R: Filter data cube pixels by a user-defined predicate on band...

filter_pixel {gdalcubes} | R Documentation

## Filter data cube pixels by a user-defined predicate on band values

### Description

Create a proxy data cube, which evaluates a predicate over all pixels of a data cube. For all pixels that fulfill the predicate, the original band values are returned. Other pixels are simply filled with NANs. The predicate may access band values by name.

### Usage

    filter_pixel(cube, pred)

### Arguments

`cube` | source data cube
`pred` | predicate to be evaluated over all pixels

### Details

gdalcubes uses and extends the tinyexpr library to evaluate expressions in C / C++, you can look at the library documentation to see what kind of expressions you can execute. Pixel band values can be accessed by name.

### Value

a proxy data cube object

### Note

This function returns a proxy object, i.e., it will not start any computations besides deriving the shape of the result.

### 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="2018-06"),
                  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"))
    L8.ndvi = apply_pixel(L8.cube, "(B05-B04)/(B05+B04)", "NDVI")
    L8.ndvi.filtered = filter_pixel(L8.ndvi, "NDVI > 0.5")
    L8.ndvi.filtered

    plot(L8.ndvi.filtered)

[Package gdalcubes version 0.6.0 Index]