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Sample rasters along transects

Source: R/transects.R
sample_transects.Rd

Extracts raster values along transect lines at regular distances.

Usage

sample_transects(
  transects,
  x,
  spacing = NULL,
  n = NULL,
  method = "bilinear",
  drop_na = FALSE
)

extract_cross_sections(
  transects,
  x,
  spacing = NULL,
  n = NULL,
  method = "bilinear"
)

Arguments

transects

Line geometry from make_transects() or another source.

x

A terra::SpatRaster or local raster path. Multi-layer rasters are accepted when sampling bathymetry together with derived terrain metrics.

spacing

Optional sample spacing in map units.

n

Optional number of sample points per transect.

method

Extraction method passed to terra::extract().

drop_na

Logical. If TRUE, remove sample rows where all raster value columns are missing.

Value

A tibble with transect identifiers, distances, coordinates, and raster values.

Details

If spacing and n are both NULL, twenty points are sampled per transect. Distances are measured from the first line vertex and are in map units. Transect attribute columns, including orientation metadata created by make_transects(), are preserved in the sampled table.

See also

make_transects(), summarize_cross_sections()

Examples

bathy <- read_bathy(blueterra_example("bathy"))
zones <- terra::vect(blueterra_example("zones"))
transects <- make_transects(zones[1, ], spacing = 100, bathy = bathy)
sample_transects(transects, bathy, n = 5)
#> # A tibble: 15 × 19
#>    site_id site_name feature_type source_name width_m height_m angle_deg zone_id
#>    <chr>   <chr>     <chr>        <chr>         <dbl>    <dbl>     <dbl> <chr>  
#>  1 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  2 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  3 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  4 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  5 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  6 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  7 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  8 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#>  9 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 10 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 11 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 12 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 13 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 14 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> 15 hitw    Hole-in-… sampling_re… Hole In th…     300      300      94.3 1      
#> # ℹ 11 more variables: offset <dbl>, angle_source <chr>, mean_aspect_deg <dbl>,
#> #   orientation_weight <chr>, n_orientation_cells <int>,
#> #   orientation_resultant_length <dbl>, transect_id <chr>, distance <dbl>,
#> #   x <dbl>, y <dbl>, bathy_m <dbl>