R: Filter data cube pixels by a polygon

filter_geom {gdalcubes} | R Documentation

## Filter data cube pixels by a polygon

### Description

Create a proxy data cube, which filters pixels by a spatial (multi)polygon For all pixels whose center is within the polygon, the original

### Usage

    filter_geom(cube, geom, srs = NULL)

### Arguments

`cube` | source data cube
`geom` | either a WKT string, or an sfc or sfg object (sf package)
`srs` | string identifier of the polygon's coordinate reference system understandable for GDAL

### Details

The resulting data cube will not be cropped but pixels outside of the polygon will be set to NAN.

If `geom` is provided as an sfc object with length > 1, geometries will be combined with `sf::st_combine()` before.

The geometry is automatically transformed to the data cube's spatial reference system if needed.

### 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")
    WKT = gsub(pattern='\\n',replacement="",x =
      "Polygon ((-74.3541 40.9254,
                 -73.9813 41.2467,
                 -73.9997 41.4400,
                 -74.5362 41.1795,
                 -74.6286 40.9137,
                 -74.3541 40.9254))")
    L8.ndvi.filtered = filter_geom(L8.ndvi, WKT, "EPSG:4326")
    L8.ndvi.filtered

    plot(L8.ndvi.filtered)

[Package gdalcubes version 0.6.0 Index]