Compute border of a label.

Compute the border of a label (i.e., a subset of the vertices of a mesh). The border thickness can be specified. Useful to draw the outline of a region, e.g., a significant cluster on the surface or a part of a ROI from a brain parcellation.

Usage

label.border(
  surface_mesh,
  label,
  inner_only = TRUE,
  expand_inwards = 0L,
  derive = FALSE
)

Arguments

surface_mesh

surface mesh, as loaded by subject.surface or read.fs.surface.

label

instance of class fs.label or an integer vector, the vertex indices. This function only makes sense if they form a patch on the surface, but that is not checked.

inner_only

logical, whether only faces consisting only of label_vertices should be considered to be label faces. If FALSE, faces containing at least one label vertex will be used. Defaults to TRUE. Leave this alone if in doubt, especially if you want to draw several label borders which are directly adjacent on the surface.

expand_inwards

integer, border thickness extension. If given, once the border has been computed, it is extended by the given graph distance. It is guaranteed that the border only extends inwards, i.e., it will never extend to vertices which are not part of the label.

derive

logical, whether the returned result should also include the border edges and faces in addition to the border vertices. Takes longer if requested, defaults to FALSE.

Value

the border as a list with the following entries: vertices: integer vector, the vertex indices of the border. Iff the parameter derive is TRUE, the following two additional fields are included: edges: integer matrix of size (n, 2) for n edges. Each row defines an edge by its start and target vertex. faces: integer vector, the face indices of the border.

See also

Other surface mesh functions: face.edges(), mesh.vertex.included.faces(), mesh.vertex.neighbors(), subject.surface(), vis.path.along.verts()