This function performs thinning of spatial points by assigning them to grid cells based on a specified resolution or thinning distance. It can either create a new raster grid or use an existing `terra::SpatRaster` object.
Usage
grid_thinning(
coordinates,
thin_dist = NULL,
resolution = NULL,
origin = NULL,
raster_obj = NULL,
n = 1,
trials = 10,
all_trials = FALSE,
crs = "epsg:4326",
priority = NULL
)Arguments
- coordinates
A numeric matrix or data frame with two columns representing the x (longitude) and y (latitude) coordinates of the points.
- thin_dist
A numeric value representing the thinning distance in kilometers. It will be converted to degrees if `resolution` is not provided.
- resolution
A numeric value representing the resolution (in degrees) of the raster grid. If provided, this takes priority over `thin_dist`.
- origin
A numeric vector of length 2 (e.g., `c(0, 0)`), specifying the origin of the raster grid (optional).
- raster_obj
An optional `terra::SpatRaster` object to use for grid thinning. If provided, the raster object will be used instead of creating a new one.
- n
A positive integer specifying the maximum number of points to retain per grid cell (default: 1).
- trials
An integer specifying the number of trials to perform for thinning (default: 10).
- all_trials
A logical value indicating whether to return results for all trials (`TRUE`) or just the first trial (`FALSE`, default).
- crs
An optional CRS (Coordinate Reference System) to project the coordinates and raster (default WGS84, `epsg:4326`). This can be an EPSG code, a PROJ.4 string, or a `terra::crs` object.
- priority
A numeric vector of the same length as the number of points, specifying a priority weight for each point. Higher values indicate higher importance and are favored when selecting which points to retain. Priority is used to guide selection when multiple candidate points are otherwise equally valid (e.g., points in the same grid cell, with the same rounded coordinates, or with the same number of neighbors).
Examples
# Example: Grid thinning using thin_dist
coords <- matrix(c(-122.4194, 37.7749,
-122.4195, 37.7740,
-122.4196, 37.7741), ncol = 2, byrow = TRUE)
result <- grid_thinning(coords, thin_dist = 10, trials = 5, all_trials = TRUE)
print(result)
#> [[1]]
#> [1] TRUE TRUE FALSE
#>
#> [[2]]
#> [1] TRUE TRUE FALSE
#>
#> [[3]]
#> [1] FALSE TRUE TRUE
#>
#> [[4]]
#> [1] FALSE TRUE TRUE
#>
#> [[5]]
#> [1] FALSE TRUE TRUE
#>
# Example: Grid thinning using a custom resolution
result_res <- grid_thinning(coords, resolution = 0.01, n = 2, trials = 5)
print(result_res)
#> [[1]]
#> [1] TRUE TRUE TRUE
#>
# Example: Using a custom raster object
library(terra)
#> terra 1.8.54
rast_obj <- terra::rast(nrows = 100, ncols = 100, xmin = -123, xmax = -121, ymin = 36, ymax = 38)
result_raster <- grid_thinning(coords, raster_obj = rast_obj, trials = 5)
print(result_raster)
#> [[1]]
#> [1] FALSE TRUE FALSE
#>