Spatial morphers form spatial add-ons to the set of morphers provided by tidygraph. These functions are not meant to be called directly. They should either be passed into morph to create a temporary alternative representation of the input network. Such an alternative representation is a list of one or more network objects. Single elements of that list can be extracted directly as a new network by passing the morpher to convert instead, to make the changes lasting rather than temporary. Alternatively, if the morphed state contains multiple elements, all of them can be extracted together inside a tbl_df by passing the morpher to crystallise.

to_spatial_contracted(
x,
...,
simplify = FALSE,
summarise_attributes = "ignore",
store_original_data = FALSE
)

to_spatial_directed(x)

to_spatial_explicit(x, ...)

to_spatial_neighborhood(x, node, threshold, weights = NULL, from = TRUE, ...)

to_spatial_shortest_paths(x, ...)

to_spatial_simple(
x,
remove_multiple = TRUE,
remove_loops = TRUE,
summarise_attributes = "first",
store_original_data = FALSE
)

to_spatial_smooth(x, store_original_data = FALSE)

to_spatial_subdivision(x)

to_spatial_subset(x, ..., subset_by = NULL)

to_spatial_transformed(x, ...)

## Arguments

x An object of class sfnetwork. Arguments to be passed on to other functions. See the description of each morpher for details. Should the network be simplified after contraction? This means that multiple edges and loop edges will be removed. Multiple edges are introduced by contraction when there are several connections between the same groups of nodes. Loop edges are introduced by contraction when there are connections within a group. Note however that setting this to TRUE also removes multiple edges and loop edges that already existed before contraction. Defaults to FALSE. Whenever multiple features (i.e. nodes and/or edges) are merged into a single feature during morphing, how should their attributes be combined? Several options are possible, see igraph-attribute-combination for details. Whenever multiple features (i.e. nodes and/or edges) are merged into a single feature during morphing, should the data of the original features be stored as an attribute of the new feature, in a column named .orig_data. This is in line with the design principles of tidygraph. Defaults to FALSE. The geospatial point for which the neighborhood will be calculated. Can be an integer, referring to the index of the node for which the neighborhood will be calculated. Can also be an object of class sf or sfc, containing a single feature. In that case, this point will be snapped to its nearest node before calculating the neighborhood. When multiple indices or features are given, only the first one is taken. The threshold distance to be used. Only nodes within the threshold distance from the reference node will be included in the neighborhood. Should be a numeric value in the same units as the weight values used for distance calculation. The edge weights used to calculate distances on the network. Can be a numeric vector giving edge weights, or a column name referring to an attribute column in the edges table containing those weights. If set to NULL, the values of a column named weight in the edges table will be used automatically, as long as this column is present. If not, the geographic edge lengths will be calculated internally and used as weights. Should distances be calculated from the reference node towards the other nodes? Defaults to TRUE. If set to FALSE, distances will be calculated from the other nodes towards the reference node instead. Should multiple edges be merged into one. Defaults to TRUE. Should loop edges be removed. Defaults to TRUE. Whether to create subgraphs based on nodes or edges.

## Value

Either a morphed_sfnetwork, which is a list of one or more sfnetwork objects, or a morphed_tbl_graph, which is a list of one or more tbl_graph objects. See the description of each morpher for details.

## Details

It also possible to create your own morphers. See the documentation of morph for the requirements for custom morphers.

## Functions

• to_spatial_contracted: Combine groups of nodes into a single node per group. ... is forwarded to group_by to create the groups. The centroid of the group of nodes will be used as geometry of the contracted node. If edge are spatially explicit, edge geometries are updated accordingly such that the valid spatial network structure is preserved. Returns a morphed_sfnetwork containing a single element of class sfnetwork.

• to_spatial_directed: Make a network directed in the direction given by the linestring geometries of the edges. Differs from to_directed, which makes a network directed based on the node indices given in the from and to columns. In undirected networks these indices may not correspond with the endpoints of the linestring geometries. Returns a morphed_sfnetwork containing a single element of class sfnetwork. This morpher requires edges to be spatially explicit. If not, use to_directed.

• to_spatial_explicit: Create linestring geometries between source and target nodes of edges. If the edges data can be directly converted to an object of class sf using st_as_sf, extra arguments can be provided as ... and will be forwarded to st_as_sf internally. Otherwise, straight lines will be drawn between the source and target node of each edge. Returns a morphed_sfnetwork containing a single element of class sfnetwork.

• to_spatial_neighborhood: Limit a network to the spatial neighborhood of a specific node. ... is forwarded to node_distance_from (if from is TRUE) or node_distance_to (if from is FALSE). Returns a morphed_sfnetwork containing a single element of class sfnetwork.

• to_spatial_shortest_paths: Limit a network to those nodes and edges that are part of the shortest path between two nodes. ... is evaluated in the same manner as st_network_paths with type = 'shortest'. Returns a morphed_sfnetwork that may contain multiple elements of class sfnetwork, depending on the number of requested paths. When unmorphing only the first instance of both the node and edge data will be used, as the the same node and/or edge can be present in multiple paths.

• to_spatial_simple: Remove loop edges and/or merges multiple edges into a single edge. Multiple edges are edges that have the same source and target nodes (in directed networks) or edges that are incident to the same nodes (in undirected networks). When merging them into a single edge, the geometry of the first edge is preserved. The order of the edges can be influenced by calling arrange before simplifying. Returns a morphed_sfnetwork containing a single element of class sfnetwork.

• to_spatial_smooth: Construct a smoothed version of the network by iteratively removing pseudo nodes, while preserving the connectivity of the network. In the case of directed networks, pseudo nodes are those nodes that have only one incoming and one outgoing edge. In undirected networks, pseudo nodes are those nodes that have two incident edges. Connectivity of the network is preserved by concatenating the incident edges of each removed pseudo node. Returns a morphed_sfnetwork containing a single element of class sfnetwork.

• to_spatial_subdivision: Construct a subdivision of the network by subdividing edges at each interior point that is equal to any other interior or boundary point in the edges table. Interior points in this sense are those points that are included in their linestring geometry feature but are not endpoints of it, while boundary points are the endpoints of the linestrings. The network is reconstructed after subdivision such that edges are connected at the points of subdivision. Returns a morphed_sfnetwork containing a single element of class sfnetwork. This morpher requires edges to be spatially explicit.

• to_spatial_subset: Subset the network by applying a spatial filter, i.e. a filter on the geometry column based on a spatial predicate. ... is evaluated in the same manner as st_filter. Returns a morphed_sfnetwork containing a single element of class sfnetwork. For filters on an attribute column, use to_subgraph.

• to_spatial_transformed: Transform the geospatial coordinates of the network into a different coordinate reference system. ... is evaluated in the same manner as st_transform. Returns a morphed_sfnetwork containing a single element of class sfnetwork.

The vignette on spatial morphers.

## Examples

library(sf, quietly = TRUE)
library(tidygraph, quietly = TRUE)

net = as_sfnetwork(roxel, directed = FALSE) %>%
st_transform(3035)

# Temporary changes with morph and unmorph.
net %>%
activate("edges") %>%
mutate(weight = edge_length()) %>%
morph(to_spatial_shortest_paths, from = 1, to = 10) %>%
mutate(in_paths = TRUE) %>%
unmorph()
#> # A sfnetwork with 701 nodes and 851 edges
#> #
#> # CRS:  EPSG:3035
#> #
#> # An undirected multigraph with 14 components with spatially explicit edges
#> #
#> # Edge Data:     851 × 7 (active)
#> # Geometry type: LINESTRING
#> # Dimension:     XY
#> # Bounding box:  xmin: 4150707 ymin: 3206375 xmax: 4152367 ymax: 3208565
#>    from    to name     type                             geometry weight in_paths
#>   <int> <int> <chr>    <fct>                    <LINESTRING [m]>    [m] <lgl>
#> 1     1     2 Havixbe… resid… (4151491 3207923, 4151474 3207946)   28.9 NA
#> 2     3     4 Pieners… secon… (4151398 3207777, 4151390 3207727…  108.  NA
#> 3     5     6 Schulte… resid… (4151408 3207539, 4151417 3207573…   54.4 NA
#> 4     7     8 NA       path   (4151885 3206698, 4151861 3206711…  155.  NA
#> 5     9    10 Welsing… resid… (4151732 3207017, 4151721 3206809)  209.  TRUE
#> 6    11    12 NA       footw… (4152152 3206984, 4152143 3206932…   63.0 NA
#> # … with 845 more rows
#> #
#> # Node Data:     701 × 1
#> # Geometry type: POINT
#> # Dimension:     XY
#> # Bounding box:  xmin: 4150707 ymin: 3206375 xmax: 4152367 ymax: 3208565
#>            geometry
#>         <POINT [m]>
#> 1 (4151491 3207923)
#> 2 (4151474 3207946)
#> 3 (4151398 3207777)
#> # … with 698 more rows

# Lasting changes with convert.
net %>%
activate("edges") %>%
mutate(weight = edge_length()) %>%
convert(to_spatial_shortest_paths, from = 1, to = 10)
#> # A sfnetwork with 18 nodes and 17 edges
#> #
#> # CRS:  EPSG:3035
#> #
#> # An unrooted tree with spatially explicit edges
#> #
#> # Edge Data:     17 × 7 (active)
#> # Geometry type: LINESTRING
#> # Dimension:     XY
#> # Bounding box:  xmin: 4151491 ymin: 3206809 xmax: 4151802 ymax: 3207923
#>    from    to name   type                       geometry weight .tidygraph_edge…
#>   <int> <int> <chr>  <fct>              <LINESTRING [m]>    [m]            <int>
#> 1     2     3 Welsi… resid… (4151732 3207017, 4151721 3…  209.                 5
#> 2     2     6 Nottu… resid… (4151732 3207017, 4151755 3…   84.4               94
#> 3     5     8 Roxel… secon… (4151531 3207830, 4151535 3…   98.3              159
#> 4     8    12 Roxel… secon… (4151519 3207865, 4151524 3…   37.0              295
#> 5     5     7 Dorff… resid… (4151620 3207798, 4151621 3…   49.3              486
#> 6     9    15 Dorff… resid… (4151786 3207133, 4151794 3…   32.7              591
#> # … with 11 more rows
#> #
#> # Node Data:     18 × 2
#> # Geometry type: POINT
#> # Dimension:     XY
#> # Bounding box:  xmin: 4151491 ymin: 3206809 xmax: 4151802 ymax: 3207923
#>            geometry .tidygraph_node_index
#>         <POINT [m]>                 <int>
#> 1 (4151491 3207923)                     1
#> 2 (4151732 3207017)                     9
#> 3 (4151721 3206809)                    10
#> # … with 15 more rows