strata: Create Stratification Units

In rassta: Raster-Based Spatial Stratification Algorithms

Create Stratification Units

Description

Stratification units are created from the spatial intersection of raster layers representing different sets of classification units. Each set of classification units is related to a particular landscape factor (e.g., topography, climate) or to a particular spatial scale for a single landscape factor (e.g., micro-climate, macro-topography). Each resulting stratification unit is considered to represent a distinct landscape configuration in terms of multiple landscape factors/factor scales (represented by the classification units). This function automatically assigns a unique numeric code to each stratification unit. For x stratification unit, the numeric code represents the unique combination of classification units whose spatial intersection resulted in x. See Examples to get a better idea of the logic behind the code assignment process.

Usage

strata(cu.rast, to.disk = FALSE, outdir = ".", su.name, ...)

Arguments

cu.rast	SpatRaster, as in rast. Multi-layer SpatRaster for which each layer represents a set of classification units for a particular landscape factor or factor scale. Integer cell values (i.e., numeric identifiers) are expected.
to.disk	Boolean. Write the resulting raster layer of stratification units to disk? Default: FALSE
outdir	Character. If to.disk = TRUE, string specifying the path for the output raster layer of stratification units. Default: "."
su.name	Character. If to.disk = TRUE, file name (including extension) for the output raster layer of stratification units.
...	Additional arguments as for writeRaster.

Details

When printing su.rast$code.mult, the output shows the multiplier used for each landscape factor/factor scale. From this output, one can manually replicate the creation of stratification units through simple raster algebra. To do so, a weighted sum of the SpatRasters containing the classification units for each landscape factor/factor scale should be performed using the multipliers as weights. Note that the weights do not imply relative importance. The weights are required only to preserve a logical structure of the landscape factors/factor scales in the resulting numeric code.

Value

su.rast: Single-layer SpatRaster representing the stratification units occurring across geographic space. The cell values in this raster layer represents the numeric codes of stratification units.

code.mult: Multipliers used for the creation of the numeric codes. See Details.

See Also

Other Functions for Landscape Stratification: som_gap(), som_pam()

Examples

require(terra)
p <- system.file("exdat", package = "rassta")
# Multi-layer SpatRast with classification units (Cus)
## Three sets (i.e., landscape factors): geology, climate and topography
fcu <- list.files(path = p,
                  pattern = "geology.tif|climate.tif|topography.tif",
                  full.names = TRUE
                 )
cu <- terra::rast(fcu)
# Stratification units (SUs)
su <- strata(cu.rast = cu)
# Plot the stratification units
if(interactive()){plot(su$su.rast, type = "classes")}
#
# Note code structure from SUs and corresponding values from CUs
z <- c(su$su.rast, cu)[46,61]   # Example of one cell (row = 45, column = 45)
su$code.mult                    # Multipliers
z[c("SU", names(su$code.mult))] # Code structure

# Note what happens when some landscape factors have cell values greater...
#... than 1 digit (i.e., more than 9 distinct classification units)
cu <- c(cu[[1]], cu[[2]]^4, cu[[3]]^2)
su <- strata(cu.rast = cu)
su$code.mult
c(su$su.rast, cu[[names(su$code.mult)]])[46,61]

rassta documentation built on Sept. 11, 2024, 6:33 p.m.