Extract gridded values at station or reference points — tbl_from

Extract values from a raster layer, stack or brick at reference point locations and return a wide table with one column per point. This prepares gridded or simulated data for point-based validation against station observations.

Usage

tbl_from_references(raster_file, ref_points, prefix_colname = NULL, ...)

Arguments

raster_file: Raster object accepted by input_raster.
ref_points: Reference point locations. This input can be a data.frame-like table with NAME, LAT and LON columns, a .txt or .csv file path, an sf object, a SpatVector object or a vector file path accepted by input_vector.
prefix_colname: If not null, a character string used to prefix the station column names.
...: further arguments passed to extract. These arguments concern only extracting the data in the rasters.

Value

A data.frame with one row per raster layer and one column per reference point.

Details

This function does not calculate validation metrics. Instead, it prepares the extracted raster values in a table shape that can be combined with observed station data and then passed to validation tools such as hydroGOF::gof(), hydroGOF::ggof() or any other function that compares observed and simulated series.

The returned table has one row per raster layer and one column per reference point. Column names are taken from the NAME field in ref_points, optionally prefixed with prefix_colname. When combining this output with observed data, make sure raster layers and observation rows represent the same dates or time steps in the same order.

Additional arguments passed through ... are forwarded to extract, allowing options such as method, buffer and fun.

Examples

raster_layer <- terra::rast(
  nrows = 2,
  ncols = 2,
  vals = 1:4,
  crs = "EPSG:4326",
  extent = c(-1, 1, -1, 1)
)
raster_stack <- c(raster_layer, raster_layer + 10)

stations <- data.frame(
  NAME = c("station_a", "station_b"),
  LAT = c(-0.5, 0.5),
  LON = c(-0.5, 0.5)
)

simulated <- tbl_from_references(
  raster_file = raster_stack,
  ref_points = stations,
  prefix_colname = "sim"
)

simulated
#>   sim_station_a sim_station_b
#> 1             3             2
#> 2            13            12