Create Edge/Face Sets from Outward Normals

For some meshes, side sets can be generated based on outward normals, especially when the boundary sides have well-defined directions.

While side sets technically only need numeric IDs, it is strongly recommended to also assign descriptive names for easier reference. The example below shows how to do this in code.

Before calling Mesh::boundary_edges, make sure to first call Mesh::set_up. This step is essential—it initializes the edge IDs that will later be used to form side sets.

The general approach is straightforward:

1. Loop over all boundary edges.

2. Compute the outward normal for each edge.

3. Group edges with similar normals into “buckets.” Each bucket represents a potential side set.

Once the buckets are created, you can register each one as a side set by calling:

Mesh.set_edge_set(id, edges)

Here, id must be a positive integer.

To give the edge set a meaningful name, use:

Mesh.set_edge_set_name(id, name)

This links the numeric ID to a user-friendly label, making your mesh definition easier to read and maintain.

Note

This capability is also supported in three dimensions. Use Mesh.boundary_faces instead of Mesh.boundary_edges, and ensure that outward normals have three components instead of two. Then, use set_face_set and set_face_set_name to set the face set and its name.

Example:

import krado
import math

# create a mesh, for example via:
#   mesh = krado.import_mesh("mesh.exo")

# This must be called so we can use `boundary_edges` and `outward_normal`
mesh.set_up()

face_sets = {
   "left": [],
   "right": [],
   "bottom": [],
   "other": []
}
bnd_edges = mesh.boundary_edges()
for edge in bnd_edges:
    n = mesh.outward_normal(edge)
    if n.is_equal(krado.Vector(1, 0)):
        face_sets["right"].append(edge)
    elif n.is_equal(krado.Vector(-1, 0)):
        face_sets["left"].append(edge)
    elif n.is_equal(krado.Vector(0, -1)):
        face_sets["bottom"].append(edge)
    else:
        face_sets["other"].append(edge)

for (idx, name) in enumerate(face_sets):
    # pick some ID
    id = 1000 + idx
    mesh.set_edge_set(id, face_sets[name])
    mesh.set_edge_set_name(id, name)

# export mesh here