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rstringfilenamespaste

Extract date from LANDSAT8 image name (extention) in R

I would like to extract the date (YYDDD format) from LANDSAT8 folder names and use that in vegetation indexes calculated for multiple images (52).

Here is what I have so far:

setwd('E:/Landsat8')
folders <- list.dirs(full.names=FALSE, recursive = FALSE)

for(scene in folders){
  NIR <- raster(paste(scene,'/',scene,'_B5.TIF', sep=''))
  SWIR1 <- raster(paste(scene,'/',scene,'_B6.TIF', sep=''))
  LSWI <- overlay(x=NIR, y=SWIR1, fun=calcIndex)     #calculates LSWI 
  writeRaster(LSWI, filename=paste(scene,'/',scene,'_LSWI.TIF', sep=''), format='GTiff', datatype='FLT4S', overwrite=TRUE) 
  }

The format of the filenames from LANDSAT8 imagery looks like: LC81730382014069LGN00

I would like to safe the file as 2014_069_LSWI.TIF. At the moment it is saving it as LC81730382014069LGN00_LSWI.TIF I can't find the solution to only extract the date from the middle of the name string. Hopefully somebody has an idea!

Solution

  • If am not mistaken, year and day of year substrings in Landsat filenames are always at the same position. Therefore this should do it:

    #Sample image name
nm <- "LC81730382014069LGN00"

#Extract year
yr <- substr(nm, start=10, stop=13)

#Extract day of year
dy <- substr(nm, start=14, stop=16)

#Make name
nm2 <- paste(yr, dy, "LSWI.TIF", sep="_")

    You can then pass nm2 as the filename during writeRaster like as shown below. Note usage of paste0 ;-)

    writeRaster(LSWI, filename=paste0(scene,'/', nm2), format='GTiff', datatype='FLT4S', overwrite=T)