Package 'simsam'

Blend rasters based on a provided formula

Description

Blend rasters based on a provided formula

Usage

blend_rasters(x, formula, ...)

Arguments

x	A SpatRaster object with one or more layers
formula	A formula specifying how to combine the rasters
...	Additional SpatRaster objects to blend

Value

A SpatRaster object with the combined layers

Examples

rast_grid = terra::rast(ncols = 300, nrows = 100,
  xmin = 0, xmax = 300, ymin = 0, ymax = 100)

sf1 = sim_covariates(
  rast_grid,
  n = 4,
  method = simulate_gaussian(range = 25)
)

g1 = blend_rasters(sf1, ~ cov1 + cov4)
g2 = blend_rasters(g1, ~ outcome^2 + (cov2 + 2), sf1)

terra::plot(g1)
terra::plot(g2)

---

Generate spatial proxies

Description

The make_proxy() function generates spatial proxies for a given raster object. It generates spatial proxies such as:

• coordinates

• Euclidean Distance Fields (EDF)

• Oblique Geographic Coordinates (OGC)

Usage

make_proxy(rast_grid, method = proxy_coordinates())

add_proxy(rast_grid, method = proxy_coordinates())

Arguments

rast_grid	A SpatRaster
method	A proxy method created by ⁠proxy_*()⁠ functions

Value

A SpatRaster object

SpatRaster

References

Behrens, T., Schmidt, K., Viscarra Rossel, R. A., Gries, P., Scholten, T., & MacMillan, R. A. (2018). Spatial modelling with Euclidean distance fields and machine learning. European journal of soil science, 69(5), 757-770.

Møller, A. B., Beucher, A. M., Pouladi, N., & Greve, M. H. (2020). Oblique geographic coordinates as covariates for digital soil mapping. Soil, 6(2), 269-289.

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

proxy_coords = make_proxy(rast_grid, proxy_coordinates())
proxy_edf = make_proxy(rast_grid, proxy_edf())
proxy_ogc = make_proxy(rast_grid, proxy_ogc(n = 5))

terra::plot(proxy_coords)
terra::plot(proxy_edf)
terra::plot(proxy_ogc)

---

Coordinate proxy factory

Description

Returns a function that generates coordinate layers (X, Y) for a raster.

Usage

proxy_coordinates()

Value

A function that accepts rast_grid and returns a SpatRaster

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

make_proxy(rast_grid, proxy_coordinates())

---

Euclidean Distance Field proxy factory

Description

Returns a function that generates Euclidean Distance Fields from specified locations (default: four corners and center of the raster extent).

Usage

proxy_edf(coords = NULL)

Arguments

coords

Optional coordinates. Can be a matrix, data frame, sf, or SpatVector with x and y columns. If NULL, uses default locations: four corners and center of the raster extent.

Value

A function that accepts rast_grid and returns a SpatRaster

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

# Default: four corners and center
make_proxy(rast_grid, proxy_edf())

# Custom coordinates
custom_coords = matrix(c(50, 50, 150, 150), ncol = 2, byrow = TRUE)
rownames(custom_coords) = c("point1", "point2")
make_proxy(rast_grid, proxy_edf(coords = custom_coords))

---

Oblique Geographic Coordinates proxy factory

Description

Returns a function that generates Oblique Geographic Coordinates (OGC) as covariates.

Usage

proxy_ogc(n = 5)

Arguments

n	Number of angles (default: 5)

Value

A function that accepts rast_grid and returns a SpatRaster

References

Møller, A. B., Beuchert, A. M., Pouladi, N., & Greve, M. H. (2020). Oblique geographic coordinates as covariates for digital soil mapping. Soil, 6(2), 269-289.

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

make_proxy(rast_grid, proxy_ogc(n = 5))

---

Sample spatial field

Description

Create a sample of a spatial field.

Usage

sam_field(x, size, method = sample_random())

Arguments

x	A raster object (SpatRaster).
size	Number of samples to create.
method	Sampling method (function created by sample_random(), sample_jittered(), or sample_clustered()).

Value

An sf object with sampled points

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

sam_field(
  rast_grid,
  100,
  method = sample_jittered(amount = 5)
)

---

Clustered sampling method

Description

Returns a function that performs clustered sampling on a spatial field. Cluster centers are randomly distributed, then samples are drawn within a buffer radius around each cluster.

Usage

sample_clustered(nclusters, radius, ...)

Arguments

nclusters	Number of clusters
radius	Cluster radius (in map units)
...	Additional arguments passed to terra::spatSample()

Value

A function that accepts x (SpatRaster) and size and returns an sf object

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

sam_field(rast_grid, 200, method = sample_clustered(nclusters = 5, radius = 10))

---

Jittered sampling method

Description

Returns a function that performs jittered sampling on a spatial field. Regular points are generated first, then jittered by a random amount.

Usage

sample_jittered(amount, ...)

Arguments

amount	Jitter amount in map units
...	Additional arguments passed to terra::spatSample()

Value

A function that accepts x (SpatRaster) and size and returns an sf object

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

sam_field(rast_grid, 100, method = sample_jittered(amount = 5))

---

Random sampling method

Description

Returns a function that performs random sampling on a spatial field.

Usage

sample_random(...)

Arguments

...	Additional arguments passed to terra::spatSample()

Value

A function that accepts x (SpatRaster) and size and returns an sf object

Examples

rast_grid = terra::rast(
  ncols = 300, nrows = 100,
  xmin = 0, xmax = 300,
  ymin = 0, ymax = 100
)

sam_field(rast_grid, 100, method = sample_random())

---

Simulate a raster stack of covariates

Description

Generic function for simulating spatial covariates using a specified method.

Usage

sim_covariates(rast_grid, n = 6, method)

Arguments

rast_grid	A SpatRaster object with the desired dimensions
n	The number of covariates to simulate (must be >= 1)
method	A simulation factory function —- call the function with parameters to create the method (remember to not pass the function itself). For example: method = simulate_gaussian(range = 25), not method = simulate_gaussian. See simulate_gaussian() and simulate_random() for examples.

Value

A SpatRaster with n layers named cov1, cov2, ..., covN

Examples

rast_grid = terra::rast(ncols = 300, nrows = 100,
  xmin = 0, xmax = 300, ymin = 0, ymax = 100)
# Gaussian simulation
sf1 = sim_covariates(rast_grid, n = 4, method = simulate_gaussian(range = 25))
sf2 = sim_covariates(rast_grid, n = 4, method = simulate_gaussian(range = 50, model = "Exp"))
# Reusable simulation engine
gauss = simulate_gaussian(range = 25)
sf3 = sim_covariates(rast_grid, n = 4, method = gauss)
# Random simulation
sf4 = sim_covariates(rast_grid, n = 4, method = simulate_random())
terra::plot(sf1)
terra::plot(sf2)
terra::plot(sf3)
terra::plot(sf4)

---

Simulate Gaussian random fields

Description

Returns a function that simulates spatially correlated Gaussian random fields using a variogram model.

Usage

simulate_gaussian(
  vgm = NULL,
  psill = 1,
  model = "Sph",
  range = NULL,
  nugget = 0,
  beta = 0,
  nmax = 30,
  indicators = FALSE,
  seed = NULL
)

Arguments

vgm	A variogram model object (variogramModel or gstatVariogramModel). If NULL, one is built from model, psill, range, and nugget.
psill	Partial sill (default: 1). Ignored if vgm is provided.
model	Variogram model type (e.g., "Sph", "Exp", "Gau", "Nug"). Ignored if vgm is provided.
range	Spatial range parameter. Required if vgm is NULL.
nugget	Nugget effect (default: 0). Ignored if vgm is provided.
beta	Mean of the Gaussian field (default: 0). Passed to gstat::gstat().
nmax	The number of nearest observations used for kriging simulation (default: 30). Passed to gstat::gstat().
indicators	Indicator thresholds (default: FALSE). Passed to stats::predict(). Use TRUE for default thresholds or a numeric vector for custom thresholds.
seed	Optional random seed for reproducibility. Set this to ensure that the same random field is generated every time the returned function is called.

Value

A function that accepts rast_grid and n and returns a SpatRaster

Examples

rast_grid = terra::rast(ncols = 300, nrows = 100,
  xmin = 0, xmax = 300, ymin = 0, ymax = 100)
# Direct usage
sim_fn = simulate_gaussian(range = 25)
sf1 = sim_covariates(rast_grid, n = 4, method = sim_fn)
# With custom variogram
vgm = gstat::vgm(model = "Exp", psill = 1, range = 10)
sim_fn2 = simulate_gaussian(vgm = vgm)
sf2 = sim_covariates(rast_grid, n = 4, method = sim_fn2)
terra::plot(sf1)
terra::plot(sf2)

---

Simulate uncorrelated random fields

Description

Returns a function that simulates uncorrelated random fields (white noise).

Usage

simulate_random(mean = 0, sd = 1, seed = NULL)

Arguments

mean	Mean of the random values (default: 0)
sd	Standard deviation of the random values (default: 1)
seed	Optional random seed for reproducibility

Value

A function that accepts rast_grid and n and returns a SpatRaster

Examples

rast_grid = terra::rast(ncols = 300, nrows = 100,
  xmin = 0, xmax = 300, ymin = 0, ymax = 100)
sim_fn = simulate_random()
sf1 = sim_covariates(rast_grid, n = 4, method = sim_fn)
terra::plot(sf1)

---