更改大型栅格中的单个像元值

Question

我有一个栅格砖，上面有岛屿的气候数据层，周围环绕着 NA 海洋细胞。我想将一些海洋单元格设置为附近海岸的值。这样做有很多麻烦。在我看来，代码应该如下所示，但我的内存不足。栅格大小约为 2500x2500。

# dummy stack with three layers
slogo <- stack(system.file("external/rlogo.grd", package="raster")) 
# let's say cell 5 is the one I want to change
newvals <- 1000*(1:3)
for(i in 1:nlayers(slogo)) slogo[[i]][5] <- newvals[i]

随后的步骤是将栅格写入单独的 ascii 文件；因此，另一种 hacky 解决方案可能是剪切到文本文件中并替换单个值...

编辑： 也许有人可以通过重置内存分配限制来推荐解决方案？这是我在大型栅格上运行后显示的错误消息。 Error: cannot allocate vector of size 504.1 Mb In addition: Warning messages: 1: In readBin(raster@file@con, what = dtype, n = nc, dsize, dsign, : Reached total allocation of 3979Mb: see help(memory.size) 2: In readBin(raster@file@con, what = dtype, n = nc, dsize, dsign, : Reached total allocation of 3979Mb: see help(memory.size) 3: closing unused connection 4 (C:\Users\jcw\AppData\Local\Temp\R_raster_jcw\r_tmp_2015-08-16_130255_2000_11926.gri) 4: In getBilData(object, r = startrow, nrows = nrows, c = startcol, : Reached total allocation of 3979Mb: see help(memory.size) 5: In getBilData(object, r = startrow, nrows = nrows, c = startcol, : Reached total allocation of 3979Mb: see help(memory.size) 6: In getBilData(object, r = startrow, nrows = nrows, c = startcol, : Reached total allocation of 3979Mb: see help(memory.size) 7: In getBilData(object, r = startrow, nrows = nrows, c = startcol, : Reached total allocation of 3979Mb: see help(memory.size)

Answer 1

你已经很接近了，这只是一个索引问题：

library(raster)

# dummy stack with three layers
slogo <- brick(system.file("external/rlogo.grd", package="raster")) 

##  Check values of all three bands at cell 5:
slogo[5]

产量：

     red green blue
[1,] 255   255  255

##  Set values of all three bands to zero:
slogo[5][1:3] <- 0

slogo[5]

产量：

     red green blue
[1,]   0     0    0

一种可能使 OP 克服一次处理所有波段的内存问题的替代方法：

##  Alternatively, load each band into memory separately, do the
##    replacement and write each band back to disk as a separate GeoTiff:
for (i in 1:nbands(slogo)) {
    r <- raster(slogo, layer=i)
    r[5] <- 0
    writeRaster(r, file=paste0("band_", i, ".tif"), format="GTiff")
}

Answer 2

您可以使用raster::update 函数来更改磁盘上光栅文件中的值（请务必进行备份！）