Sunday, 6 August 2017

r - Extracting values from raster according to Lat and long of values?


having 12 files with 12 hdrs for one year: these files are raster (projected WGS84,lat long):


          samples = 1440

lines = 720
bands = 1
header offset = 0
file type = ENVI Standard
data type = 4
interleave = bsq
byte order = 0
map info = { Geographic Lat/Lon, 1, 1, -180, 90, 0.25, 0.25,WGS-84}
coordinate system string = GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",
SPHEROID["WGS_1984",6378137,298.257223563]]

,PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]
}

These lines will open the files as a list:


      a<-list.files("D:\\ECV\\2010", "*.envi", full.names = TRUE)
for(i in 1:length(a)){
d <- raster(a[i]}

I would like to extract the values correspond to 44.8386° N, 0.5783° W from all files as txt file



Answer




Curlew's answer can be improved upon like this (do not use a loop, and use a RasterStack)


library(raster)
files <- list.files("D:\\ECV\\2010", "*.envi", full.names = TRUE)
s <- stack(files)
point <- cbind(44.8386, 0.5783)
result <- extract(s, point)

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