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Flag grid nodes covered by the hauls of each year

Source: R/utility.R
add_grid_support.Rd

Adds two columns to a prediction grid from make_survey_grid() that show where the survey actually sampled: supported, whether the hauls of a year (and its neighbouring years) cover a node, and coverage, the share of years in which a node is covered. Predictions in nodes without support are extrapolations.

Usage

add_grid_support(
  grid,
  x,
  y,
  time,
  max_dist,
  fill_gaps = NULL,
  window = 1,
  resolution = NULL
)

Arguments

grid

A data frame with columns X and Y on a regular grid, and optionally year, e.g. from make_survey_grid().

x, y

Numeric vectors of haul coordinates, in the units of the grid.

time

Vector of haul years, the same length as x.

max_dist, fill_gaps

Distances as in make_survey_grid().

window

Non-negative number. A node is supported in a year when hauls from years at most window away cover it. Default 1: the year itself and the years before and after.

resolution

Grid spacing. If NULL (default), taken from the spacing of grid.

Value

grid with the columns supported (logical; only when grid has a year column, otherwise coverage by all hauls) and coverage (numeric between 0 and 1) added.

Details

A node is covered by a set of hauls when it lies within max_dist of one of them, after filling gaps with fill_gaps, exactly as in make_survey_grid().

coverage is computed per node from the hauls of each year alone, without window. The years counted are those in grid$year when the grid has a year column, so that years without hauls count as not covered, and those in time otherwise. A threshold such as coverage >= 0.25 keeps the nodes the survey covers regularly.

Surveys sampled in several quarters usually cover different areas in each. Run the function per quarter, with the hauls of that quarter (see the examples).

See also

make_survey_grid()

Examples

if (requireNamespace("RANN", quietly = TRUE)) {
  hh <- dab[["HH"]]
  hh <- hh[!is.na(hh$lon) & !is.na(hh$lat), ]
  years <- as.numeric(as.character(hh$Year))
  grid <- make_survey_grid(hh$lon, hh$lat, resolution = 0.2,
                           max_dist = 0.3, time = sort(unique(years)))

  ## One quarter
  q1 <- hh$Quarter == "1"
  g1 <- add_grid_support(grid, hh$lon[q1], hh$lat[q1], years[q1],
                         max_dist = 0.3)
  table(g1$supported, g1$year)

  ## Nodes covered in at least a quarter of the years
  core <- g1[g1$coverage >= 0.25, ]
}