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Parallel‑Transect Quadrat Placement

Source: R/quadrats_transect.R
place_quadrats_transect.Rd

Places axis‑aligned rectangular quadrats at evenly spaced positions along a set of parallel transect lines crossing the domain at a specified compass angle. The function first shrinks the domain by half the quadrat diagonal to form a safe sampling area, ensuring that every returned quadrat lies fully inside the original domain.

Usage

place_quadrats_transect(
  domain,
  n_transects,
  n_quadrats_per_transect,
  quadrat_size,
  angle
)

Arguments

domain

An sf polygon/multipolygon defining the sampling region. Must carry a valid projected CRS suitable for linear units (e.g., meters).

n_transects

Integer (≥1). Number of parallel transect lines to generate.

n_quadrats_per_transect

Integer (≥1). Number of quadrats to place along each transect after clipping to the safe area.

quadrat_size

Numeric vector of length 2, c(width, height), giving quadrat dimensions in the same units as the domain CRS. Both values must be positive and finite.

angle

Numeric. Compass bearing in degrees for transect orientation (0 = North/up, 90 = East/right). Values outside [0, 360) are allowed and are interpreted modulo 360.

Value

An sf object (polygons) with:

quadrat_id

Sequential integer identifier for each placed quadrat.

geometry

Axis‑aligned rectangular polygon for the quadrat.

Details

  • The transect orientation is given by angle in compass degrees (0 = North, 90 = East, 180 = South, 270 = West).

  • n_transects parallel lines are positioned across the domain’s extent, then each line is cropped to the safe area. Along each retained segment, n_quadrats_per_transect centers are placed by linear interpolation from segment start to end (a single quadrat uses the midpoint).

  • Each center generates an axis‑aligned rectangular quadrat of size quadrat_size = c(width, height) in the domain’s units.

  • Use a projected (planar) CRS for domain (e.g., meters) so that distances and sizes are meaningful. If the domain is too small relative to quadrat_size, the safe area may be empty and no quadrats are returned.

See also

place_quadrats (random, non‑overlapping), place_quadrats_systematic (regular grid over bounding box), place_quadrats_tiled (systematic tiling by cell size), place_quadrats_voronoi (Voronoi‑based centers)

Examples