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#' Fortify method for classes from the sp package.
#'
#' To figure out the correct variable name for region, inspect
#' \code{as.data.frame(model)}.
#'
#' @param model \code{SpatialPolygonsDataFrame} to convert into a dataframe.
#' @param data not used by this method
#' @param region name of variable used to split up regions
#' @param ... not used by this method
#' @name fortify.sp
#' @examples
#' if (require("maptools")) {
#' sids <- system.file("shapes/sids.shp", package="maptools")
#' nc1 <- readShapePoly(sids,
#' proj4string = CRS("+proj=longlat +datum=NAD27"))
#' nc1_df <- fortify(nc1)
#' }
NULL
#' @rdname fortify.sp
#' @export
#' @method fortify SpatialPolygonsDataFrame
fortify.SpatialPolygonsDataFrame <- function(model, data, region = NULL, ...) {
attr <- as.data.frame(model)
# If not specified, split into regions based on polygons
if (is.null(region)) {
coords <- ldply(model@polygons,fortify)
message("Regions defined for each Polygons")
} else {
cp <- sp::polygons(model)
try_require("maptools")
# Union together all polygons that make up a region
unioned <- unionSpatialPolygons(cp, attr[, region])
coords <- fortify(unioned)
coords$order <- 1:nrow(coords)
}
coords
}
#' @rdname fortify.sp
#' @export
#' @method fortify SpatialPolygons
fortify.SpatialPolygons <- function(model, data, ...) {
ldply(model@polygons, fortify)
}
#' @rdname fortify.sp
#' @export
#' @method fortify Polygons
fortify.Polygons <- function(model, data, ...) {
subpolys <- model@Polygons
pieces <- ldply(seq_along(subpolys), function(i) {
df <- fortify(subpolys[[model@plotOrder[i]]])
df$piece <- i
df
})
within(pieces,{
order <- 1:nrow(pieces)
id <- model@ID
piece <- factor(piece)
group <- interaction(id, piece)
})
}
#' @rdname fortify.sp
#' @export
#' @method fortify Polygon
fortify.Polygon <- function(model, data, ...) {
df <- as.data.frame(model@coords)
names(df) <- c("long", "lat")
df$order <- 1:nrow(df)
df$hole <- model@hole
df
}
#' @rdname fortify.sp
#' @export
#' @method fortify SpatialLinesDataFrame
fortify.SpatialLinesDataFrame <- function(model, data, ...) {
ldply(model@lines, fortify)
}
#' @rdname fortify.sp
#' @export
#' @method fortify Lines
fortify.Lines <- function(model, data, ...) {
lines <- model@Lines
pieces <- ldply(seq_along(lines), function(i) {
df <- fortify(lines[[i]])
df$piece <- i
df
})
within(pieces,{
order <- 1:nrow(pieces)
id <- model@ID
piece <- factor(piece)
group <- interaction(id, piece)
})
}
#' @rdname fortify.sp
#' @export
#' @method fortify Line
fortify.Line <- function(model, data, ...) {
df <- as.data.frame(model@coords)
names(df) <- c("long", "lat")
df$order <- 1:nrow(df)
df
}
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