ループ機能を使用して複数のラスターファイルを再投影する方法

Question

Rで複数の.tifファイルを処理しようとしましたが、.tifファイルを再作成したいと思っていました。私はそれに取り組んでいる間、私は次のコードを実行しました。私は次のようなエラーに

Error in .rasterObjectFromFile(x, band = band, objecttype = "RasterLayer", : 
    Cannot create a RasterLayer object from this file. 
In addition: There were 20 warnings (use warnings() to see them) 
Warning messages: 
1: In if (filename == "") { ... : 
    the condition has length > 1 and only the first element will be used 
2: In if (!file.exists(dirname(filename))) { ... : 
    the condition has length > 1 and only the first element will be used 
3: In if (toupper(x@file@name) == toupper(filename)) { ... : 
    the condition has length > 1 and only the first element will be used 
4: In if (trim(filename) == "") { ... : 
    the condition has length > 1 and only the first element will be used 
5: In if (!file.exists(dirname(filename))) { ... : 
    the condition has length > 1 and only the first element will be used 
6: In if (filename == "") { ... : 
    the condition has length > 1 and only the first element will be used 
7: In if (file.exists(filename)) { ... : 
    the condition has length > 1 and only the first element will be used 
8: In if (nchar(filename) == 0) stop("empty file name") : 
    the condition has length > 1 and only the first element will be used 
9: In if (x == "" | x == ".") { ... : 
    the condition has length > 1 and only the first element will be used 
10: In if (!start %in% c("http", "ftp")) { ... : 
    the condition has length > 1 and only the first element will be used 
11: In if (fileext %in% c(".GRD", ".GRI")) { ... : 
    the condition has length > 1 and only the first element will be used 
12: In if (!file.exists(x)) { ... : 
    the condition has length > 1 and only the first element will be used 
13: In if ((fileext %in% c(".HE5", ".NC", ".NCF", ".NC4", ... : 
    the condition has length > 1 and only the first element will be used 
14: In if (fileext == ".GRD") { ... : 
    the condition has length > 1 and only the first element will be used 
15: In if (fileext == ".BIG" | fileext == ".BRD") { ... : 
    the condition has length > 1 and only the first element will be used 
16: In if (fileext %in% c(".BIN")) { ... : 
    the condition has length > 1 and only the first element will be used 
17: In if (fileext == ".DOC") { ... : 
    the condition has length > 1 and only the first element will be used 
18: In if (fileext %in% c(".SGRD", ".SDAT")) { ... : 
    the condition has length > 1 and only the first element will be used 
19: In if (nchar(filename) == 0) stop("empty file name") : 
    the condition has length > 1 and only the first element will be used 
20: In if (!file.exists(x)) { ... : 
    the condition has length > 1 and only the first element will be used 

誰もがこの点で私を助けることができるのだコードを実行した後

#convert into raster and reproject 
mylist <- list.files(path='mydir', pattern = "*.tif$") 
fname <- substr(mylist, 1,20) 
fn <- paste0('prj',fname, '.tif') 
newproj <- "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0" 
for (i in 1:4){ 
    temprast <- raster(mylist[i]) 
    prj<-projectRaster(temprast, crs=newproj, method = 'bilinear') 
    writeRaster(prj, filename = fn, format='GTiff', overwrite=T) 
} 

？ ありがとう

Answer 1

fnにファイル名のベクトルfn[i]の代わりに1つのファイル名を書き込もうとすると、警告が表示されます。つまり、最初の要素fn[1]に4回書き込みます。私には、エラーメッセージがどこから来たのかは不明ですが、それも消えてしまうことが予想されます。

以下はクリーンアップ版です。私はmylistをffに変更しました。mylistは、Rの意味で "リスト"ではないため、悪い名前です（list.filesは文字ベクトルを返します）。また、*は無意味でした。そして私はsubstr(, 1,20)より一般的なアプローチを使用しています。さらに、writeRasterと別の手順で行うのではなく、projectRasterというファイルに書き込むほうが効率的です。ラスタが同程度と解像度を持っている場合は

ff <- list.files(path='mydir', pattern = "\\.tif$") 
fn <- gsub("\\.tif$", "_prj.tif", ff) 
newproj <- "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0" 

for (i in 1:4){ 
    r <- raster(ff[i]) 
    prj <- projectRaster(r, crs=newproj, method = 'bilinear', filename = fn[i], overwrite=TRUE) 
} 

は、あなたも行うことができます。

ff <- list.files(path='mydir', pattern = "\\.tif$") 
s <- stack(ff) 
newproj <- "+proj=longlat +datum=WGS84" 
prj <- projectRaster(s, crs=newproj, method ='bilinear', filename='prj.tif')