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Suggest Reasonable Variogram Default Parameters

gc_vgm_defaults.Rd

Inspect data extent and ILR covariance structure to suggest ballpark values for range, nugget, and sill of a variogram model. This is a convenience function to help users get started before fine-tuning.

Usage

gc_vgm_defaults(ilr_params, extent)

Arguments

ilr_params

A list returned by gc_ilr_params().

extent

A numeric vector of length 4: c(xmin, ymin, xmax, ymax), or a spatial object (sf, terra) from which extent can be extracted.

Value

A list containing:

  • range: Suggested range parameter (approximately 1/3 of the diagonal extent)

  • nugget: Suggested nugget ratio (typically 0.01 to 0.05 of average sill)

  • mean_sill: Mean of the diagonal covariance terms

Details

This function:

  1. Calculates the spatial extent diagonal (Euclidean distance from min to max)

  2. Suggests range as ~1/3 of the extent diagonal

  3. Calculates mean of diagonal covariance terms as representative sill

  4. Suggests nugget as 1% of the mean sill

These are heuristics and should be refined using empirical variography (see gc_fit_vgm()).

Examples

samples <- data.frame(
  sand = c(20, 25, 30, 22),
  silt = c(60, 55, 50, 58),
  clay = c(20, 20, 20, 20)
)

params <- gc_ilr_params(samples)
extent <- c(0, 0, 100, 100)

suggestions <- gc_vgm_defaults(params, extent)
print(suggestions)
#> $range
#> [1] 47.14045
#> 
#> $nugget
#> [1] 0.0001699233
#> 
#> $mean_sill
#> [1] 0.01699233
#>