Extracting Temperature by exactextractr

Enviado: segunda-feira, 24 de outubro de 2022 10:52
Para: r-sig-geo at r-project.org <r-sig-geo at r-project.org>
Assunto: [R-sig-Geo] Extracting Temperature by exactextractr

Hello everyone, I am getting the year 2016 monthly average temperature for my shapefile polygons.

My data is cru_ts4.05.2011.2020.tmp.dat.nc

Follow my code. And at the end of the code my questions, if you can help.

Rasterdata <- cruts2raster("cru_ts4.05.2011.2020.tmp.dat.nc",
                      timeRange=c("2016-01-01","2017-01-01"))

rasterdata

# # checking raster crs
cat(wkt(crs(rasterdata)), "\n")

# getting shapefile

datasets <- list_geobr()

print(datasets)

micro <- read_micro_region(year=2013)

options(max.print = 9999)

print(micro[3:4],n=558)

sf::sf_use_s2(TRUE)
sf::st_is_longlat(micro)

#  checking CRS Shapefile.

st_crs(micro)

#switching to the same CRS as the raster to do extraction.

shape<-st_transform(micro, crs(rasterdata))

st_crs(shape)
#same.

#doing extraction through exact_extract.

weath_dt = as.data.frame(matrix(NA,nrow(micro),14))
weath_dt[,1] = shape$code_micro
weath_dt[,2] = shape$name_micro

for (i in 1:length(rasterdata at layers)) {
  weath_dt[,2+i] = exactextractr::exact_extract(rasterdata[[i]], shape, 'mean')
}

#generating average

#checking for Na

apply(weath_dt, 2, function(x) {sum(is.na(x))})

#all very well.

library(dplyr)

weath_dt[,15] <- rowMeans(weath_dt[,3:14])

shape$avetemp <- weath_dt[,15]

print(shape[6:7],n=558)

st_write(shape, dsn = ".", layer = "SHAPE.shp", driver = "ESRI Shapefile")

My questions:

#Code is OK?
#Any problem with the resolution or size of the polygons to the result of the extraction?
# From what I've seen the algorithm already considers the weighted average by the fraction of the cell that covers the polygon. I think it would be better than the simple average, right?
#result generated are in shapefile ID order?
#how to put raster CRS in 4326 before extraction? So, the shapefile's CRS would also end up in 4326. I believe they are in WGS 84 would this generate the same result for my extractions if they were in EPSG 4326?

Thanks.

Pietro Andre Telatin Paschoalino
Doutor em Ci?ncias Econ?micas pela Universidade Estadual de Maring? - PCE.
Professor tempor?rio do departamento de Economia da UEM.

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