Set mask band of a VRT collection

Masking functions VRT pixel functions.

Usage

vrt_set_maskfun(
  x,
  mask_band,
  mask_values,
  build_mask_pixfun,
  set_mask_pixfun,
  drop_mask_band,
  cache_dir
)

# S3 method for class 'vrt_block'
vrt_set_maskfun(
  x,
  mask_band,
  mask_values,
  build_mask_pixfun = vrtility::build_intmask(),
  set_mask_pixfun = vrtility::set_mask_numpy(),
  drop_mask_band = TRUE,
  cache_dir = getOption("vrt.cache")
)

# S3 method for class 'vrt_collection'
vrt_set_maskfun(
  x,
  mask_band,
  mask_values,
  build_mask_pixfun = vrtility::build_intmask(),
  set_mask_pixfun = vrtility::set_mask_numpy(),
  drop_mask_band = TRUE,
  cache_dir = getOption("vrt.cache")
)

set_mask_numpy()

build_intmask()

build_bitmask()

Arguments

x: A VRT collection
mask_band: The name of the mask band
mask_values: A numeric vector of integer or bit values to be masked.
build_mask_pixfun: A character string of the Python code to build the mask. Provided functions include build_intmask() and build_bitmask(). See details.
set_mask_pixfun: A character string of the Python code to set the mask. Provided functions include set_mask_numpy(). See details.
drop_mask_band: Logical. If TRUE, the mask band will be removed from the VRT block.
cache_dir: A character string of the directory to use for temporary files. In general this should be left alone. main purpose is to manage cache location when running asyncronously with mirai.

Value

A VRT block with the mask band set.

A VRT collection with the mask band set.

Details

The build_mask_pixfun function is used to build the mask band. Where the mask band is a true bitmask and bit-wise operations are required, the build_bitmask() function should be used. For integer-based masking, where the mask band is provided as a single band with integer values, the build_intmask() function should be used.

The set_mask_pixfun function is used to apply the mask to the other bands. In general set_mask_numpy() should be used, although a custom function can be provided.

set_mask_numpy simply applies a given mask where values of 0 are assumed to have nodata and values > 0 (typically 255) contain valid data. It is the only provided function for the set_mask_pixfun argument in vrt_set_maskfun(). Alternatively a custom function could be provided if, for example a user wishes to buffer the mask.

build_intmask provides an integer mask function that can be used to mask out pixels based on a band containing true integer/numeric values. This would be appropriate for the Sentinel 2A SCL band, for example.

build_bitmask provides is a simple bit-wise mask function that can be used to mask out pixels based on a true bit mask. This function should be used where bitwise operations are required. e.g. for HLS data, the "Fmask" band requires bitwise operations to extract the mask values.

Examples

s2files <- fs::dir_ls(system.file("s2-data", package = "vrtility"))

ex_collect <- vrt_collect(s2files)
ex_collect |>
  vrt_set_maskfun(
    mask_band = "SCL",
    mask_values = c(0, 1, 2, 3, 8, 9, 10, 11),
    drop_mask_band = FALSE)
#> → <VRT Collection>
#> Mask Function: [hidden]
#>   run print(x, maskfun = TRUE) to view
#> 
#>  VRT SRS: 
#> PROJCS["unknown",GEOGCS["unknown",DATUM["Unknown based on WGS 84 ellipsoid",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_center",50.72],PARAMETER["longitude_of_center",-3.51],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1],AXIS["Easting",EAST],AXIS["Northing",NORTH]]
#> 
#>  PROJCS["WGS 84 / UTM zone 30N",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-3],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","32630"]]
#> 
#>  PROJCS["OSGB36 / British National Grid",GEOGCS["OSGB36",DATUM["Ordnance_Survey_of_Great_Britain_1936",SPHEROID["Airy 1830",6377563.396,299.3249646,AUTHORITY["EPSG","7001"]],AUTHORITY["EPSG","6277"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4277"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",49],PARAMETER["central_meridian",-2],PARAMETER["scale_factor",0.9996012717],PARAMETER["false_easting",400000],PARAMETER["false_northing",-100000],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","27700"]]
#> 
#> 
#> Bounding Box: NA
#> Pixel res: 19.9923198093722, 19.9923198093722
#> Start Date: NA
#> End Date: NA
#> Number of Items: 5
#> Assets: B02, B03, B04, SCL