R: Read chunk data of a data cube from stdin or a file

read_chunk_as_array {gdalcubes} | R Documentation

## Read chunk data of a data cube from stdin or a file

### Description

This function can be used within function passed to `chunk_apply` in order to read a data cube chunk as a four-dimensional R array. It works only for R processes, which have been started from the gdalcubes C++ library. The resulting array has dimensions band, time, y, x (in this order).

### Usage

    read_chunk_as_array(with.dimnames = TRUE)

### Arguments

`with.dimnames` | if TRUE, the resulting array will contain dimnames with coordinates, datetime, and band names

### Value

four-dimensional array

### Note

Call this function ONLY from a function passed to `chunk_apply`.

This function only works in R sessions started from gdalcubes streaming.

### Examples

    # create image collection from example Landsat data only
    # if not already done in other examples
    if (!file.exists(file.path(tempdir(), "L8.db"))) {
      L8_files <- list.files(system.file("L8NY18", package = "gdalcubes"),
                             ".TIF", recursive = TRUE, full.names = TRUE)
      create_image_collection(L8_files, "L8_L1TP", file.path(tempdir(), "L8.db"))
    }

    L8.col = image_collection(file.path(tempdir(), "L8.db"))
    v = cube_view(extent=list(left=388941.2, right=766552.4,
                              bottom=4345299, top=4744931, t0="2018-01", t1="2018-12"),
                              srs="EPSG:32618", nx = 497, ny=526, dt="P1M")
    L8.cube = raster_cube(L8.col, v)
    L8.cube = select_bands(L8.cube, c("B04", "B05"))
    f <- function() {
      x <- read_chunk_as_array()
      out <- reduce_time(x, function(x) {
        cor(x[1,], x[2,], use="na.or.complete", method = "kendall")
      })
      write_chunk_from_array(out)
    }
    L8.cor = chunk_apply(L8.cube, f)
    plot(L8.cor, zlim=c(0,1), key.pos=1)

[Package gdalcubes version 0.3.1 Index]