# fields, Tools for spatial data
# Copyright 2004-2011, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"discretize.image" <- function(x, m = 64, n = 64, 
    grid = NULL, expand = c(1, 1), boundary.grid = FALSE) {
    #
    # set up discretized grid based on x
    #
    out <- list()
    if (length(expand) == 1) 
        expand <- rep(expand, 2)
    if (is.null(grid)) {
        grid <- list()
        xr <- range(x[, 1])
        deltemp <- (xr[2] - xr[1]) * (expand[1] - 1) * 0.5
        grid$x <- seq(xr[1] - deltemp, xr[2] + deltemp, , m)
        yr <- range(x[, 2])
        deltemp <- (yr[2] - yr[1]) * (expand[2] - 1) * 0.5
        grid$y <- seq(yr[1] - deltemp, yr[2] + deltemp, , n)
    }
    # find cut points for boundaries assuming midpoints
    if (!boundary.grid) {
        xcut <- fields.convert.grid(grid$x)
        ycut <- fields.convert.grid(grid$y)
    }
    else {
        # cut points given boundaries
        xcut <- grid$x
        ycut <- grid$y
    }
    # locate bin ids for each location
    out$index <- cbind(cut(x[, 1], xcut), cut(x[, 2], ycut))
    out$m <- length(xcut) - 1
    out$n <- length(ycut) - 1
    out$grid <- grid
    if (!boundary.grid) {
        #discretized locations
        out$loc <- cbind(grid$x[out$index[, 1]], grid$y[out$index[, 
            2]])
    }
    else {
        out$loc <- NA
    }
    out
}