erodil_raster: Raster erosion and dilation

In kamapu/spatialist: Miscellaneous Spatial Functions

Raster erosion and dilation

Description

Mixing erosion and dilation processes to clean binary images, getting rid of isolated pixels and little holes.

For the single steps, see erode().

Usage

erodil_raster(raster, ...)

## S3 method for class 'SpatRaster'
erodil_raster(
  raster,
  width = c(3, 3),
  type = "diamond",
  erosion = TRUE,
  dilation = TRUE,
  erosion_first = TRUE,
  nt = 1,
  ...
)

Arguments

raster	An object of class SpatRaster containing 1 and 0 (or NAs) values.
...	Further arguments passed to shapeKernel().
width	An integer vector indicating the width and the heigth applied for the kernel. This is passed to shapeKernel().
type	A character value indicating the type of shape used for the kernel (see shapeKernel())
erosion	A logical value indicating whether the data will be eroded or not.
dilation	A logical value indicating whether the data will be dilated or not.
erosion_first	A logical value indicating whether erosion should be carried out before dilation or vice versa.
nt	Number of times to be processed.

Value

A SpatRaster object with value 1 for the processed features and 0 for the background. The output is already factorized and includes a color table for the two categories (white and black).

Author(s)

Jan Blöthe and Miguel Alvarez ([e-mail]).

Examples

## Load installed rasterLayer
require(terra)
require(ggplot2)
require(tidyterra)

# Import and prepare data
r <- rast(file.path(path.package("spatialist"), "binras.tif"))
r[is.na(r)] <- 0
r <- as.factor(r)
coltab(r) <- data.frame(value = c(0, 1), col = c("white", "black"))

## Make only erosion or only dilation
r2 <- rast(c(
    original = r,
    eroded = erodil_raster(r, dilation = FALSE),
    dilated = erodil_raster(r, erosion = FALSE)
))

ggplot() + geom_spatraster(data = r2) + facet_wrap(~lyr)

## Erode two times
r2 <- rast(c(
    original = r,
    dilated = erodil_raster(r, erosion = FALSE),
    dilated2 = erodil_raster(r, erosion = FALSE, nt = 2)
))

ggplot() + geom_spatraster(data = r2) + facet_wrap(~lyr)

## By default erosion will be done before dilation
r2 <- rast(c(
  original = r,
  eroded_first = erodil_raster(r),
  dilated_first = erodil_raster(r, erosion_first = FALSE),
  both = erodil_raster(erodil_raster(r, erosion_first = FALSE))
))

ggplot() + geom_spatraster(data = r2) + facet_wrap(~lyr)

kamapu/spatialist documentation built on Jan. 10, 2025, 6:59 p.m.