The development of augmented reality technologies has not bypassed mobile operating systems, in particular the iOS operating system. In turn, the three-dimensional file industry has a large number of ready-made solutions presented in various formats. However, not all of them are supported by mobile operating systems iOS, such as Obj or Fbx files. That's why the question of converting them to the supported by the operating system iOS formats, USDZ and Collada, is quite relevant. Accordingly, the paper analyzes the means of converting file formats for storing three-dimensional objects under the iOS platform. The results of an experimental comparison of the quality of converted threedimensional files make it possible to determine the optimal means for converting with minimizing deformations and losses. This, in turn, can help developers in choosing three-dimensional formats suitable for their tasks while working on an iOS product.
An empirical research method was used to achieve the goal. To find out the tools for file format conversion, three-dimensional models into supported by iOS, theoretical analysis of software for working with three-dimensional graphics was performed. The quality of conversion of each selected format was analyzed using experimental methods. 3
Since there are over a hundred different file formats for displaying 3D models, only the
most common ones that were not supported by the iOS mobile platform were selected.
That is, those file formats for which there are already many ready-made 3D models,
however, which cannot be displayed on iOS using built-in methods. According to
researches spent in this article [
Fbx - is a proprietary format that is owned by Autodesk. It is widely applied in the film industry and also in the industry of games, because of ability to keep animations and support of a wide set of programs for work with a 3D-graphics developed by company Autodesk.
Obj - an open format for storage of geometry of objects. This format can use textures or colours to display models. This format has received its popularity because of simplicity of creation and storage of models and also because of its openness.
The formats for displaying 3D files that are supported at the iOS level are Collada
[
Among the programs that are used to convert 3D models were those that allow to
convert Obj or Fbx formats to USDZ and Collada formats. Namely:
Reality Converter - Apple's application for converting Object models to USDZ
format [
It should be noted that all the above programs are free to download from official resources.
To perform analysis there was developed a test mobile application [
For testing were downloaded several 3D models from free3d.com resource [18]. The received results can be useful in the development of augmented reality systems [20, 21] health applications [22, 23], intelligent cities and smart home applications [24 – 26], etc.
At first the models of Obj type were considered. As "objects of this model do not contain animation". [5, pp. 326-327] so only the image quality of static files after conversion was evaluated. When converting to the USDZ format with the Reality Converter application, no collisions occurred and both models were displayed correctly, as can be seen in Fig. 1. It should be noted that this converter does not use a .mtl file that stores information about the color of objects, but allows overlaying textures. Blender also allows you to convert files to a USD-like format, namely USDC. The USDZ format is an archive that consists of one USDC file and a set of textures. The result of the conversion with Blender is a USDC file that describes the geometry and colors of the model, but does not have the texture representation, that can be seen in Fig. 2 of the sewing machine model.
Also, during the experiment, it was found that the final USDC file of Blender takes
more memory than the USDC file inside the USDZ file, which is the result of the
Reality Converter conversion.
When converting Obj files to Collada files using Blender, no collisions were detected,
as can be seen in Fig. 3, but the final size of the files has increased even more than the
previous conversions, as can be seen in Table 1. According to the research in the article
[
File name Iron Man Swing Machine
As you can see from the table and figures above, there is no best solution for converting Obj files to iOS compatible formats at the moment. Because you have to choose between converting the colors or textures of a model, and considering the size of the final model. However, USDZ is a new format that Apple is actively developing and improving, as evidenced by the availability of a new Reality Converter (released by Apple in January 2020) and increasing support for the format by third-party software (such as Blender), so it is possible that existing shortcomings will be corrected soon.
The Fbx format was discussed next. During the experiment, three different models were selected, two of which contained animation. To convert to USD-like formats, the Reality Converter and Blender programs mentioned earlier were used. During the experiment it was found that the latter (Blender) did not convert animation in the models and as a result USDС files did not contain animation.
It should be noted that some files were displayed either after conversion in Blender or Reality Converter. In other words, only one of the listed programs was able to correctly convert the model. This is due to the unique structure of each specific threedimensional model. Since Autodesk updates its Fbx plugins every year, such conflicts may occur due to different versions of these plugins during model development by the designer and conversion during the experiment. The results of the models converted from Fbx to USD-like files are shown in Fig. 4. ─ The first model with animation - was correctly converted by both programs. As it was said above, the animation model that was converted by Blender did not contain any animation. ─ The second model was correctly converted by Reality Converter. ─ The third model was converted only by Blender (without animation).
Fig. 4. Three-dimensional models converted from Fbx format to USDC (Z) format Blender and FbxConverterUI programs were used to convert to Collada format. Unlike the USD conversion result, the result of converting by Blender to the Collada format contains animation. However, during the experiment, there were some collisions after formatting the model as shown in the first model in Fig. 5.
As for the FbxConverterUI program, it often crashed. It is related to the outdated
version of the given program (last release 2013) and as consequence absence of support
of models on the basis of new versions of Fbx though it and official software from
company Autodesk. Also, the convertible models of this program deformed the distance
of the models from the center of the camera, so it was difficult to manipulate them. The
conversion results are shown in Fig. 6. The model of the dragon could not be converted
to the Collada format by any of the programs.
As with the conversion of Obj files, Reality Converter converts models with the
highest compression. This is primarily due to the USZD format the program converts
to. As researched in the article [
Based on the experimental results, it can be concluded that the optimal format for converting from Fbx to one that is compatible with iOS today is the format USDZ. This can be done with Reality Converter or Blender. However, during the experiment, it was found that the last one (Blender) does not allow saving information about the animation of the model being converted. Therefore, it is appropriate to use it in cases where the models do not contain animations or they can be ignored. This program should also be used when it is necessary to convert 3D models to the Collada format, because the alternative program FbxConverterUI may cause conversion failures. 4
Solutions that use 3D technologies to facilitate learning or to improve the quality of user interaction with the interface are appearing every day. Since smartphones are often the ones actively involved in the implementation of three-dimensional technologies, this paper examines the best solutions for porting three-dimensional models to the mobile OS iOS. Given that in the field of 3D graphics there are many available solutions that are not supported at the level of iOS, the actual means of converting them into formats supported by this OS. Common file formats for storing 3D objects, such as Obj and Fbx, have been chosen for this purpose. In order to analyze existing solutions, their problems and disadvantages for conversion of selected 3D formats into supported by iOS (USDC (Z) and Collada), several free programs were selected. These are: Reality Converter, Blender and FbxConverterUI. Using them, an experiment to convert formats on different models was conducted. During this experiment, a number of disadvantages and advantages of each program were revealed. According to the results, it was concluded that Reality Converter proved to be the most optimal program, as it allowed saving both animation and texture of models. However, it is also worth noting Blender for its ability to convert all types of comparable formats, although not always with the preservation of animation or textures of the model.
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