R/make.soapgrid.R

In dsm: Density Surface Modelling of Distance Sampling Data

#' Create a knot grid for the internal part of a soap film smoother.
#'
#' This routine simply creates a grid of knots (in the correct format) to be
#' used as in the "internal" part of the soap film smoother
#'
#' @param bnd `list` with elements `x` and `y` which give the locations of the
#' boundary vertices. The first and last elements should be the same.
#' @param n.grid either one number giving the number of points along the `x`
#' and `y` axes that should be used to create the grid, or a vector giving the
#' number in the `x` direction, then `y` direction.
#'
#' @return a list with elements `x` and `y`, containing the knot locations.
#'
#' @author David L Miller
#' @export
make.soapgrid <- function(bnd, n.grid){
  # set the grid size, if the input is a 2-vec then it is m and n
  if(length(n.grid)==2){
     m <- n.grid[1]
     n <- n.grid[2]
  }else{
     m <- n <- n.grid
  }

  # min and max values of the boundary (but not on the boundary)
  xmin <- min(bnd$x, na.rm=TRUE)
  ymin <- min(bnd$y, na.rm=TRUE)
  xmax <- max(bnd$x, na.rm=TRUE)
  ymax <- max(bnd$y, na.rm=TRUE)

  # create the grid
  ng <- expand.grid(x=seq(xmin, xmax, length=m),
                    y=seq(ymin, ymax, length=n))

  # which bits of the grid were inSide?
  x <- ng$x; y <- ng$y
  onoff<-inSide(as.list(bnd), x, y)

  # remove the outside ones
  ng<-ng[onoff, ]

  return(ng)
}