Alexandre, boa tarde!

Fiz algumas alterações em cima do seu CMR. Veja se há algo que possa lhe servir.

#<code r>
setwd('C:/LAB/RBASICS/tmp'); getwd()
require(raster); require(rgdal)

### Download a partir de uma lista de links
##############################################################################
### A opção "get link" gera algo como "https://www.dropbox.com/s/XXXXXX/file.png"
### para download.file() Use "XXXXXX/file.png" após "http://dl.dropbox.com/s/"
### XXXXXX = token

### links obtidos no seu script
links <- c(
"https://www.dropbox.com/s/8b99gn9ve1yo7is/Fig1-0_00_00.png", 
"https://www.dropbox.com/s/8b99gn9ve1yo7is/Fig2-0_20_00.png", ### erro! mesmo token do anterior!
"https://www.dropbox.com/s/bo6gbt3ca6xwxm0/Fig3-0_40_00.png")

tokens    <- gsub("^.*/s/","",dirname(links))
fileNames <- basename(links)
newLinks  <- file.path("http://dl.dropbox.com/s", tokens, fileNames); newLinks

for (a in newLinks) {
          tryCatch(download.file(a, dest=basename(a), mode='wb'),
                              error=function(...) print("Falha no download!"))} 

### Verificando arquivos baixados corretamente
##############################################################################
fileInfo  <- file.info(fileNames); fileInfo ### observe o segundo arquivo
files.OK  <- fileNames[fileInfo$size>0 & !is.na(fileInfo$size)]; files.OK

### Operando arquivos baixados corretamente
##############################################################################
for (b in files.OK) {
          t       <- strsplit(b,"-|\\.")[[1]][2]
          tempo   <- gsub("_", ":", t)
          r       <- raster(b); #image(r) ### comentado para otimizar
          XYZ     <- data.frame(coordinates(r), values(r), rep(tempo))
          XYZ.0   <- XYZ[XYZ[,3]==0,]
          outName <- paste0('XYZ.0-', t, '.txt')
          write.table(XYZ, outName, row.names=F)
          message(noquote(paste(outName, "salvo em", getwd()))) 
}
#</code>



Éder Comunello <comunello.eder@gmail.com>
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