R/smoothGeom.r

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

#' Smooth the geometry of a vector
#'
#' @description `smoothGeom()` makes line segments of a vector appear less angular.
#'
#' @param x A `GVector`.
#'
#' @param method Character: Method used to smooth line segments. Partial matching is used, and case does not matter:
#'
#' * `"Hermite"`: Hermite interpolation (default): Guarantees that the output vector always passes through the original points. This method adds points (possibly many) by constructing cubic splines with points approximately `dist` apart. The number of points can be reduced by specifying a smaller value of `angle`, which specifies the minimum angle between two successive line segments.
#' * `"Chaiken"`: Chaiken's algorithm: Guarantees that the new vector always touches the midpoint of each original line segment. The points on the new line are at least `dist` apart.
#'
#' @param dist Numeric > 0 of `NULL` (default): Minimum distance (see `method`). Units are in map units. If `NULL`, then 2% of the minimum of the x-, y-, and z-extent will be used.
#'
#' @param angle Numeric > 0: Maximum angle for the Hermite algorithm. Default is 3.
#'
#' @seealso [simplifyGeom()], [terra::simplifyGeom()], [geometry cleaning][breakPolys], **GRASS** manual page for module `v.generalize` (see `grassHelp("v.generalize")`)
#'
#' @returns A `GVector`.
#'
#' @example man/examples/ex_simplify_smooth_clean_GVector.r
#'
#' @aliases smoothGeom
#' @rdname smoothGeom
#' @exportMethod smoothGeom
methods::setMethod(
	f = "smoothGeom",
	signature = c(x = "GVector"),
	function(x, method = "Hermite", dist = NULL, angle = 3) {

	# automatic distance
	if (is.null(dist)) {
		extent <- ext(x, vector=TRUE)
		xext <- extent[2L] - extent[1L]
		yext <- extent[4L] - extent[3L]
		zext <- diff(zext)
		dist <- 0.02 * min(xext, yext, zext, na.rm=TRUE)
	} else {
		if (dist < 0) stop("Argument `dist` must be > 0.")
	}

	.locationRestore(x)
	
	method <- tolower(method)
	method <- omnibus::pmatchSafe(method, c("hermite", "chaiken"))
	
	if (method == "hermite" && angle < 0) stop("Argument `angle` must be >0.")
	
	src <- .makeSourceName("generalized", "vect")
	args <- list(
		cmd = "v.generalize",
		input = sources(x),
		output = src,
		method = method,
		threshold = dist,
		flags = c(.quiet(), "overwrite"),
		intern = TRUE
	)

	if (method == "hermite") args$angle_thresh <- angle
	
	do.call(rgrass::execGRASS, args=args)
	.makeGVector(src)

	} # EOF
)