Add as sfnetwork methods

DESCRIPTION

@@ -38,11 +38,12 @@ Imports:
   tidygraph,
   utils
 Suggests:
-  dplyr,
-  fansi,
-  ggplot2,
-  knitr,
-  testthat
+    dplyr,
+    fansi,
+    ggplot2,
+    knitr,
+    testthat,
+    spatstat
 RoxygenNote: 7.1.0
 VignetteBuilder: knitr
 URL: https://luukvdmeer.github.io/sfnetworks/, https://github.com/luukvdmeer/sfnetworks

NAMESPACE

@@ -3,6 +3,8 @@
 S3method("st_crs<-",sfnetwork)
 S3method("st_geometry<-",sfnetwork)
 S3method(as_sfnetwork,default)
+S3method(as_sfnetwork,linnet)
+S3method(as_sfnetwork,psp)
 S3method(as_sfnetwork,sf)
 S3method(as_sfnetwork,sfNetwork)
 S3method(as_sfnetwork,sfnetwork)

R/sfnetwork.R

@@ -3,7 +3,7 @@
 #' \code{sfnetwork} is a tidy data structure for geospatial networks. It extends
 #' the graph manipulation functionalities of the
 #' \code{\link[tidygraph]{tidygraph-package}} package into the domain of
-#' geospatial networks, where the nodes and optionally also the edges are 
+#' geospatial networks, where the nodes and optionally also the edges are
 #' embedded in geographical space, and enables to apply the spatial analytical
 #' function from the \code{\link[sf:sf]{sf-package}} directly to the network.
 #'
@@ -35,7 +35,7 @@
 #' constructing the network. These checks guarantee a valid spatial network
 #' structure. For the nodes, this means that they all should have \code{POINT}
 #' geometries. In the case of spatially explicit edges, it is also checked that
-#' all edges have \code{LINESTRING} geometries, nodes and edges have the same 
+#' all edges have \code{LINESTRING} geometries, nodes and edges have the same
 #' CRS and boundary points of edges match their corresponding node coordinates.
 #' These checks are important, but also time consuming. If you are already sure
 #' your input data meet the requirements, the checks are unneccesary and can be
@@ -48,7 +48,7 @@
 #'
 #' @importFrom tidygraph tbl_graph
 #' @export
-sfnetwork = function(nodes, edges, directed = TRUE, edges_as_lines = NULL, 
+sfnetwork = function(nodes, edges, directed = TRUE, edges_as_lines = NULL,
                      force = FALSE, ...) {
   # Automatically set edges_as_lines if not given.
   if (is.null(edges_as_lines)) {
@@ -129,7 +129,7 @@ nodes_to_sf = function(nodes, ...) {
 #'
 #' @param x object to be converted into an \code{\link{sfnetwork}} object.
 #'
-#' @param ... arguments passed on to the \code{\link{sfnetwork}} construction 
+#' @param ... arguments passed on to the \code{\link{sfnetwork}} construction
 #' function.
 #'
 #' @return An object of class \code{\link{sfnetwork}}.
@@ -200,6 +200,55 @@ as_sfnetwork.tbl_graph = function(x, ...) {
   do.call("sfnetwork", args)
 }
 
+#' @name as_sfnetwork
+#' @importFrom sf st_as_sf st_collection_extract
+#' @export
+#' @examples
+#' # Examples for psp method
+#' if (require(spatstat)) {
+#' set.seed(42)
+#' test_psp = psp(runif(10), runif(10), runif(10), runif(10), window=owin())
+#' plot(test_psp, main = "spatstat input")
+#' test_psp_as_sfnetwork = as_sfnetwork(test_psp)
+#' plot(test_psp_as_sfnetwork, main = "sfnetworks output")
+#' }
+#'
+as_sfnetwork.psp = function(x, ...) {
+  # I think that the easiest method for transforming a Line Segment Pattern
+  # (psp) object into sfnetwork format is to transform it into sf format and
+  # then apply the usual methods.
+  x_sf = sf::st_as_sf(x)
+
+  # x_sf is an sf object composed by 1 POLYGON (the window of the psp object)
+  # and several LINESTRINGs (the line segments). I'm not sure if and how we can
+  # use the window object so I will extract only the LINESTRINGs.
+  x_linestring = sf::st_collection_extract(x_sf, "LINESTRING")
+
+  # apply as_sfnetwork.sf
+  as_sfnetwork(x_linestring, ...)
+}
+
+#' @name as_sfnetwork
+#' @export
+#' @examples
+#' # Examples for linnet method
+#' if (require(spatstat)) {
+#' plot(simplenet, main = "spatstat input")
+#' simplenet_as_sfnetwork = as_sfnetwork(simplenet)
+#' plot(simplenet_as_sfnetwork, main = "sfnetworks output")
+#' }
+#'
+as_sfnetwork.linnet = function(x, ...) {
+  # IMO the easiest approach is the same as for psp objects, i.e. converting the
+  # linnet object into a psp format and then applying the corresponding method.
+  if (!requireNamespace("spatstat", quietly = TRUE)) {
+    stop("package spatstat required, please install it first")
+  }
+
+  x_psp = spatstat::as.psp(x)
+  as_sfnetwork(x_psp, ...)
+}
+
 #' @importFrom sf st_as_sf st_crs st_geometry
 #' @importFrom rlang !!
 #' @importFrom tibble trunc_mat