SimLab IGES Importer for Modo — Seamless CAD-to-3D Workflow

Streamline Modo Imports: SimLab IGES Importer Tips & Best PracticesWorking with CAD data in a polygonal modeling and rendering environment like Modo can be rewarding — but only if the import pipeline preserves geometry, hierarchy, and metadata while minimizing cleanup work. The SimLab IGES Importer for Modo is designed to make that transition smoother. This article covers practical tips and best practices to get cleaner imports, reduce manual fixing, and maintain a predictable workflow from CAD to Modo.

Why IGES imports are tricky

IGES (Initial Graphics Exchange Specification) is a widely supported format for exchanging 3D CAD data, but it’s not inherently polygonal — it often describes NURBS surfaces, trimmed surfaces, and topology suited for CAD kernels. When converting to Modo’s polygon-based environment, issues commonly arise: non-manifold edges, duplicated geometry, inconsistent normals, disconnected parts, overly dense tessellations, and lost layer or naming information. Understanding these pitfalls helps you use the SimLab importer more deliberately.

Prepare the IGES file in the CAD system (first and most important step)

1. Clean geometry before export

   • Remove small features (fillets, tiny holes) that aren’t needed for visualization.
   • Heal gaps and overlaps between surfaces.
   • Delete unused construction geometry and sketches.

2. Simplify the model

   • Suppress or remove hidden details and internal components not visible in final renders.
   • Replace complex assemblies with simplified placeholders where appropriate.

3. Export options

   • If your CAD app supports IGES options, choose higher-precision or adaptive tessellation settings to preserve surface fidelity.
   • Export with hierarchy and layer/property information enabled if possible.

4. Use step/STP where appropriate

   • If the receiving pipeline supports STEP and preserves more metadata, consider exporting STEP as an alternative; but if IGES is required, follow the other prep steps rigorously.

SimLab IGES Importer: key settings to understand

• Tessellation/meshing controls: dictating how NURBS surfaces convert to polygons. Look for options like maximum chordal deviation, maximum edge length, and angle-based controls. Lower deviation gives smoother surfaces but denser meshes.
• Normal smoothing / hard-edge detection: controls whether edges are split or smoothed based on angular thresholds.
• Merge/cleanup options: remove duplicate vertices/faces, merge coplanar faces, and weld near-identical vertices.
• Layer and naming import: preserve original part names and layers to keep scene organization.
• Material/property mapping: import per-part materials or colors so you can quickly assign shaders in Modo.
• Import units and scale: ensure the importer’s units match your Modo scene to avoid scaling errors.

Recommended import workflow in Modo

1. Start a clean Modo scene and set the same units as your CAD file.
2. Import via SimLab IGES Importer with a copy of default settings — don’t overwrite your main settings yet.
3. Use conservative tessellation: aim for the coarsest mesh that still captures silhouettes and critical curvature. Example starting values: chordal deviation = 0.01–0.1 units (adjust depending on model scale); max edge length = 1–10 mm for product-scale models.
4. Enable “merge duplicate vertices” and “remove zero-area faces” to reduce immediate cleanup.
5. Preserve part names and layers to keep hierarchy and make it easier to isolate problematic regions.
6. After import, isolate large groups and check normals, face orientation, and scale.

Fast checks and fixes after import

• Normals and orientation

  • Display normals or use Modo’s Backface Culling to find inverted polygons.
  • Use “Reverse Polygon” on flipped faces or recalc normals where applicable.

• Duplicate geometry

  • Run vertex-weld or “Remove Duplicate” operations with a small tolerance.
  • Look for overlapping shells and boolean artifacts.

• Non-manifold edges and holes

  • Use selection by topology tools to find non-manifold edges and fill holes only where appropriate.
  • Consider converting problem regions to quads/clean topology manually or retopologize in sections.

• Mesh density and decimation

  • If the imported mesh is too dense, use Modo’s Mesh Cleanup or retopology tools to reduce polygon count while preserving silhouette.
  • Preserve sharp edges by using edge-weighted decimation or selective decimation.

• Materials and UVs

  • If materials imported as simple colors, convert them to Modo materials and set up PBR maps where needed.
  • IGES doesn’t store UVs; plan for UV unwrapping if texturing is required.

Troubleshooting common issues

• Warped surfaces or tessellation artifacts
  • Lower chordal deviation or increase max edge density on import. If that fails, re-export from CAD with tighter tessellation settings.
• Missing small features
  • Check export unit/scale and feature suppression in CAD. Tiny fillets/holes may have been removed during CAD cleanup or filtered out by importer tolerances.
• Broken assemblies and lost parent-child relations
  • Ensure hierarchy and layer export options are enabled in the CAD system. Some exporters flatten assemblies—if so, re-export parts individually and reassemble in Modo.
• Very slow imports or massive file sizes
  • Simplify and split the model into smaller parts; import only what you need. Use progressive tessellation: import coarse for layout, then re-import high-res for final renders.

Automation and batch imports

• Use SimLab’s batch conversion tools or scripts when you need to import many IGES files consistently.
• Standardize export/import settings across a team and store them as presets.
• Automate post-import cleanup (e.g., weld vertices, remove zero-area faces) using Modo’s scripting (Python) to reduce repetitive tasks.

Performance and hardware considerations

• Large CAD models with dense tessellations require RAM and fast storage. Keep working files on SSDs and use more RAM for viewport responsiveness.
• Use display-level decimation (if available) to keep viewport performance while maintaining high-res meshes for rendering.
• Consider using proxies or stand-ins for heavy geometry in complex scenes.

When to retopologize vs. keep CAD tessellation

• Keep CAD tessellation when:

  • You need exact surface fidelity for product visuals close to CAD intent.
  • You’re doing hard-surface modeling where CAD edges must be preserved.

• Retopologize when:

  • You need clean quad-based topology for animation, subdivision modeling, or organic adjustments.
  • The CAD mesh is overly dense, non-manifold, or full of tiny artifacts that disrupt shaders or subdivision surfaces.

Example presets (starting points)

• Lightweight preview:

  • Chordal deviation: 0.1 units
  • Max edge length: 10 units
  • Merge duplicates: on
  • Preserve names/layers: on

• High-detail product render:

  • Chordal deviation: 0.005–0.02 units
  • Max edge length: 0.5–2 units
  • Preserve curvature detail: on
  • Merge duplicates: on

Adjust these based on unit scale and project needs.

Checklist before rendering

• Confirm scene scale and camera clipping.
• Fix flipped normals and non-manifold geometry.
• Assign real materials and set up PBR maps.
• UV unwrap where necessary.
• Replace heavy parts with proxies if needed.
• Run a test render at low samples to verify shading and reflections.

Final tips

• Communicate with CAD modelers: agreeing on export conventions (units, layer names, suppressed features) saves hours.
• Keep import presets per project type and enforce them in a team pipeline.
• Prefer iterative imports: bring in coarse meshes for look development, then swap to high-res for final renders.
• Document recurring issues and their fixes so your team can apply consistent solutions.

If you want, I can:

• Create example SimLab IGES import presets tailored to a specific model scale (architectural, product, jewelry).
• Provide a short Modo Python script to automate basic post-import cleanup (weld vertices, remove zero-area faces, recalc normals).