An object of class "ashape3d" that represents the
\(\alpha\)-shape of a given sample of points in the three-dimensional
space, see ashape3d.
indexAlpha
A single value or vector with the indexes of
as3d$alpha that should be used for the computation, see Details.
display
Logical, if TRUE, surfaceNormals open a new rgl device
and display the related \(\alpha\)-shape and its normals vectors.
col
Color of the normal vectors.
scale
Scale parameter to control the length of the surface normals,
only affect display.
…
Material properties. See rgl.material for
details.
Value
If indexAlpha is a single value then the function returns an
object of class "normals" with the following components:
normals
Three-column matrix with the euclidean coordinates of the
normal vectors.
centers
Three-column matrix with the euclidean
coordinates of the centers of the triangles that form the
\(\alpha\)-shape.
Otherwise surfaceNormals returns a list of class
"normals-List" (each object in the list as described above).
Details
The function surfaceNormals computes the normal vectors of all the
triangles which belong to the boundary of the \(\alpha\)-shape for each
value of \(\alpha\) in x$alpha[indexAlpha]. The magnitude of each
vector is equal to the area of its associated triangle.
If indexAlpha="all" or indexAlpha="ALL" then the function
computes the normal vectors for all values of \(\alpha\) in
as3d$alpha.