Estimate the size of a rerddap::griddap() request

Uses coordinate metadata from an ERDDAP info() object to estimate how many grid cells will be returned and the total uncompressed byte count for each requested data variable. No network request is made.

estimate_griddap_size(
  info,
  ...,
  fields = "all",
  stride = 1L,
  spacing = list(),
  verbose = TRUE
)

Arguments

info

An object returned by rerddap::info().

...

Named dimension constraints, one per coordinate variable to constrain. Names must exactly match the coordinate variable names in the dataset (as returned by dimvars(info)). Each value is c(min, max); for time use ISO 8601 strings.

fields

Character vector of data variable names, or "all" (default).

stride

Integer scalar or named list of per-dimension stride values, using the same convention as griddap(). Default 1.

spacing

Optional named list to override auto-detected spacing for one or more dimensions. For time, supply seconds as time_sec (e.g. spacing = list(time_sec = 86400)). For other dimensions use the coordinate variable name (e.g. spacing = list(latitude = 0.01, xi_rho = 1)).

verbose

Logical; print a formatted summary (default TRUE).

Value

Invisibly, a named list containing per-dimension point counts, spacing values, per-variable byte estimates, and total bytes.

Details

Coordinate dimension names are taken directly from the info object using the same logic as rerddap:::dimvars() — the set-difference between all keys in info$alldata and the data variable names plus "NC_GLOBAL". This means any coordinate system works: geographic lat/lon, projected x/y, sigma-layer depth, ROMS xi_rho/eta_rho, etc.

Dimension constraints are passed via ... using the exact coordinate variable names reported by the dataset, the same way griddap() accepts them. Each constraint is a numeric (or character for time) vector of length 2: c(min, max).

Spacing is resolved in this order for each dimension:

  1. User-supplied override in the spacing argument.

  2. For time: (t_max - t_min) / (nValues - 1) derived from the dimension's nValues row and actual_range attribute. This correctly handles running composites where time steps are daily even though the composite window is e.g. 8 days.

  3. NC_GLOBAL attributes: geospatial_lat_resolution, geospatial_lon_resolution, time_coverage_resolution (ISO 8601).

  4. Coordinate variable attributes: point_spacing, resolution, spacing.

  5. For time: averageSpacing string from the nValues row as a last resort.

  6. If the constraint min == max the dimension contributes 1 point.

  7. Otherwise: NA — a warning is issued and 1 point is assumed.

Examples

if (FALSE) { # \dontrun{
  library(rerddap)

  myURL <- "https://coastwatch.pfeg.noaa.gov/erddap/"
  response <- try(httr::HEAD(myURL, httr::timeout(10)), silent = TRUE)
  if (inherits(response, "try-error")) {
     stop("The ERDDAP\u2122 server is not responding")
  }
  info <- rerddap::info("erdMH1chla8day", url = myURL)
  estimate_griddap_size(info,
    latitude  = c(30, 50),
    longitude = c(-140, -110),
    time      = c("2020-01-01", "2020-12-31"))
} # }