find_all_neighbors: Find Node Neighbors in a Surface Mesh

In bbuchsbaum/neurosurf: Data structures and visualization for surface-based neuroimaging data

Find Node Neighbors in a Surface Mesh

Description

Identifies all neighboring nodes within a specified radius for a given surface mesh.

Usage

find_all_neighbors(
  surf,
  radius,
  edgeWeights,
  nodes = NULL,
  distance_type = c("euclidean", "geodesic", "spherical")
)

Arguments

surf	A SurfaceGeometry object or igraph object representing the mesh
radius	Numeric; the spatial radius within which to search for neighbors. Must be positive
edgeWeights	Numeric vector; weights for edges used in distance computation. Length must equal the number of edges
nodes	Integer vector; subset of nodes to find neighbors for. If NULL, uses all nodes
distance_type	Character; type of distance metric to use: "euclidean", "geodesic", or "spherical"

Details

The function supports three distance metrics: Euclidean, geodesic, and spherical. For spherical distances, the surface is assumed to be a sphere. The internal k-nearest-neighbor search is capped at vcount(g) - 1 to avoid requesting more neighbors than exist in the graph.

Value

A list of matrices, each containing neighbor information:

i	Source node index
j	Neighbor node index
d	Distance between nodes

Examples

# Load a sample inflated surface from the package
surf_file <- system.file("extdata", "std.8.lh.inflated.asc", package = "neurosurf")
surf <- readAsc(surf_file)

# Create edge weights (using uniform weights for simplicity)
g <- graph(surf)
edge_weights <- rep(1, length(E(g)))

# Find neighbors within a 10mm radius for the first 5 vertices
neighbors <- find_all_neighbors(surf, radius = 10, 
                               edgeWeights = edge_weights,
                               nodes = 1:5,
                               distance_type = "geodesic")

# Check the number of neighbors found for the first vertex
nrow(neighbors[[1]])

# Look at the first few neighbors of the first vertex
head(neighbors[[1]])

bbuchsbaum/neurosurf documentation built on June 10, 2025, 8:22 p.m.