#' Skew geometric objects
#'
#' Skew geometric objects by a shear factor in x and y dimension.
#' @param obj [gridded(1)][geom]\cr the object to skew.
#' @param x [numeric(1)][numeric]\cr the shear factor in x dimension.
#' @param y [numeric(1)][numeric]\cr the shear factor in y dimension.
#' @param fid [integerish(.)][integer]\cr in case only a subset of features shall
#' be skewed, specify that here.
#' @param update [logical(1)][logical]\cr whether or not to update the window slot
#' after skewing.
#' @return \code{geom} of the skewed \code{obj}.
#' @family geometry tools
#' @examples
#' # skew several features
#' geo_vis(gtGeoms$polygon, linewidth = 3)
#' newPoly <- geo_skew(obj = gtGeoms$polygon, x = 0.5, update = FALSE)
#' geo_vis(geom = newPoly, linecol = "green", new = FALSE)
#'
#' # skew a single feature
#' geo_vis(gtGeoms$polygon, linewidth = 3)
#' newPoly <- geo_skew(obj = gtGeoms$polygon, x = 0.5, y = .7, fid = 2,
#' update = FALSE)
#' geo_vis(newPoly, linecol = "green", new = FALSE)
#' @importFrom checkmate assertNumeric assertLogical
#' @importFrom geomio getFeatures getGroups getPoints getWindow getNames getType
#' getProvenance
#' @importFrom dplyr bind_rows
#' @importFrom tibble tibble
#' @importFrom methods new
#' @export
geo_skew <- function(obj, x = NULL, y = NULL, fid = NULL, update = TRUE){
assertNumeric(x = x, any.missing = FALSE, min.len = 1, null.ok = TRUE)
assertNumeric(x = y, any.missing = FALSE, min.len = 1, null.ok = TRUE)
assertNumeric(x = fid, lower = 1, finite = TRUE, any.missing = FALSE, null.ok = TRUE)
assertLogical(x = update, len = 1, any.missing = FALSE)
thePoints <- getPoints(x = obj)
# set default values
if(is.null(x)){
x <- 0
}
if(is.null(y)){
y <- 0
}
ids <- unique(thePoints$fid)
# identify fids to modify
existsID <- !is.null(fid)
if(existsID){
doSkew <- ids %in% fid
} else{
doSkew <- rep(TRUE, length(ids))
}
# repeat values to match fids
if(length(x) != length(ids)){
x <- rep(x, length.out = length(ids))
}
if(length(y) != length(ids)){
y <- rep(y, length.out = length(ids))
}
# modify vertices
temp <- NULL
for(i in seq_along(ids)){
tempCoords <- thePoints[thePoints$fid == ids[i],]
newCoords <- tempCoords
if(doSkew[i]){
centCoords <- tempCoords[!duplicated(tempCoords),]
centroid <- tibble(x = mean(x = centCoords$x), y = mean(x = centCoords$y))
newCoords$x <- tempCoords$x + x[[i]] * tempCoords$y
newCoords$y <- tempCoords$y + y[[i]] * tempCoords$x
centCoords <- newCoords[!duplicated(newCoords),]
newCentroid <- tibble(x = mean(x = centCoords$x), y = mean(x = centCoords$y))
offset <- newCentroid - centroid
newCoords$x <- newCoords$x - offset$x
newCoords$y <- newCoords$y - offset$y
}
temp <- bind_rows(temp, newCoords)
}
# update window
if(update){
window <- tibble(x = c(min(temp$x), max(temp$x)),
y = c(min(temp$y), max(temp$y)))
} else {
window <- getWindow(x = obj)
}
# make history
if(length(ids) == 1){
hist <- paste0("geom was skewed.")
} else {
hist <- paste0("geoms were skewed.")
}
# make new geom
tempData <- list(features = getFeatures(x = obj), groups = getGroups(x = obj))
theData <- stats::setNames(list(tempData), getNames(x = obj))
out <- new(Class = "geom",
type = getType(x = obj)[1],
geometry = temp,
data = theData,
window = window,
crs = getCRS(x = obj),
provenance = c(getProvenance(x = obj), list(hist)))
return(out)
}
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