#
#    as.im.R
#
#    conversion to class "im"
#
#    $Revision: 1.26 $   $Date: 2009/08/21 19:49:28 $
#
#    as.im()
#

as.im <- function(X, ...) {
  UseMethod("as.im")
}

as.im.im <- function(X, W=NULL, ...,
                     eps=NULL, dimyx=NULL, xy=NULL,
                     na.replace=NULL) {
  if(is.null(W)) {
    if(is.null(eps) && is.null(dimyx) && is.null(xy))
      return(na.handle.im(X, na.replace))
    # pixel raster determined by dimyx etc
    W <- as.mask(as.rectangle(X), eps=eps, dimyx=dimyx, xy=xy)
    # invoke as.im.owin
    Y <- as.im(W)
  } else {
    # apply dimyx (etc) if present,
    # otherwise use W to determine pixel raster
    Y <- as.im(W, eps=eps, dimyx=dimyx, xy=xy)
  }
  # resample X onto raster of Y
  phase <- c((Y$xcol[1] - X$xcol[1])/X$xstep,
             (Y$yrow[1] - X$yrow[1])/X$ystep)
  Y$v <- matrixsample(X$v, Y$dim, phase=round(phase))

  # inherit pixel data type from X
  Y$type <- X$type
  if(Y$type == "factor")
    levels(Y) <- levels(X)

  return(na.handle.im(Y, na.replace))
}

as.im.owin <- function(X, W=NULL, ...,
                       eps=NULL, dimyx=NULL, xy=NULL,
                       na.replace=NULL, value=1) {
  if(!(is.null(eps) && is.null(dimyx) && is.null(xy))) {
    # raster dimensions determined by dimyx etc
    # convert X to a mask 
    M <- as.mask(X, eps=eps, dimyx=dimyx, xy=xy)
    # convert mask to image
    d <- M$dim
    v <- matrix(value, d[1], d[2])
    m <- M$m
    v[!m] <- if(is.null(na.replace)) NA else na.replace
    out <- im(v, M$xcol, M$yrow, unitname=unitname(X))
    return(out)
  }
  if(!is.null(W) && is.owin(W) && W$type == "mask") {
    # raster dimensions determined by W
    # convert W to zero image
    d <- W$dim
    Z <- im(matrix(0, d[1], d[2]), W$xcol, W$yrow, unitname=unitname(X))    
    # adjust values to indicator of X
    Z[X] <- 1
    if(missing(value) && is.null(na.replace)) {
      # done
      out <- Z
    } else {
      # map {0, 1} to {na.replace, value}
      v <- matrix(ifelse(Z$v == 0, na.replace, value), d[1], d[2])
      out <- im(v, W$xcol, W$yrow, unitname=unitname(X))
    }
    return(out)
  }
  if(X$type == "mask") {
    # raster dimensions determined by X
    # convert X to image
    d <- X$dim
    v <- matrix(value, d[1], d[2])
    m <- X$m
    v[!m] <- if(is.null(na.replace)) NA else na.replace
    out <- im(v, X$xcol, X$yrow, unitname=unitname(X))
    return(out)
  }
  # X is not a mask.
  # W is either missing, or is not a mask.
  # Convert X to a image using default settings
  M <- as.mask(X)
  # convert mask to image
  d <- M$dim
  v <- matrix(value, d[1], d[2])
  m <- M$m
  v[!m] <- if(is.null(na.replace)) NA else na.replace
  out <- im(v, M$xcol, M$yrow, unitname=unitname(X))
  return(out)
}

as.im.function <- function(X, W=NULL, ...,
                           eps=NULL, dimyx=NULL, xy=NULL,
                           na.replace=NULL) {
  f <- X
  if(is.null(W))
    stop("A window W is required")
  W <- as.owin(W)
  W <- as.mask(W, eps=eps, dimyx=dimyx, xy=xy)
  m <- W$m
  funnywindow <- !all(m)

  xx <- as.vector(raster.x(W))
  yy <- as.vector(raster.y(W))
  lev <- NULL

  # evaluate function value at each pixel 
  if(!funnywindow) 
    values <- f(xx, yy, ...)
  else {
    # evaluate only inside window
    inside <- as.vector(m)
    val <- f(xx[inside], yy[inside], ...)
    # create space for full matrix
    msize <- length(m)
    values <-
      if(!is.factor(val))
        vector(mode=typeof(val), length=msize)
      else {
        lev <- levels(val)
        factor(rep(lev[1], msize), levels=lev)
      }
    # copy values, assigning NA outside window
    values[inside] <- val
    values[!inside] <- NA
  }
  
  if(is.factor(values)) 
    lev <- levels(values)
  
  out <- im(values, W$xcol, W$yrow, lev, unitname=unitname(W))
  return(na.handle.im(out, na.replace))
}

as.im.default <- function(X, W=NULL, ...,
                          eps=NULL, dimyx=NULL, xy=NULL,
                          na.replace=NULL) {

  if((is.vector(X) || is.factor(X)) && length(X) == 1) {
    # numerical value: interpret as constant function
    xvalue <- X
    X <- function(xx, yy, ...) { rep(xvalue, length(xx)) }
    return(as.im(X, W, ..., dimyx=dimyx, na.replace=na.replace))
  }
  
  if(is.list(X) && checkfields(X, c("x","y","z"))) {
    stopifnot(is.matrix(X$z))
    z <- X$z
    y <- X$y
    x <- X$x
    # Usual S convention as in contour.default() and image.default()
    # Rows of z correspond to x values.
    nr <- nrow(z)
    nc <- ncol(z)
    lx <- length(x)
    ly <- length(y)
    if(lx == nr + 1)
      x <- (x[-1] + x[-lx])/2
    else if(lx != nr)
      stop("length of x coordinate vector does not match number of rows of z")
    if(ly == nc + 1)
      y <- (y[-1] + y[-ly])/2
    else if(ly != nc)
      stop("length of y coordinate vector does not match number of columns of z")
    # convert to class "im"
    out <- im(t(z), x, y)
    # now apply W and dimyx if present
    if(is.null(W) && !(is.null(eps) && is.null(dimyx) && is.null(xy)))
      out <- as.im(out, eps=eps, dimyx=dimyx, xy=xy)
    else if(!is.null(W))
      out <- as.im(out, W=W, eps=eps, dimyx=dimyx, xy=xy)
    return(na.handle.im(out, na.replace))
  }
  stop("Can't convert X to a pixel image")
}

as.im.ppp <- function(X, ...) {
  pixellate(X, ..., weights=NULL, zeropad=FALSE)
}

na.handle.im <- function(X, na.replace) {
if(is.null(na.replace))
  return(X)
if(length(na.replace) != 1)
  stop("na.replace should be a single value")
X$v[is.na(X$v)] <- na.replace
return(X)
}