Add Element2d.SetGeomInfo() Python API for external mesh curving

[ksugahar]

Summary

Add a SetGeomInfo method to Element2d that allows setting the UV parametric coordinates (geominfo) for surface element vertices.

Motivation

This is essential for high-order curving of externally imported meshes (e.g., from Gmsh, Cubit, or other mesh generators). When meshes are imported without geometry, the geominfo is not set automatically, which prevents mesh.Curve(order) from working correctly.

Usage

from netgen.meshing import *

# After importing mesh and setting up geometry
for el in mesh.Elements2D():
    for i in range(len(el.vertices)):
        # Get UV coordinates from geometry for this vertex
        u, v = compute_uv_for_vertex(el.vertices[i])
        el.SetGeomInfo(i, u, v)

# Now curving works correctly
mesh.Curve(order)

API

Element2d.SetGeomInfo(vertex_index, u, v, trignum=0)

Parameters:

• vertex_index: 0-based index of the vertex within the element
• u, v: Surface parametric coordinates
• trignum: Triangle number for STL meshing (default: 0)

Related

• Feature request: https://forum.ngsolve.org/t/feature-request-python-api-for-high-order-curving-of-externally-imported-meshes/3810
• Complements existing Element2d.IsValid(), Element2d.IsDeleted(), and Element2d.geominfo (read-only) methods

🤖 Generated with Claude Code

[ksugahar]

Successful Workflow Report: 3D High-Order Elements with SetGeomInfo API

I've been using this PR to enable high-order curving for externally imported meshes from Coreform Cubit. The results are excellent!

Workflow

1. OCC: Create geometry and name faces (name_occ_faces())
2. OCC: Export to STEP (face names preserved)
3. Cubit: Import STEP, generate mesh
4. Export: Use name-based face mapping to Netgen mesh
5. SetGeomInfo: Compute UV parameters analytically and call el.SetGeomInfo(i, u, v)
6. mesh.Curve(order): High-order curving now works correctly!

Accuracy Results

Geometry	Curve(2) Error	Curve(3) Error
Complex (Boolean ops)	0.0021%	0.0004%
Cylinder	0.0027%	0.0006%
Sphere	0.0027%	0.0004%
Torus	0.0010%	0.0003%

This achieves Netgen-native accuracy for externally imported meshes!

Published Library

The workflow is implemented in my Python library:

• PyPI: coreform-cubit-mesh-export 1.12.0
• GitHub: ksugahar/Coreform_Cubit_Mesh_Export

Key Functions

# Set UV for analytic surfaces
set_cylinder_geominfo(ngmesh, radius, height, center, axis)
set_sphere_geominfo(ngmesh, radius, center)
set_torus_geominfo(ngmesh, major_radius, minor_radius, center, axis)
set_cone_geominfo(ngmesh, base_radius, height, center, axis)

Why This Matters

• Cubit users can now use NGSolve's high-order elements with correct curving
• Hex meshes from Cubit work correctly with mesh.Curve()
• Complex geometries (Boolean operations) achieve the same accuracy as Netgen-native meshing

Thank you for implementing this API! It's exactly what was needed for external mesh curving.

[ksugahar]

Binary Release Available

I've published a pre-built Windows binary with this PR applied:

Download: NGSolve 6.2.2601 + SetGeomInfo API

This allows users to test the SetGeomInfo API without building from source.

Installation

1. Download and extract ngsolve-6.2.2601-setgeominfo-win64.zip
2. Add to Python path:

import sys
sys.path.insert(0, "path/to/extracted/Lib/site-packages")
import ngsolve

The binary includes the Periodic BC fix (upstream commit 2581a74) and PR #232.