IGES-G(1)

iges-g reads an IGES (Initial Graphics Exchange Specification) file and writes the converted geometry to a BRL-CAD database.g file. The input is expected to conform to IGES version 5.3 or an earlier version.

With none of the -3, -d, -n, or -t options, the default action is to convert IGES solid model entities to their BRL-CAD equivalents. Type 186 manifold topology is constructed directly in OpenNURBS, including type 192 analytic cylindrical faces. Parameterized planes and cylinders retain their reference directions and authored parameter units (degrees for cylinder angles). Type 143 bounded and Type 144 trimmed surfaces are constructed as independent OpenNURBS faces and conservatively stitched into shared manifold topology when their boundary curves agree within the file tolerance. Trimmed surfaces may use the finite natural outer boundary of their base surface. Legacy type 108 bounded planes and their type 402 single-parent hole associations are also supported. Native CSG uses BRL-CAD primitives where representable. Supported general revolution and extrusion profiles use exact NURBS and primitive BRep callbacks; linear revolutions and circular extrusions retain native CSG when possible. All geometry and hierarchy are read from the same validated document. BREP objects are written as native BRL-CAD BRep objects by default; -m and -p select polygonal output by tessellating the validated OpenNURBS representation.

If a default import contains no bounded surface or solid entities, the converter imports its supported drawings and datums in model space without projecting them to XY. Unbounded construction planes do not prevent this drawing-mode selection. Non-planar curves and supported composite, conic, and parametric spline curves can be retained as adaptively sampled NMG wire geometry.

Surfaces of revolution retain their angular parameterization so their trims remain in the authored parameter space. Boundaries at surface poles may have parameter-space segments without corresponding model-space edges. Safe repair recognizes rounded poles, completes missing parameter-space sides at poles, and can match differently segmented boundaries using bounded geometric comparison while retaining the original model curves. Closed manifold edges retain their authored use orientation. Missing optional manifold parameter curves can be reconstructed from model-space boundaries in safe repair mode, starting at the source accuracy to preserve small features. Bounded parameter-loop endpoint repairs also apply to manifold faces. The initial repair allowance and the allowance for boundary recovery are the larger of 100 times the source resolution and 0.0001 times the local model-space boundary bounding-box diagonal. If no resolution is declared, 0.000001 mm supplies the source-resolution fallback. The bound uses the geometry being repaired, not the entire assembly, its distance from the origin, or the size of an untrimmed supporting surface. Initial pullback fitting still starts at source accuracy, and repairs exceeding the source-based allowance are flagged in the output and report. The default best-effort mode retries otherwise omitted bounded or trimmed faces individually. It first reconstructs parameter boundaries from the authored model curves, then tries adaptive parameter endpoint corrections if reconstruction fails. The adaptive pass can exceed the initial relative allowance while retaining the original model curves and supporting surface. It does not enlarge the tolerance used to stitch neighboring faces. Recovered faces must still pass OpenNURBS validity checks and periodic-domain checks. Their database objects carry iges.import_status=needs_review and iges.recovery attributes; adaptive repairs also record their tolerance. Warnings and the JSON report identify the source faces and recovery methods. Validity does not certify agreement between inconsistent source descriptions or make an open sheet a closed solid. Recovered periodic trims are placed inside closed NURBS surface domains; boundaries requiring unsupported seam splits are rejected.

After face recovery, retained bounded and trimmed faces are reassembled within their original source ownership groups, at the unchanged stitching tolerance. Closed connected components are oriented and recognized independently of unrelated open sheets. Closed shells with overlapping bounding boxes remain together, preserving possible cavity relationships and their relative orientation; the importer does not infer containment or force every shell outward. Disconnected open sheets are written as individual B-Reps beneath an uncolored, non-region combination retaining the aggregate’s name and source hierarchy references. Connected faces stay together rather than each becoming a separate B-Rep. Children have stable source-based names, and a uniformly colored sheet receives its own display color. Different colors within a connected sheet remain in per-face metadata; color boundaries do not split geometry. Plate thickness applies only to non-solid output. If reassembly or sheet extraction fails validation, the previously validated geometry is retained. Explicit manifold solids, including incomplete solids retained as invalid B-Reps, and void-shell relationships are not split into sheet combinations. Per-face metadata retains source IDs and recovery methods after regrouping. An object containing different recovery methods or tolerance bases records mixed in the corresponding object-level attribute.

Safe and best-effort import normalize trimmed-face parameter loops before assembly: outer loops run counterclockwise and inner loops clockwise in OpenNURBS parameter space. The surface geometry and its natural normal are unchanged. Normalizations are diagnosed and counted in the report. This avoids propagating incorrect face senses from otherwise valid clockwise outer loops.

These modes also check closed-shell orientation using bounded numerical integration directly over the trimmed surfaces. Isolated, closed, orientable shells are made outward-facing when the signed-volume estimate is well separated from zero and the oriented surface area cancels. This can reverse an entire inward shell or correct inconsistent face senses. Corrections are reported and recorded in iges.orientation_faces_reversed, without changing surface geometry or face provenance. --exact and --repair none leave the original face senses unchanged; --strict rejects a required correction.

Open, invalid, non-orientable, nearly zero-volume, and numerically inconclusive shells are left unchanged. Shells with overlapping boxes are also left unchanged: an inward shell inside another may be a legitimate cavity. Box containment is reported only as possible_cavity, not proof of containment. This diagnostic does not certify absence of self-intersections or validate Boolean assemblies. It does not depend on the cached OpenNURBS solid-orientation flag, tessellation, or ray-tracing acceleration structures.

For legacy bounded planes, safe repair can resolve an opposite plane-constant sign when all sampled boundary points support that interpretation within the nominal tolerance; the repair is reported without moving the boundary curves.

Default imports may be partial. The conversion summary counts omitted source geometry entities, and --report identifies their failures. Use --strict when omissions or repairs must cause the import to fail.

Long conversions print a progress message about every five seconds, including elapsed time, the current stage and operation, and the source entity where available. Geometry counts include processed source items, both retained and omitted; retries do not advance the count again. These counts are not an estimate of elapsed work or remaining time. Reporting continues during lengthy individual geometry operations. Short conversions do not incur a reporting delay.

An explicit type 186 manifold solid that cannot be reconstructed is retained by default as one invalid-solid BRep, containing its independently validated faces. An empty BRep preserves the identity when no faces can be rebuilt. The iges.shell_metadata attribute records outer and void shells, source face IDs, orientations, and which faces were retained. Such objects carry iges.import_status=invalid_solid and _brep_invalid_solid=1. They are not treated as plate-mode sheets, and validity checking and ray-tracing preparation reject them. Repair the intended solid topology before clearing the marker. Strict, exact, and polygonal output modes reject these incomplete solids.

The -3/-d drawing options and the -n/-t compatibility surface options are mutually exclusive. Both surface options use the direct B-Rep importer and retain native CSG members and their hierarchy. The output database may follow the input filename, as in iges-g input.igs output.g. The -o option overrides a positional output filename. Diagnostics identify unsupported or omitted geometry. To export geometry in the other direction, see g-iges(1).

brlcad(1), g-iges(1), mged(1)

The Initial Graphics Exchange Specification (IGES) Version 5.3, US PRO/IPO, September 1996.

BRL-CAD Team

This software is Copyright (c) 1991-2026 by the United States Government as represented by U.S. Army Research Laboratory.

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org