajla=as.vector(rep((substr((names(DataToWrite)
[1]),50,55)),nrow(mylist)))
tablica_folder=as.data.frame(c(rasterOut[2],naziv_fajla[1],
rasterOut[4],mylist),col.names=c(1:15))

sumirana=rbind(sumirana,tablica_folder)
DataToWrite=list()

} else {
sumirana=rbind(sumirana,tablica_folder)
}
}


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