Places axis‑aligned rectangular quadrats at the centers of a regular grid spanning the domain’s bounding box, and retains only those quadrats whose full geometry lies inside the domain polygon. The grid density is chosen to approximate n_quadrats total placements by respecting the domain’s aspect ratio (so cells are roughly square in map space while matching the requested count).
Arguments
- domain
An sf polygon/multipolygon representing the sampling region. Must carry a valid projected CRS suitable for linear measurements.
- n_quadrats
Integer (≥1). Approximate number of quadrats to place. The actual number returned is the count of grid‑centered quadrats that fully fit inside domain.
- quadrat_size
Numeric vector of length 2, c(width, height), giving the quadrat dimensions in the same linear units as domain (e.g., meters). Both values must be positive and finite.
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 grid is defined over the domain’s bounding box using nx × ny grid centers, where nx ≈ sqrt(n_quadrats / aspect_ratio) and ny ≈ aspect_ratio × nx, with aspect_ratio = height / width of the bounding box. This produces roughly nx * ny ≈ n_quadrats centers.
For each grid center, an axis‑aligned rectangle of size quadrat_size = c(width, height) is created. Quadrats are kept only if they are fully within the domain (using sf::st_within()).
If the domain is very irregular or narrow, the number of retained quadrats can be less than n_quadrats. The function returns all valid quadrats and emits a warning if none fit.
The domain should use a projected (planar) CRS so that distances and sizes are in linear units (e.g., meters). If using lon/lat, reproject first (e.g., to UTM).
See also
place_quadrats (random, non‑overlapping),
place_quadrats_tiled (systematic tiling by cell size),
place_quadrats_transect (parallel transects),
place_quadrats_voronoi (Voronoi‑based centers)