#
# fields  is a package for analysis of spatial data written for
# the R software environment.
# Copyright (C) 2021 Colorado School of Mines
# 1500 Illinois St., Golden, CO 80401
# Contact: Douglas Nychka,  douglasnychka@gmail.edu,
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with the R software environment if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
# or see http://www.r-project.org/Licenses/GPL-2
##END HEADER
"fields.x.to.grid" <- function(x, nx = 80, ny = 80, xy = c(1, 2)) {
  if (is.null(x)) {
    stop("Need a an x matrix to determine ranges for grid")
  }
  M <- ncol(x)
  if (M == 1) {
    #special case of 1-D
    grid.list <-  list(x = seq(min(x), max(x), length.out = nx))
    
  }
  else{
    grid.list <- as.list(1:M)
    # add columns names
    names(grid.list) <- dimnames(x)[[2]]
    #     cruise through x dimensions and find medians.
    for (k in 1:M) {
      grid.list[[k]] <- median(x[, k])
    }
    #
    #
    # overwrite with sequences for the two variables of surface
    xr <- range(x[, xy[1]])
    yr <- range(x[, xy[2]])
    grid.list[[xy[1]]] <- seq(xr[1], xr[2], , nx)
    grid.list[[xy[2]]] <- seq(yr[1], yr[2], , ny)
  }
    return(grid.list)
}
