How to convert Open CASCADE
to glTF?

In solid modeling and computer-aided design, boundary representation—often abbreviated as B-rep or BREP—is a method for representing shapes using the limits. A solid is represented as a collection of connected surface elements, the boundary between solid and non-solid.

Boundary representation of models are composed of two parts: topology and geometry (surfaces, curves and points). The main topological items are: faces, edges and vertices. A face is a bounded portion of a surface; an edge is a bounded piece of a curve and a vertex lies at a point. Other elements are the shell (a set of connected faces), the loop (a circuit of edges bounding a face) and loop-edge links (also known as winged edge links or half-edges) which are used to create the edge circuits. The edges are like the edges of a table, bounding a surface portion.

Compared to the constructive solid geometry (CSG) representation, which uses only primitive objects and Boolean operations to combine them, boundary representation is more flexible and has a much richer operation set. In addition to the Boolean operations, B-rep has extrusion (or sweeping), chamfer, blending, drafting, shelling, tweaking and other operations which make use of these.

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.