auto_BAUs function

Automatic BAU generation

This function calls the generic function auto_BAU (not exported) after a series of checks and is the easiest way to generate a set of Basic Areal Units (BAUs) on the manifold being used; see details.

auto_BAUs(
  manifold,
  type = NULL,
  cellsize = NULL,
  isea3h_res = NULL,
  data = NULL,
  nonconvex_hull = TRUE,
  convex = -0.05,
  tunit = NULL,
  xlims = NULL,
  ylims = NULL,
  spatial_BAUs = NULL,
  ...
)

Arguments

• manifold: object of class manifold
• type: either grid'' or hex'', indicating whether gridded or hexagonal BAUs should be used. If type is unspecified, hex'' will be used if we are on the sphere, and grid'' will used otherwise
• cellsize: denotes size of gridcell when type = ``grid''. Needs to be of length 1 (square-grid case) or a vector of length dimensions(manifold) (rectangular-grid case)
• isea3h_res: resolution number of the isea3h DGGRID cells for when type is ``hex'' and manifold is the surface of a sphere
• data: object of class SpatialPointsDataFrame, SpatialPolygonsDataFrame, STIDF, or STFDF. Provision of data implies that the domain is bounded, and is thus necessary when the manifold is a real_line, plane, or STplane, but is not necessary when the manifold is the surface of a sphere
• nonconvex_hull: flag indicating whether to use fmesher to generate a non-convex hull. Otherwise a convex hull is used
• convex: convex parameter used for smoothing an extended boundary when working on a bounded domain (that is, when the object data is supplied); see details
• tunit: temporal unit when requiring space-time BAUs. Can be "secs", "mins", "hours", etc.
• xlims: limits of the horizontal axis (overrides automatic selection)
• ylims: limits of the vertical axis (overrides automatic selection)
• spatial_BAUs: object of class SpatialPolygonsDataFrame or SpatialPixelsDataFrame representing the spatial BAUs to be used in a spatio-temporal setting (if left NULL, the spatial BAUs are constructed automatically using the data)
• ...: currently unused

Details

auto_BAUs constructs a set of Basic Areal Units (BAUs) used both for data pre-processing and for prediction. As such, the BAUs need to be of sufficienly fine resolution so that inferences are not affected due to binning.

Two types of BAUs are supported by FRK: hex'' (hexagonal) and grid'' (rectangular). In order to have a grid'' set of BAUs, the user should specify a cellsize of length one, or of length equal to the dimensions of the manifold, that is, of length 1 for `real_line` and of length 2 for the surface of a `sphere` and `plane`. When a hex'' set of BAUs is desired, the first element of cellsize is used to determine the side length by dividing this value by approximately 2. The argument type is ignored with real_line and ``hex'' is not available for this manifold.

If the object data is provided, then automatic domain selection may be carried out by employing the fmesher function fm_nonconvex_hull_inla, which finds a (non-convex) hull surrounding the data points (or centroids of the data polygons). This domain is extended and smoothed using the parameter convex. The parameter convex should be negative, and a larger absolute value for convex results in a larger domain with smoother boundaries.

Examples

## First a 1D example
library(sp)
set.seed(1)
data <- data.frame(x = runif(10)*10, y = 0, z= runif(10)*10)
coordinates(data) <- ~x+y
Grid1D_df <- auto_BAUs(manifold = real_line(),
                       cellsize = 1,
                       data=data)
## Not run: spplot(Grid1D_df)
## Now a 2D example
data(meuse)
coordinates(meuse) = ~x+y # change into an sp object

## Grid BAUs
GridPols_df <- auto_BAUs(manifold = plane(),
                         cellsize = 200,
                         type = "grid",
                         data = meuse,
                         nonconvex_hull = 0)
## Not run: plot(GridPols_df)
## Hex BAUs
HexPols_df <- auto_BAUs(manifold = plane(),
                        cellsize = 200,
                        type = "hex",
                        data = meuse,
                        nonconvex_hull = 0)
## Not run: plot(HexPols_df)

See Also

auto_basis for automatically constructing basis functions.