How to convert glTF
to OBJ?

glTF is an open standard file format for 3D scenes and models. It's designed to be compact and efficient, making it easy to distribute and render 3D content on various platforms and devices.

glTF files contain information about the 3D scene, including geometry, materials, animations, and more. They can be used in different applications, from gaming and virtual reality to augmented reality and web-based 3D experiences.

Support of glTF in CAD Exchanger

CAD Exchanger can import and export glTF 2.0 files in binary (.glb) and text (.gltf) format. Such support includes:

• polygonal representations;
• assembly structure;
• names;
• colors, materials, textures;
• user-defined properties;
• PMI as polylines (export only).

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Pros of the format

Efficiency

All the basic data (vertices, triangles, normals, UV coordinates, etc.) are contained in binary form and can also be further compressed. Besides, the file structure is carefully organized to ensure that there is no extra or redundant data. Thus, the file contains only the necessary information to define the 3D scene, without any unnecessary clutter. By eliminating redundant data, glTF files become more lightweight and easier to process.

Cross-Platform Compatibility

It is an open standard supported by a wide range of platforms and applications. This allows for seamless integration between different software, making it easier to share and view 3D models across various devices. Whether it's a web browser, a virtual reality headset, or a mobile device, glTF ensures that your 3D content can be experienced on different platforms without any compatibility issues.

Cons of the format

Lack of Backward Compatibility

glTF has seen rapid development and improvements over the years, which means that older versions may not be fully compatible with newer software or engines. This can be a challenge if you are working with older files and need to use them in a newer environment.

Limited support of advanced features

For more advanced usage scenarios it may be important that this format has limitations in the areas of animation and lighting. In particular, there is inadequate support for keyframe animation with cubic interpolation, animation of rotation angles, and tension-continuity-bias animation curves. glTF also doesn't support lights and multiple attenuation models.

FAQ

What are the glTF file extensions?

glTF files typically have the extension ".gltf" or ".glb". The ".gltf" extension is used for the textual representation of the glTF file format. It is a human-readable JSON file that contains all the necessary information to define the 3D scene structure, including geometry, materials, animations, and more.

The ".glb" extension represents the binary version of the glTF format. It is a binary file that contains all the data, including the scene hierarchy, geometry, textures, and more, in a compact and optimized manner.

How to open an .glTF file?

To open this file, you will need a compatible software application, for example, CAD Exchanger Lab. Launch the software and navigate to the 'New file' option. Browse your computer's directories and locate the .gltf file you want to open. Then select it and click "Open". Once the import process is complete, the .obj file should be loaded into the software, allowing you to view and interact with the 3D model and associated data.

History of glTF format

This format was initially introduced by Khronos Group in 2015. The initiative aimed to create a common, royalty-free specification for efficient transmission of 3D content, with a focus on real-time applications and web delivery.

The first version, glTF 1.0, was released in 2015, providing a foundation for 3D asset transmission. Building upon the success of glTF 1.0, the Khronos Group released glTF 2.0 in 2017, which brought significant improvements and expanded capabilities. glTF 2.0 introduced a more efficient binary file format, enhanced support for physically-based materials, skeletal animations, and more advanced rendering features. It also introduced a clear separation between the JSON scene description and binary data, allowing for more efficient transmission and loading.

Since then, glTF has gained widespread adoption and support across the industry. Numerous software tools, engines, and platforms have embraced glTF as a standard for delivering 3D content. The format continues to evolve with regular updates and extensions, addressing new requirements and advancing the state of 3D content transmission.

The OBJ format is a popular and widely used file format for representing 3D geometry. It was initially developed by Wavefront Technologies for their Advanced Visualizer software. OBJ files store information about the vertices, faces, texture coordinates, normals, and material properties of a 3D model.

This format supports the representation of polygonal geometry, making it versatile for a wide range of applications. OBJ files are widely supported by various 3D modeling, animation, and rendering software, making it easy to share and exchange 3D models across different platforms and workflows.

Support of OBJ files in CAD Exchanger

CAD Exchanger can import files with external .mtl (material library) files, files with both multiple and single parts, and export files. Such support includes:

• polygonal representations;
• colors, materials, textures.

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Pros of the format

Universality

One of the key advantages of this format is its widespread compatibility. OBJ files can be imported and exported by a vast number of 3D modeling, animation, and rendering software applications. This broad support allows for seamless collaboration between different software packages, making it easier to share 3D models across various platforms and workflows. Whether you're working with industry-standard software or niche tools, chances are high that they will support the OBJ format.

Simplicity

The OBJ format is known for its simplicity and ease of use. OBJ files are plain text files, making them human-readable and easily editable. This simplicity makes it straightforward to manually modify or create OBJ files using a basic text editor if needed. Additionally, the file structure of OBJ is relatively straightforward, consisting of vertices, faces, and associated information. This simplicity makes it accessible for beginners and allows for quick understanding and integration with other software pipelines.

Cons of the format

Limited Geometry Support

This format has some limitations when it comes to representing complex geometry. OBJ is actually a polygonal format, so B-Rep is not supported as a class, neither for a simple cylinder nor for super-complex geometry. As a result, OBJ is not suitable when there is a need for B-Rep, and not polygonal meshes. This can be a disadvantage when working with models that require precise curved surfaces or complex mathematical representations.

Lack of Animation and Rigging Data

Another drawback of the OBJ format is that it does not inherently support animation or rigging data. OBJ files primarily focus on static 3D geometry representation and lack the ability to store information related to skeletal animation, rigging, and dynamic simulations. It also lacks several features like support for lights, LOD settings, and advanced materials. This makes it less suitable for complex animated scenes or character animations that require bone structures, joint deformations, or motion data.

FAQ

Is OBJ format specification publicly available?

Yes, it is. The OBJ file format specification defines the structure and organization of OBJ files. OBJ files begin with a list of vertex data, which consists of coordinates (X, Y, Z) that define the geometry of the 3D model. Texture coordinates (U, V) can also be included to map textures onto the model's surfaces. Normal vectors (X, Y, Z) define the orientation of the surfaces.

Faces are defined using indices that reference the previously defined vertices, texture coordinates, and normals. Groups and smoothing can be specified to organize the model's faces and define the shading and smoothness of adjacent faces. Additionally, OBJ files can reference material libraries (MTL files) that define properties like color, reflection, and transparency for the model's surfaces.

What are the typical .obj file extensions?

The OBJ file format is usually associated with two file extensions: .obj and .mtl.

.obj is the primary extension for OBJ files. It represents the 3D geometry data, including vertex coordinates, texture coordinates, normal vectors, and face definitions. The .obj file contains the essential information required to represent the shape and structure of the 3D model.

.mtl is a companion file to the OBJ format. It contains information about the material properties applied to the surfaces of the 3D model, such as color, reflectivity, transparency, and textures. The .mtl file is referenced by the OBJ file to assign materials to different parts of the model.

How to open a .obj file?

To open this file, you will need a compatible software application, for example, CAD Exchanger Lab. Launch the software and navigate to the 'New file' option. Browse your computer's directories and locate the .obj file you want to open. Then select it and click "Open". Once the import process is complete, the .obj file should be loaded into the software, allowing you to view and interact with the 3D model and associated data.

History of the OBJ format

The OBJ file format has a rich history in the field of computer graphics. It was originally developed by Wavefront Technologies, a company known for its pioneering work in 3D computer graphics and animation software. The OBJ format was first introduced in the late 1980s as part of Wavefront's Advanced Visualizer software, which was widely used in the film and entertainment industry.

Wavefront designed the OBJ format to provide a standard way to exchange 3D models between different software applications. It aimed to address the interoperability challenges that arose due to the diverse range of 3D modeling and animation software available at the time.

As the OBJ format gained popularity, it became widely adopted by the computer graphics community. Its simplicity, versatility, and support for geometry, texture, and material data made it a favored choice for sharing 3D models across various platforms and software packages.

The OBJ format has been embraced by numerous 3D software applications, making it a de facto standard for exchanging 3D models. Despite the emergence of newer formats, OBJ remains widely used and supported due to its long-standing history, compatibility, and ease of integration into different workflows. Today, the OBJ format continues to play a significant role in the world of 3D computer graphics.