The “.obj” format is one of the most important in both 3D printing and graphics applications. It is the preferred format for multicolor 3D printing and is widely used as a neutral exchange format for non-animated 3D models.
Therefore, in this article I will teach you in detail the OBJ file format and how it differs from other formats, such as STL in the case of 3D printing, or COLLADA and FBX in the case of graphic applications.
What is an OBJ file?
As far as is known, the OBJ file format stores information about 3D models. It was originally created by “Wavefront Technologies” For your application “Advanced Visualizer” to store geometric objects composed of lines, polygons, curves and free-form surfaces.
As such, OBJ files can encode the surface geometry of a 3D model, but can also store color and texture information. However, the format does not store any scene information (such as light position) or animations.
Additionally, an OBJ file is typically generated using CAD (computer-aided design) software as the final product of the 3D modeling process. The extension of this corresponding format is simply “.obj”.
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On the other hand, the OBJ file format is open source and neutral. Which is often used to share 3D models in graphics applications, this is because you enjoy good import and export support from almost all CAD programs.
In recent years, it has also become popular as a file format for multicolor 3D printing, as the standard 3D printing format “STL” does not support color and texture information.
Differences between the OBJ file and other CAD formats
Below I will show you some important differences between OBJ files and the other best-known CAD formats.
1. Use in 3D printing
The most dominant file format in the 3D printing world is “STL”. However, this STL file is a relatively old format that, although very popular, has not kept up with the times when it comes to updating.
On the other hand, 3D printing has made multicolor print has become more popular in recent years, (which STL is not supported), and the increasing precision of printers has also posed additional challenges for the STL format.
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Therefore, this one cannot handle high resolutions very well, as a higher resolution layout in the format comes with a significantly larger file size.
That is why OBJ files can approximate the surface geometry with the necessary precision without increasing the file size. This is possible using the curves of “Bezier” and a method called “NURBS”. Additionally, the OBJ file format has native support for multiple colors and textures within the same model.
Collectively, this file format has a substantial advantage over the STL format if you need accurate multicolor models. As time goes by, it is very likely that it will become more and more popular because of this.
Despite this, the OBJ file is not as universal as the STL format. Almost all 3D printers support STL, but the same cannot be said for OBJ, although it also enjoys reasonable adoption and support. Therefore, if you are 3D printing a monocolor model with a standard printer, the STL format is still preferable.
Both OBJ and STL formats have a very large ecosystem with a large and invested user base and many third-party tools. There are other 3D printing file format types, such as VRML, AMF, and 3MF, but they do not have comparable support and are not serious alternatives to the STL and OBJ file formats at this time.
2. Use in 3D graphics applications
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The most commonly used file formats in 3D graphics applications are OBJ, FBX and COLLADA. The most important difference between the OBJ file format and others is the support for scene information (such as light sources) and animations.
As you already know, OBJ does not support scene information or animations, while the “FBX” and “COLLADA” yes they can do it. Therefore, if you need animations for your game or movie, you had better use FBX and COLLADA formats.
3. Advantages between files
The OBJ file format is a simple, open format with extensive export and import support among CAD software. This means that if you share your 3D model as an OBJ file, it is very likely that other CAD software will interpret it correctly and consistently. The same cannot be said for the FBX or COLLADA formats.
The COLLADA format is also open source but is quite complicated, which makes different CAD programs interpret it differently and generate inconsistencies. On the other hand, the FBX format is a closed and proprietary format that offers a software development kit (SDK) to convert existing formats into FBX (Export).
However, it is not so easy to follow these guidelines (convert an FBX file to another format (Import). Non-CAD software developers “AutoDesk” They usually have to work their way around implementing a plausible FBX import, leading to inconsistencies.
Apart from the wide compatibility, OBJ files are much lighter than FBX or COLLADA files if they load with the same 3D model. This is due to the simplicity of the OBJ file format compared to other specifications and its native binary encoding.
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On the other hand, if you don’t need the full scene or animations and are concerned about compatibility and consistent interpretation between CAD programs, OBJ is the appropriate file format. In almost all other cases, FBX is the optimal format for 3D graphics applications.
4. Modern features of the format
In terms of modern features, FBX is the most progressive format. It offers many cutting-edge features with regular updates and improvements. The OBJ file format is second in terms of features, while the COLLADA format is considered slow to change.
OBJ File Features
1. Geometry
The main purpose of the OBJ file format is to encode the surface geometry of a 3D object, and in this sense it is quite versatile. Allows several options for encoding surface geometry.
can be applied “Tessellation” with polygonal faces, free-form curves and free-form surfaces. Let’s explore the pros and cons of each of these before moving on to questions related to 3D printing, file resources, and specifying the file itself.
2. Tessellation with polygonal faces
In its simplest form, the OBJ file format allows the user to tessellate (mosaics) the 3D model surface with simple geometric shapes such as triangles, quadrilaterals or more complex polygons. The vertices of the polygons and the normal to each polygon are stored in a file to encode the surface geometry of the model.
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On the other hand, tessellations with polygonal faces have advantages and disadvantages. Polygons are simple geometric shapes and this method is the simplest way to describe surface geometry. However, approximating a curved surface with polygons introduces coarseness to the model.
In the case of 3D printing, the models will be printed with the same coarseness as the file specifies. Of course, by making the triangles smaller and smaller, the approximation can be made better and better, resulting in good quality prints.
However, as the size of the triangle decreases, the number of triangles needed to cover the surface increases. This can lead to gigantic file sizes that 3D printing cutters have difficulty handling. It’s also a real pain to share or upload files as big as that.
Therefore, it is very important to find the right balance between file size and Print quality. But there is no point in reducing the size of your model’s triangles to the absolute extreme. At some point, you will get diminishing returns as your eye will not be able to distinguish between print qualities.
3. Freeform Curves
The OBJ file format also allows you to specify the surface geometry of a model using freeform curves. The basic idea is that the user defines a collection of free form curves (Cardinal Splines, Bezier curves, etc.) that run along the surface of the model. The surface is then approximated from this collection of curves.
Therefore, freeform curves are definitely more complicated than polygonal faces. But by sacrificing simplicity, we also gain a lot.
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Since freeform curves can describe curved lines exactly using a few mathematical parameters, they require much less data to describe the same surface compared to an approximate method such as polygonal tessellations.
So you can create a high-quality encoding of any 3D model using free-form curves without increasing the file size.
4. Freeform surfaces
With the OBJ file format, you can also specify the geometry of the surface by tiling the surface with free-form surface patches instead of simple polygons. This type of surface patch It is very useful for describing surfaces that are not like planes, spheres, cylinders or cones, surfaces that do not have a rigid radial dimension.
On the other hand, the most common freeform surface is called “NURBS” (Non-Uniform Rational B Spline), and the OBJ file format supports it.
The advantages of using freeform surfaces are somewhat similar to the advantages of using freeform curves: they are more precise and lead to smaller file sizes with greater precision than other methods.
In fact, one could argue that freeform surfaces are more precise than freeform curves, since they encode the surface exactlyinstead of approximating the surface using curves.
This is why freeform curves are often used in industries that demand absolute precision, such as aerospace and automotive design and engineering.
5. Color and texture
In many applications, the appearance of 3D models is of great importance. A racing video game, for example, with boring, colorless cars would be a much less exciting experience. For that you need to look at reality. The color and shine of a car are examples of properties related to appearance.
In simple terms, appearance describes the properties of the surface, such as the type of material, the…
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