Layout algorithm to visualize multilevel networks

layout_as_multilevel(
g,
type = "all",
FUN1,
FUN2,
params1 = NULL,
params2 = NULL,
ignore_iso = TRUE,
project2D = TRUE,
alpha = 35,
beta = 45
)

layout_igraph_multilevel(
g,
type = "all",
FUN1,
FUN2,
params1 = NULL,
params2 = NULL,
ignore_iso = TRUE,
alpha = 35,
beta = 45,
circular
)

## Arguments

g igraph object. Must have a vertex attribute "lvl" which is 1 or 2. one of "all", "separate","fix1" or "fix2". see details if type="separate", the layout function to be used for level 1 if type="separate", the layout function to be used for level 2 named list of parameters for FUN1 named list of parameters for FUN2 treatment of isolates within levels. see details logical. Defaults to TRUE (project to 2D). angle for isometric projection between 0 and 90 angle for isometric projection between 0 and 90 not used

## Value

matrix of xy coordinates

## Details

The algorithm internally computes a 3D layout where each level is in a separate y-plane. The layout is then projected into 2D via an isometric mapping, controlled by the parameters alpha and beta. It may take some adjusting to alpha and beta to find a good perspective.

If type="all", the layout is computed at once for the complete network. For type="separate", two user specified layout algorithms (FUN1 and FUN2) are used for the levels. The named lists param1 and param2 can be used to set parameters for FUN1 and FUN2. This option helpful for situations where different structural features of the levels should be emphasized.

For type="fix1" and type="fix2" only one of the level layouts is fixed. The other one is calculated by optimizing the inter level ties, such that they are drawn (almost) vertical.

The ignore_iso parameter controls the handling of isolates. If TRUE, nodes without inter level edges are ignored during the layout process and added at the end. If FALSE they are left unchanged

The layout_igraph_* function should not be used directly. It is only used as an argument for plotting with 'igraph'.

## Examples

library(igraph)
data("multilvl_ex")

# compute a layout for the whole network
xy <- layout_as_multilevel(multilvl_ex,type = "all", alpha = 25, beta = 45)

#compute a layout for each level separately and combine them
xy <- layout_as_multilevel(multilvl_ex,type = "separate",
FUN1 = layout_as_backbone,
FUN2 = layout_with_stress,
alpha = 25, beta = 45)