OBJ

Definition: OBJ is a text-based 3D file format that Wavefront Technologies developed. It stores geometric data such as vertices (points), faces (polygons), normals and texture coordinates in a readable text format. OBJ has universal support and is a cross-platform exchange format.

In B2B mechanical engineering, OBJ is used for: CAD export for web viewers, 3D printing of spare parts, archiving of design data, data exchange between different CAD systems, and visualization in presentations and documentation.

Advantage: A simple, robust format. It works everywhere and will still be readable in 20 years.

English: OBJ, Wavefront OBJ German: OBJ-Format, OBJ-Datei

Technical Structure

Text-based format

OBJ files are plain text files. You can read them in any text editor:

# Comment: simple cube geometry v 0.0 0.0 0.0 # Vertex 1 (point) v 1.0 0.0 0.0 # Vertex 2 v 1.0 1.0 0.0 # Vertex 3 v 0.0 1.0 0.0 # Vertex 4 f 1 2 3 4 # Face (face from vertices 1-4)

Advantage: Easy problem diagnosis (open the file in an editor), no proprietary binary format, future-proof (always readable).

Disadvantage: Larger files than binary formats (for example STL, FBX).

Geometric elements

OBJ stores this data:

Vertices (v): 3D points with X, Y and Z coordinates v 12.5 8.3 -4.2

Texture coordinates (vt): UV coordinates for textures vt 0.5 0.5

Normals (vn): surface normals for lighting vn 0.0 1.0 0.0

Faces (f): polygons made of vertices f 1/1/1 2/2/2 3/3/3 # Triangle (vertex/texture/normal)

Material file (MTL)

OBJ files refer to a separate MTL file for materials:

OBJ file: mtllib machine.mtl usemtl Steel_Housing

MTL file (machine.mtl): newmtl Steel_Housing Ka 0.2 0.2 0.2 # Ambient Kd 0.8 0.8 0.8 # Diffuse Ks 1.0 1.0 1.0 # Specular Ns 100 # Shininess map_Kd steel.jpg # Texture

Result: The OBJ file contains the geometry. The MTL file contains the appearance (colors, textures, reflection).

B2B Applications

CAD export for web viewers

OBJ as a bridge between CAD and the web:

Workflow: 1. Design in CAD (SOLIDWORKS, Inventor, Creo) 2. Export as an OBJ file 3. Import into a web viewer (Three.js, WebGL) 4. The customer looks at the machine in the browser

Advantage: Universal support. The customer needs no CAD license.

Limitation: No CAD parameters (only geometry), no assembly hierarchy (everything is "flat").

3D printing of spare parts

OBJ for additive manufacturing:

Use: Legacy machines without CAD data, a spare part is no longer available → 3D scan → OBJ → 3D print.

Workflow: 1. Scan the real part (3D scanner) 2. Convert the point cloud to OBJ 3. Open the OBJ file in slicer software (PrusaSlicer, Cura) 4. 3D print

Alternative: STL (simpler, but no colors or textures).

Archiving of design data

OBJ for long-term data storage:

Problem: Proprietary CAD formats (SLDPRT, IPT, PRT) can be unreadable in 20 years (the software becomes obsolete).

Solution: Also archive the geometry as OBJ.

Advantage: The text format stays readable, no software dependency, easy validation (open the file in an editor).

Best practice: CAD original + neutral format (STEP for parameters, OBJ for visualization).

Data exchange between CAD systems

OBJ as the common denominator:

Scenario: The customer uses CATIA, the supplier uses Inventor.

Problem: Direct conversion CATIA ↔ Inventor loses data.

Solution: Export as a neutral format (STEP for parameters, OBJ for visualization).

When to use OBJ instead of STEP: - Only the geometry is necessary (no editing) - For presentations/renderings - When the target system supports OBJ better (for example visualization software)

Visualization in presentations

OBJ for marketing and sales:

Use: Trade show presentations, product catalogs, technical documentation.

Workflow: 1. Export CAD → OBJ 2. Import into rendering software (Blender, KeyShot) 3. Create photorealistic renderings 4. Or: import into PowerPoint (3D model feature)

Advantage: The sales team needs no CAD, only OBJ + a viewer.

OBJ vs. Other Formats

OBJ vs. STEP (.stp, .step)

Criterion OBJ STEP
Geometry Polygon meshes Precise surfaces (NURBS)
Parameters ❌ None ✅ Full CAD features
Size Larger (mesh) Smaller (mathematical)
Use Visualization CAD editing

When to use which: OBJ for display, STEP for design.

OBJ vs. FBX

Criterion OBJ FBX
Animation ❌ None ✅ Full
Materials Basic (MTL) Extended (PBR)
Size Text (large) Binary (small)
Support Universal Autodesk-focused

When to use which: OBJ for static models, FBX for animated machines (motion sequences).

OBJ vs. glTF (.gltf, .glb)

Criterion OBJ glTF
Web optimization ❌ Not optimized ✅ Made for the web
Materials Basic PBR (realistic)
Compression None Draco, KTX2
Standard Legacy Modern web standard

When to use which: glTF for modern web viewers, OBJ as a fallback or when glTF is not supported.

OBJ vs. USDZ

Criterion OBJ USDZ
AR support ❌ Conversion necessary ✅ Native (iOS)
Platform Universal Apple-focused
Complexity Simple Complex (USD-based)

When to use which: USDZ for iOS AR Quick Look, OBJ for cross-platform use.

Workflow: CAD → OBJ → Web

Step 1: CAD export

In SOLIDWORKS/Inventor/Creo: 1. File → Export → select OBJ 2. Settings: resolution (polygon density), units (mm/m), create an MTL file 3. Run the export

Result: machine.obj + machine.mtl + textures/

Step 2: Optimization (optional)

For the web: polygon reduction with Blender/MeshLab: - The CAD export is often too detailed (millions of polygons) - Optimize for the web: 100,000-500,000 polygons - Tools: Blender (Decimate modifier), MeshLab (Quadric Edge Collapse)

Step 3: Web integration

With Three.js (a WebGL framework):

```javascript // OBJ Loader const loader = new OBJLoader(); loader.load('machine.obj', function (object) { scene.add(object); });

// MTL Loader (for materials) const mtlLoader = new MTLLoader(); mtlLoader.load('machine.mtl', function (materials) { materials.preload(); objLoader.setMaterials(materials); }); ```

Result: An interactive 3D viewer in the browser.

Limitations

No animations

OBJ stores only static geometry: - No joints, rigging or skeletons - No keyframe animations - No morph targets

Solution: FBX or glTF for animated content (motion sequences of machines).

No assembly hierarchy

OBJ is "flat": all parts are in one file: - No subassemblies - No hierarchy (parent-child relationships) - No joint information

Solution: The CAD assembly structure is lost. Only the visual representation stays.

Large files

Text format = much storage space: - Complex machine: 50-200 MB (OBJ) vs. 5-20 MB (compressed glTF)

Solution: Compression (ZIP) or conversion to glTF for the web.

Basic materials

MTL supports only simple materials: - Phong shading (outdated) - No PBR (physically based rendering) - Limited texture support

Solution: glTF for modern, realistic materials.

Frequently Asked Questions (FAQ)

Can OBJ files contain colors?

Yes, through the MTL file. Vertex colors: directly in the OBJ file (less common). Material colors: defined in the MTL file (standard). Textures: image files that the MTL file refers to. Example: map_Kd steel_texture.jpg in the MTL file refers to a texture image file. Best practice: Keep the MTL file and the textures in the same folder as the OBJ file.

Is the CAD export to OBJ lossless?

No, the conversion from NURBS (CAD) to polygons (OBJ) loses data. What is lost: parametric features (holes and threads are no longer editable), precise surfaces (NURBS → approximated polygon mesh), CAD metadata (material specifications, tolerances). What stays: the visual geometry (sufficient for display). Rule of thumb: OBJ for visualization, STEP for further CAD work.

Which software supports OBJ?

Almost all 3D programs: CAD: SOLIDWORKS, Inventor, Creo, Fusion 360, FreeCAD. 3D modeling: Blender, Maya, 3ds Max, Cinema 4D. Web/game engines: Three.js, Babylon.js, Unity, Unreal. 3D printing: PrusaSlicer, Cura, Simplify3D. Viewers: Windows 3D Viewer, macOS Preview, MeshLab. Universal: If software can handle 3D, it usually supports OBJ.

How do I convert OBJ to other formats?

Online tools: Aspose 3D Converter, AnyConv (for small files). Desktop software: Blender (free, all formats), Autodesk FBX Converter, MeshLab (open source). CAD software: SOLIDWORKS, Inventor (import OBJ, export as STEP/IGES). Workflow: Import the OBJ file into Blender → export as glTF/FBX/USDZ. Recommendation: Blender for full control and optimization.

OBJ or STL for 3D printing?

STL: Simpler, supported by all 3D printers, only geometry (no colors). OBJ: Supports colors (multi-material printing), normals (smoother surfaces), textures (in theory). In practice: STL is the standard for monochrome printing, OBJ for multi-color/multi-material printing (if the printer supports it). Recommendation: STL for standard 3D printing, OBJ when you need colors or textures.

Industry Standards and Specification

OBJ specification: - Wavefront OBJ File Format – official specification - MTL Material Format – material file specification

Alternative neutral formats: - STEP (ISO 10303) – CAD exchange format - IGES (Initial Graphics Exchange Specification) – legacy CAD format - glTF 2.0 – web-optimized 3D format - Collada (DAE) – XML-based 3D format

Tools and software: - Blender – open source 3D software with OBJ support - MeshLab – open source mesh processing - FreeCAD – open source CAD with OBJ export

3D file formats: - glTF – web-optimized 3D format - FBX – Autodesk format with animation - USDZ – Apple AR format - STL – 3D printing format - STEP – CAD exchange format

CAD and conversion: - CAD export – data export from CAD systems - 3D model – 3D modeling - Polygon reduction – geometry optimization - Mesh processing – editing of meshes - NURBS vs. polygons – geometry representation

Web visualization: - WebGL – 3D graphics in the browser - Three.js – WebGL framework - 3D product configurators – web configurators - Web-based CAD viewers – CAD in the browser - Progressive loading – optimized loading

Materials and textures: - MTL format – OBJ materials - PBR materials – physically based rendering - UV mapping – texture coordinates - Texture maps – diffuse, normal, specular - Shaders – material rendering

3D printing: - STL format – standard for 3D printing - Additive manufacturing – 3D printing technologies - Slicer software – print preparation - Reverse engineering – from 3D scan to CAD - Spare parts production – 3D printing on demand