Estimate mean surface orientation from a bathymetric raster

Estimates the mean aspect direction of a raster surface and converts that compass bearing to the line-angle convention used by make_transects().

Usage

estimate_surface_orientation(
  bathy,
  area = NULL,
  orientation_weight = c("slope", "none"),
  min_slope = 0,
  return = c("transect_angle", "bearing", "both")
)

Arguments

bathy

A single-layer bathymetric or elevation raster, or a raster input accepted by as_bathy().

area

Optional polygon area used to crop and mask bathy before estimating orientation.

orientation_weight

Weighting method. "slope" weights aspect components by slope magnitude; "none" averages finite aspect cells equally.

min_slope

Minimum slope in degrees retained when orientation_weight = "slope".

return

Return type: "transect_angle" for the mathematical line angle used by make_transects(), "bearing" for the mean compass aspect, or "both" for a tibble containing both values and the number of cells used.

Value

A numeric angle for "transect_angle" or "bearing", or a tibble with bearing_deg, transect_angle_deg, orientation_weight, min_slope, and n_orientation_cells when return = "both".

Details

Aspect is treated as a compass bearing where northness is cos(aspect) and eastness is sin(aspect). Mean circular components are converted to a compass bearing with atan2(eastness, northness). Transect lines are undirected, so the line angle is normalized to [0, 180). A south-facing mean aspect near 180 degrees therefore produces a transect angle near 90 degrees.

See also

make_transects(), derive_aspect(), derive_slope()

Examples

bathy <- read_bathy(blueterra_example("hitw"))
zones <- terra::vect(blueterra_example("zones"))
hitw <- zones[zones$site_id == "hitw", ]
estimate_surface_orientation(bathy, hitw)
#> [1] 94.69969