AC3D File Formats Explained — Importing & ExportingAC3D is a lightweight, flexible 3D modeling tool used in hobbyist and professional workflows for modeling, game asset creation, and visualization. One of its strengths is support for multiple file formats both for importing and exporting — allowing models created in AC3D to move smoothly between applications and engines. This article explains the most important formats AC3D supports, how to import and export them, common pitfalls, and best practices to ensure assets behave as expected across tools.
Overview: Why file formats matter
Different 3D applications and engines expect varying combinations of geometry, normals, UVs, materials, textures, object hierarchy, and animation data. Choosing the right format affects:
- Fidelity of geometry and shading (vertex order, normals, smoothing groups).
- Preservation of UVs and textures (essential for PBR workflows).
- Transfer of scene hierarchy and object transforms (useful for game engines).
- File size and simplicity (text-based vs binary).
Native AC3D format (.ac)
- Purpose: AC3D’s native format; best for preserving every AC3D-specific feature.
- What it stores: Geometry, materials, UVs, object hierarchy, transforms, and AC3D-specific attributes.
- When to use: When you plan to continue editing in AC3D or need lossless round-tripping.
- How to use: Save/Save As in AC3D. These files can be reopened with full fidelity.
- Caveats: Other 3D applications rarely support .ac, so export to a more universal format when sharing.
Wavefront OBJ (.obj + .mtl)
- Purpose: Widely used exchange format for static meshes and simple material assignments.
- What it stores: Vertex positions, normals, texture coordinates (UVs), faces, and a companion .mtl file for basic material properties (diffuse color, texture file references).
- Strengths:
- Very portable and supported by nearly all 3D tools and game engines.
- Text-based, easy to inspect and edit.
- Limitations:
- No animation, no complex material (PBR) or scene hierarchy; smoothing groups support varies.
- .mtl lacks modern PBR parameters (metalness, roughness).
- Best practices in AC3D:
- Ensure normals are correct and smoothing applied before export.
- Embed or copy texture files and update .mtl texture paths if needed.
- Triangulate meshes if target engine prefers triangles (some engines auto-triangulate).
- How to export: File → Export → Wavefront OBJ. Verify Export options (write normals, UVs, group/object split).
FBX (.fbx)
- Purpose: Feature-rich interchange format, commonly used for scenes, complex materials, and animations.
- What it stores: Geometry, normals, UVs, hierarchy, transforms, basic materials, skinning and animation (depending on exporter/importer).
- Strengths:
- Good for moving assets to game engines (Unreal, Unity) and DCC tools while keeping hierarchy and animation data.
- Supports binary form for compact files.
- Limitations:
- FBX is proprietary (Autodesk), and different implementations can vary; version compatibility may cause issues.
- Complex PBR materials may map imperfectly.
- Best practices:
- Bake transforms (apply scale/rotation) before export.
- Check FBX version compatibility in target tool (FBX 2013/2014/2018, etc.).
- Export animations and skinning only if AC3D model has them and target supports them.
- How to export: File → Export → FBX. Choose binary vs ASCII and select which data to include (geometry, materials, animation).
COLLADA (.dae)
- Purpose: Open interchange format for 3D assets with scene-level information.
- What it stores: Geometry, materials, textures, scene hierarchy, cameras, lights, and sometimes animation.
- Strengths:
- Open specification, useful for exchanging scene data across tools and some engines.
- Limitations:
- Support for advanced materials and PBR is inconsistent across apps.
- File complexity can lead to subtle compatibility issues.
- Best practices:
- Use for scene transfer where hierarchies and multiple objects need preservation.
- Test exported .dae in the target application immediately to verify material and transform fidelity.
STL (.stl)
- Purpose: Simple mesh format commonly used for 3D printing.
- What it stores: Triangulated surface geometry only (vertex positions, normals optional).
- Strengths:
- Extremely simple and widely accepted by slicers and 3D printing software.
- Limitations:
- No materials, no UVs, no hierarchy, no units metadata (some slicers assume millimeters).
- Best practices:
- Ensure the model is manifold and watertight before export.
- Export as ASCII or binary depending on downstream needs. Confirm units and scale.
- How to export: File → Export → STL. Check for options to write binary vs ASCII.
glTF / GLB (.gltf, .glb)
- Purpose: Modern, efficient format for real-time engines and web delivery (GL Transmission Format).
- What it stores: Geometry, normals, tangents, UVs, PBR material parameters (baseColor, metallic, roughness), textures, node hierarchy, animations.
- Strengths:
- Designed for runtime use: compact, supports PBR, binary (.glb) bundles resources into one file.
- Broad support in web viewers and engines (Three.js, Babylon, Godot, etc.).
- Limitations:
- Exporters must correctly map AC3D materials to glTF PBR parameters; some manual tweaks may be necessary.
- Best practices:
- Convert AC3D materials into PBR-friendly maps (albedo, metallic/roughness or a combined metalness-roughness map).
- Embed or externally reference textures consistently; use .glb when you want a single-file asset.
- Validate the exported glTF with a validator/viewer.
- How to export: Use AC3D’s glTF exporter if available, or export a compatible format (FBX/OBJ) and convert with tools (Blender, glTF exporters).
3DS (.3ds)
- Purpose: Legacy format originally for Autodesk 3D Studio.
- What it stores: Geometry, simple materials, UVs, and limited scene info.
- Strengths:
- Supported by many older tools and pipelines.
- Limitations:
- Outdated: 3DS has strict limits (e.g., vertex count per mesh, filename length, no support for modern materials).
- Best practices:
- Avoid for complex or modern workflows. Only use for legacy toolchains that require it.
Alembic (.abc)
- Purpose: Efficient interchange for geometry caches and complex animations (often used in VFX).
- What it stores: Time-sampled geometry, transforms, and arbitrary geometric attributes.
- Strengths:
- Excellent for transferring baked animations and large animated caches without skinning rig data.
- Limitations:
- Large files; not intended for editable rigs or procedural animation transfer.
- Best practices:
- Use when delivering baked simulations (cloth, particle caches) or frame-by-frame geometry to another DCC.
Importing: common steps & troubleshooting
- Check units and scale: mismatched units are a frequent source of size errors. If model appears huge or tiny, rescale or set units consistently.
- Apply transforms: reset or freeze transforms so rotation/scale do not carry over unexpectedly.
- Verify normals: incorrect normals can cause shading artifacts. Recalculate or flip normals as needed.
- Re-link textures: many formats store only filenames; ensure textures are next to the exported file or paths are corrected.
- Simplify materials: convert procedural or complex AC3D-only shaders to texture maps and basic material parameters for better portability.
- Triangulate when needed: some engines expect triangles — triangulate in AC3D or the target application to guarantee consistent face behavior.
Export checklist (quick)
- Apply transforms (rotation, scale).
- Recalculate normals and set smoothing groups.
- Ensure UVs are unwrapped and non-overlapping where required.
- Embed or collect textures into an asset folder.
- Choose format based on needs:
- Editing in AC3D only: .ac
- General mesh exchange: .obj (+ .mtl)
- Game engines / animations: .fbx or .glb
- Web/real-time PBR: .glb/.gltf
- 3D printing: .stl
- Test the exported file in the target application immediately.
Practical examples
- Exporting a textured prop to Unity: export as FBX (or glTF/.glb), include normals and UVs, copy textures into Unity Assets folder, set material shader to PBR and assign textures.
- Preparing a model for 3D print: ensure watertight mesh, scale to printer units, export as STL (binary preferred), and run a mesh repair tool if necessary.
- Publishing a web preview: export a glTF/glb with PBR textures, compress textures appropriately, and validate with a web viewer.
Troubleshooting table
| Problem | Likely cause | Fix |
|---|---|---|
| Model appears scaled incorrectly | Unit mismatch | Rescale or set consistent units before export/import |
| Shading looks odd / normals dark | Flipped or missing normals | Recalculate or flip normals; export normals |
| Textures missing | Paths not preserved | Place textures beside exported file; update paths in material file |
| Materials look different | Material systems differ (PBR vs legacy) | Bake maps (albedo/metallic/roughness), or reassign in target |
| Animation not present | Exporter didn’t include animation | Enable animation export, or use Alembic for baked geometry |
Conclusion
AC3D supports a broad set of formats allowing you to target 3D printing, game engines, web viewers, and other DCC tools. Choose the format that preserves the data you need (geometry, UVs, materials, animation), follow the export checklist, and validate exports in the target application. For modern real-time workflows prefer glTF/.glb for compact PBR-ready assets; for engine pipelines and animation use FBX; for simple mesh exchange use OBJ; and use AC3D’s .ac format for lossless round-tripping within AC3D itself.
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