normalizeGraphSpace-methods: Normalize node coordinates to graph and image spaces

In RGraphSpace: A Lightweight Interface Between 'igraph' and 'ggplot2' Graphics

Normalize node coordinates to graph and image spaces

Description

Accessory functions to normalize node coordinates in GraphSpace, either by centering them within the graph boundaries or by mapping them to pixel coordinates of a background image.

Usage

## S4 method for signature 'GraphSpace'
normalizeGraphSpace(
  gs,
  mar = 0.1,
  use_image = FALSE,
  flip.x = FALSE,
  flip.y = FALSE,
  rotate.xy = FALSE,
  flip.v = FALSE,
  flip.h = FALSE,
  verbose = TRUE,
  image = deprecated()
)

## S4 method for signature 'GraphSpace'
cropGraphSpace(gs, crop.coord = c(0, 1, 0, 1), verbose = TRUE)

Arguments

gs	A GraphSpace object to be normalized.
mar	A single numeric value in [0, 0.5] controlling the size of the outer margins around the graph. Without an image, mar specifies symmetric margins as a fraction of the graph space. With an image, mar is interpreted as a fraction of the available image margins surrounding the graph.
use_image	Logical; if an image is available, whether to use it as a background reference map. When enabled, x and y graph coordinates are interpreted as pixel coordinates in the image matrix. Images can be inspected and assigned with gs_image.
flip.x	Logical; whether to flip the node coordinates along the x-axis.
flip.y	Logical; whether to flip the node coordinates along the y-axis. Useful for aligning nodes with image backgrounds, which often use an inverted coordinate system.
rotate.xy	Logical; whether to rotate x-y coordinates.
flip.v	Logical; whether to vertically flip the background image matrix (top-to-bottom) to align with the graph coordinate system.
flip.h	Logical; whether to horizontally flip the background image matrix (left-to-right) to align with the graph coordinate system.
verbose	A single logical value specifying to display detailed messages (when verbose=TRUE) or not (when verbose=FALSE).
image	Deprecated from RGraphSpace 1.3.0; use gs_image instead.
crop.coord	An optional numeric vector of length four specifying a cropping region (xmin, xmax, ymin, ymax), with values in normalized coordinates [0,1].

Details

These functions provide different strategies for coordinate transformation:

• normalizeGraphSpace: Re-scales node coordinates to a [0, 1] unit square based on the graph's bounding box (when use_image = FALSE) or maps them to pixel coordinates (when use_image = TRUE and an image is provided; see gs_image). It handles image-to-graph alignment via flip.\* and rotate.\* arguments, used to adjust the graph origin with the image matrix layout. Users should be aware of the potential discrepancy between image matrix orientation (top-down) and graph coordinates (bottom-up). The function attempts to automatically adjust the y-axis to align the graph's bottom-up coordinates with the image's top-down layout, but further manual adjustments might be required.

• cropGraphSpace: Subsets the normalized graph space into a specific region defined by crop.coord. It recalculates node positions and background image boundaries to maintain spatial consistency after cropping. This function requires a previously normalized GraphSpace object.

Value

A GraphSpace object with updated nodes and image slots.

Note

This is an accessory function typically called during the preprocessing of GraphSpace objects before rendering.

See Also

gs_image

Examples

library(RGraphSpace)
library(igraph)

# Create a star graph
gtoy1 <- make_full_graph(30)

# Create a GraphSpace
gs <- GraphSpace(gtoy1)

gs <- normalizeGraphSpace(gs)

gs_crop <- cropGraphSpace(gs, 
         crop.coord = c(0, 0.75, 0, 0.75))

RGraphSpace documentation built on June 13, 2026, 9:06 a.m.