R/makeGrid.R

In thibautjombart/geograph: Walking through the geographic space using graphs

############
## makeGrid
############


#' Build a regular grid gGraph
#'
#' The function \code{makeGrid} builds a \linkS4class{gGraph} using a regular
#' grid for a given area. If no area is specified, currently plotted area is
#' used. Note that such grid is only valid for small scales, for cases in which
#' curvature of the surface of the earth can be neglected.
#'
#'
#' @param size an integer giving the approximate number of nodes of the grid.
#' The function will attempt to make a square grid of (approximately) this
#' size.
#' @param n.lon the number of longitude coordinates of the grid (i.e., width of
#' the grid, in number of cells)
#' @param n.lat the number of latitude coordinates of the grid (i.e., height of
#' the grid, in number of cells)
#' @param lon.range,lat.range vectors of length two giving the range covered by
#' the grid, in longitude and latitude, respectively.
#' @return A \linkS4class{gGraph} object.

#' @keywords utilities methods
#' @export
#' @examples
#'
#' ## zoom in to a smaller area
#' plot(worldgraph.10k)
#' geo.zoomin(c(-10, 0, 50, 54))
#'
#'
#' ## make a new gGraph
#' newGraph <- makeGrid(1e3)
#' newGraph <- findLand(newGraph)
#' newGraph@meta$colors <- data.frame(
#'   habitat = c("sea", "land"),
#'   color = c("blue", "green")
#' )
#'
#'
#' ## plot the new gGraph
#' plot(newGraph, reset = TRUE, edge = TRUE)
#'
makeGrid <- function(size = NULL, n.lon = NULL, n.lat = NULL, lon.range = NULL, lat.range = NULL) {
  ## HANDLE ARGUMENTS ##
  if (is.null(n.lon)) {
    if (is.null(size)) stop("Please provide either size or n.lon/n.lat")
    n.lon <- round(sqrt(size))
  }

  if (is.null(n.lat)) {
    if (is.null(size)) stop("Please provide either size or n.lon/n.lat")
    n.lat <- round(sqrt(size))
  }

  if (is.null(size)) {
    if (is.null(n.lon) | is.null(n.lat)) stop("Please provide either size or n.lon/n.lat")
  }

  size <- n.lon * n.lat
  if (size < 4.1) {
    size <- 4
    warning("Minimum grid size is 4 - ignoring required size.")
  }


  ## GET LON/LAT FROM ZOOM LOG ##
  ## get zoom log info
  # geoEnv <- get(".geoGraphEnv", envir=.GlobalEnv)
  zoomLog <- get("zoom.log", envir = .geoGraphEnv)
  if (nrow(zoomLog) < 1) {
    curZoom <- c(-180, 180, -90, 90)
  } else {
    curZoom <- zoomLog[1, ]
  }

  if (is.null(lon.range)) {
    lon.range <- curZoom[1:2]
  }

  if (is.null(lat.range)) {
    lat.range <- curZoom[3:4]
  }

  lon.range <- sort(lon.range)
  lat.range <- sort(lat.range)


  ## CORRECT LON/LAT ##
  if (lon.range[1] < -180) {
    lon.range[1] <- -180
    warning("Setting lowest longitude to -180 (i.e. 180 W)")
  }

  if (lon.range[2] > 180) {
    lon.range[2] <- 180
    warning("Setting largest longitude to 180 (i.e. 180 E)")
  }

  if (lat.range[1] < -90) {
    lat.range[1] <- -90
    warning("Setting lowest latitude to -90 (i.e. 90 S)")
  }

  if (lat.range[2] > 90) {
    lat.range[2] <- 90
    warning("Setting largest latitude to 90 (i.e. 90 N)")
  }


  ## BUILD GRID AND FROM/TO MATRIX ##
  x.vec <- seq(lon.range[1], lon.range[2], length = n.lon)
  y.vec <- seq(lat.range[2], lat.range[1], length = n.lat)
  x <- rep(x.vec, each = n.lat)
  y <- rep(y.vec, n.lon)
  xy <- cbind(x, y)
  colnames(xy) <- c("x", "y")


  ## lateral connections
  from <- 1:(size - n.lat)
  to <- n.lat + (1:(size - n.lat))

  ## vertical connections
  temp <- setdiff(1:(size - 1), seq(n.lat, size, length = n.lon))
  from <- c(from, temp)
  to <- c(to, temp + 1)
  ft <- cbind(from, to)

  ## CREATE graphNEL ##
  myGraph <- ftM2graphNEL(ft, V = as.character(1:size), edgemode = "undirected")


  ## CREATE gGraph ##
  res <- new("gGraph", coords = xy, graph = myGraph)

  return(res)
} # end makeGrid