SG Manifest

Normative specification of the SG manifest (*.sg.json), the primary on-disk form of a structure gene in sgio.

No single file format fully describes an SG: an Abaqus .inp or Gmsh .msh carries no sgdim, model type or model space, a .msh carries no materials, and a SwiftComp input does not state its own smdim. A manifest holds these SG-level parameters and references exactly one model file that holds the rest.

import sgio

sg = sgio.read('section.sg.json', 'sg_manifest')
sgio.convert('section.sg.json', 'section.sg', 'sg_manifest', 'vabs')

# Writes section.msh and section.sg.json
sgio.write(
    sg, 'section.sg.json', 'sg_manifest',
    model_file='section.msh', model_file_format='gmsh',
)

Schema (version 1)

{
  "sg_manifest_version": 1,
  "model_file": {"path": "section.msh", "format": "gmsh"},
  "sgdim": 2,
  "model_type": "BM2",
  "model_space": "xy",
  "initial_twist": 0.0,
  "initial_curvature": [0.0, 0.0],
  "oblique": [1.0, 0.0],
  "config": {"analysis": 0, "physics": 0},
  "materials": [
    {"name": "carbon", "model": "sd1", "isotropy": 1, "elastic": {"e1": 1.4e11}}
  ],
  "sections": [
    {"name": "ply_0", "id": 1, "material": "carbon", "orientation": 0.0},
    {"name": "ply_45", "id": 2, "material": "carbon", "orientation": 45.0}
  ]
}

Field	Rule
sg_manifest_version	required; unknown versions are rejected
model_file.path	required; relative to the manifest directory
model_file.format	required; abaqus, gmsh, swiftcomp or vabs
model_file.format_version	required for swiftcomp and vabs; not allowed for other formats, whose version is read from the file
sgdim	required; never inferred from element dimension
model_type	required; the same string the API takes (SD1, PL1, BM2, …)
model_space	mesh axes of a 1D/2D SG (x/y/z, xy/yz/zx); required for sgdim 1 and 2 unless the model file format defines it; not allowed for sgdim 3
initial_twist, initial_curvature, oblique	optional beam/shell geometry
config	optional SGAnalysisConfig fields, except model (given by model_type)
materials	grouped material records, each with a unique name
sections	records with name and/or id, a declared material, and an optional orientation in degrees (0 when omitted)

Unknown fields are rejected.

One Authority per Field

Each model file format owns the data it can express; the manifest must not repeat an owned field.

Model file format	Owns (not allowed in the manifest)
abaqus	materials, sections
gmsh	nothing
swiftcomp, vabs	materials, sections, config, model_space, beam/shell geometry

sgdim and model_type are always manifest fields. When the model file also encodes them (SwiftComp and VABS headers), reading checks that they agree. Arguments passed to sgio.read() must agree with the manifest as well.

Sections and Mesh Elements

For a Gmsh model file, sections bind mesh physical groups to materials:

element -> entity -> physical tag -> physical name -> section -> material

A section record matches a physical group by name, falling back to id (the physical tag) when the name is absent or unmatched. Elements whose physical group matches no section — an auxiliary boundary group, for example — are not SG elements. The mesh-level field layout is in SG-on-Gmsh Serialization.

Writing

sgio.write(..., 'sg_manifest', model_file=..., model_file_format=...) writes the model file first, then the manifest without the owned fields. Model files can be written as gmsh, swiftcomp or vabs; sgio has no Abaqus writer. The manifest records the swiftcomp/vabs format version actually written.