Compute interpolation weights for geographic transformations

For repeated transformations from the same grid definition, it may be more efficient to compute the interpolation weights first and then compute the transformations with those weights. These functions are used to compute the interpolation weights, which can then be passed to the geo_transform function via the opts argument, or to an explicit geo_<transformation> function via the weights argument

Usage

geo_weights(x, trans = c("points", "regrid", "xsection"), opts)

geo_weights_points(
  x,
  points,
  method = c("bilinear", "nearest", "bicubic"),
  mask = NULL,
  force = FALSE
)

geo_weights_regrid(
  x,
  new_grid,
  method = c("bilinear", "nearest", "bicubic"),
  mask = NULL,
  new_mask = NULL
)

geo_weights_xsection(
  x,
  p1,
  p2,
  n = 100,
  method = c("bilinear", "nearest", "bicubic")
)

Arguments

x: A geofield, geolist, or a data frame with class harp_grid_df. For transformations that do not involve the interpolation of gridded data (e.g. zoom, subgrid) x can also be a geodomain.
trans: The transformation to apply. Can be "points", "regrid", "xsection", "subgrid", or "zoom".
opts: A list of options for the chosen transformation. The appropriate geo_opts function should be used to generate this list.
points: A data frame of geographic points to which to interpolate the gridded data. The data frame must include the columns "SID" for a unique id for the point, "lon" for the longitude of the point in decimal degrees and "lat" for the latitude of the point in decimal degrees. The data frame can contain other columns, which will be retained in the output.
method: The interpolation method. Can be "nearest" for nearest neighbour, "bilinear", or "bicubic." The default is "bilinear". For geo_upscale, can be any function that summarises a vector to a single value and can found with match.fun, the default being "mean". A further option is "downsample", dwhich is described in the argument for downsample_location.
mask: A mask to prevent grid points being used in the interpolation. Should be on the same grid as x and grid points with values of 0 or FALSE will be masked from the interpolation.
force: For interpolations that include a mask, it is possible that a point will be surrounded by 4 masked points. In this case the mask will be ignored and all 4 points used in the interpolation (the default). Set force = TRUE to force the mask to be applied and set the interpolated to NA.
new_grid: A geofield or geodomain on the grid that x should be regridded to. define_domain can be used to define a new geodomain.
new_mask: A geofield on the same grid as new_grid with grid points that should not be interpolated to set to 0 or FALSE.
p1: The geographic location in decimal degrees of the start of the section. Should be a vector of length 2 with the first value being the longitude and the second value the latitude.
p2: The geographic location in decimal degrees of the end of the section. Should be a vector of length 2 with the first value being the longitude and the second value the latitude.
n: The number of equally spaced points along the section. The default is 100.

Value

The interpolation weights for the geographic transformation.