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Derive a custom metric from raster layers

Source: R/custom-metrics.R
derive_custom_metric.Rd

Creates a single custom metric layer from an expression or a user-supplied R function.

Usage

derive_custom_metric(
  metrics,
  name,
  expression = NULL,
  fun = NULL,
  ...,
  overwrite = FALSE
)

Arguments

metrics

A terra::SpatRaster metric stack.

name

Output layer name.

expression

Optional quoted R expression evaluated with raster layers available by name.

fun

Optional function called as fun(metrics, ...). The function must return a single-layer terra::SpatRaster.

...

Additional arguments passed to fun.

overwrite

Logical. Allow name to match an existing layer in metrics.

Value

A single-layer terra::SpatRaster named name.

Details

Expressions must be quoted, for example quote(slope_deg * rugosity_vrm_3x3). Character strings are not evaluated. This keeps the workflow explicit and avoids treating text as code.

See also

add_metric_layers()

Examples

bathy <- read_bathy(blueterra_example("bathy"))
metrics <- derive_terrain(bathy, metrics = c("slope", "tri", "bpi"))
derive_custom_metric(metrics, "slope_tri_index", expression = quote(slope_deg * tri))
#> class       : SpatRaster
#> size        : 90, 190, 1  (nrow, ncol, nlyr)
#> resolution  : 19.98372, 19.98372  (x, y)
#> extent      : 134960.3, 138757.2, 204151.7, 205950.2  (xmin, xmax, ymin, ymax)
#> coord. ref. : NAD83 / Puerto Rico & Virgin Is. (EPSG:32161)
#> source(s)   : memory
#> varname     : laparguera_slope_bathy
#> name        : slope_tri_index
#> min value   :        0.007697
#> max value   :     3577.811514

relief <- derive_custom_metric(metrics, "relief_index", fun = function(r) {
  out <- r[["tri"]] + abs(r[["bpi_3x3"]])
  names(out) <- "relief_index"
  out
})
relief
#> class       : SpatRaster
#> size        : 90, 190, 1  (nrow, ncol, nlyr)
#> resolution  : 19.98372, 19.98372  (x, y)
#> extent      : 134960.3, 138757.2, 204151.7, 205950.2  (xmin, xmax, ymin, ymax)
#> coord. ref. : NAD83 / Puerto Rico & Virgin Is. (EPSG:32161)
#> source(s)   : memory
#> varname     : laparguera_slope_bathy
#> name        : relief_index
#> min value   :     0.155394
#> max value   :    72.388597