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Save kernel/filter matrix to use outside R

Source: R/filter_save.R
filter_save.Rd

This function saves a matrix with weights (filter or kernel matrix) in an external text file. It can save either the raw matrix or use the standards for running r.mfilter within GRASS GIS (with specific header and details).

Usage

filter_save(
  filt,
  radius,
  type,
  save_format = c("GRASS_rmfilter", "raw")[1],
  save_folder = NULL,
  save_file = NULL,
  divisor = 1,
  normalize = FALSE,
  parallel = TRUE,
  separator = " "
)

Arguments

filt

[matrix]
Filter or weight matrix, such as one created by filter_create() or terra::focalMat().

radius

[numeric(1)]
Radius of the Zone of Influence (ZoI) of the matrix, in meters.

type

[character(1)] Function for the kernel or filter matrix (see type parameter for filter_create()).

save_format

[character(1)="GRASS_rmfilter"]{"GRASS_rmfilter", "raw"}
Format in which the function should be saved. Currently, either of the two options:

  • GRASS GIS format for the module r.mfilter (save_format = "GRASS_rmfilter"), see details here);

  • raw matrix (save_format = "raw"), in which only the values of the matrix are printed.

save_folder

[character(1)=NULL]
Path to the folder where the matrix file should be written. If NULL, the current working directory is used.

save_file

[character(1)=NULL]
Name of the output file, generally a ".txt" file. If NULL, a standard filename is created, using the type and radius. E.g. "filter_bartlett2000.txt".

divisor

[numeric(1)=1]
By default, 1. This is the divisor of the neighborhood matrix when used within r.mfilter. According the the module documentation, "The filter process produces a new category value for each cell in the input raster map layer by multiplying the category values of the cells in the n x n neighborhood around the center cell by the corresponding matrix value and adding them together. If a divisor is specified, the sum is divided by this divisor."
If the divisor is zero, "then the divisor is computed for each cell as the sum of the MATRIX values where the corresponding input cell is non-null." In other words, the output map will be rescaled to the interval 0,1. If normalize = TRUE, the divisor is set to n*n.

normalize

[logical(1)=FALSE]
Whether the matrix should be normalized (sum of all cells is 1 if normalize = TRUE) or kept as it is (default, normalize = FALSE).

parallel

[logical(1)=TRUE]
Whether the computation should be paralelized or not (details in the documentation of the r.mfilter module).

separator

[character(1)=" "]
Separator between values of the matrix, within each line. Default is a space.

Value

None. The funcion only saves the input matrix as an external file.

Details

If used in the r.mfilter GRASS GIS module, "The filter process produces a new category value for each cell in the input raster map layer by multiplying the category values of the cells in the n x n neighborhood around the center cell by the corresponding matrix value and adding them together. If a divisor is specified, the sum is divided by this divisor." See details here.

See also

GRASS module r.mfilter

Examples

my_filter <- filter_create(r = 100, type = "bartlett", radius = 1000, round = 4)
filter_save(my_filter, radius = 1000, type = "bartlett", save_format = "GRASS_rmfilter")
filter_save(my_filter, radius = 1000, type = "bartlett", save_format = "raw")