=Paper=
{{Paper
|id=Vol-2533/paper30
|storemode=property
|title=The Analysis and Comparison of File Formats for the Construction of iOS OS Three-dimensional Objects for Augmented Reality Systems
|pdfUrl=https://ceur-ws.org/Vol-2533/paper30.pdf
|volume=Vol-2533
|authors=Dmytro Ostrovka,Taras Teslyuk,Peter Veselý,Ihor Prots’ko
|dblpUrl=https://dblp.org/rec/conf/dcsmart/OstrovkaTVP19
}}
==The Analysis and Comparison of File Formats for the Construction of iOS OS Three-dimensional Objects for Augmented Reality Systems==
https://ceur-ws.org/Vol-2533/paper30.pdf
The Analysis and Comparison of File Formats for the
Construction of iOS OS Three-dimensional Objects for
Augmented Reality Systems
Dmytro Ostrovka 1 [0000-0003-4818-3822], Taras Teslyuk 1 [0000-0001-6585-3715]
Peter Veselý 2 [0000-0002-7857-6355], Ihor Prots’ko 1 [0000-0002-3514-9265]
1Lviv Polytechnic National University, Lviv 79013, Ukraine
ostrovdi@gmai.com
2Comenius University in Bratislava, Odbojárov 10, Bratislava, Slovak Republic
peter.vesely@fm.uniba.sk
Abstract. The rapid development of three-dimensional technology in the mod-
ern world has also affected smart phones. An integral part of augmented or vir-
tual reality are the file formats for displaying three-dimensional objects. Since
there are more than a hundred of them, it is quite difficult to choose the most
suitable for concrete project. That is why in this topic most popular files for
displaying three-dimensional files have been chosen. In this work was analyzed
their properties and the stack of supported technologies, their ability to use it on
the iOS mobile platform, and also tested the opening speed of a particular for-
mat. During this work, an iOS mobile application was created to demonstrate
how to display three-dimensional models of compared formats. The result of
this work are the conclusions about the advantages and disadvantages of the
compared file formats, as well as the feasibility of using one or another com-
pared format to display three-dimensional models on the iOS mobile platform.
These conclusions can be useful to developers of mobile applications for the
iOS platform, which are faced with the task of using three-dimensional files in
their projects. They may help save time on choosing the most suitable format,
and the developed test application can serve as an example of the reflection of a
file in a mobile application.
Keywords: iOS, Fbx, USDZ, USDC, USD, Collada, Obj, Augmented Reality,
Virtual Reality, Mobile Development, AR, VR, Three-dimensional Files, 3d
Files.
Introduction
The role of smartphones in daily lives of modern people is increasing more every day.
At the same time, the market’s share of sales of Apple smartphones, which operate
exclusively on the iOS mobile platform, is 14.1% in the 1st quarter of 2019, which is
more than 54 million devices.
Copyright © 2019 for this paper by its authors. Use permitted under Creative Commons License
Attribution 4.0 International (CC BY 4.0)
2019 DCSMart Workshop.
Hence, the relevance of three-dimensional objects in the life of modern people is
higher than ever. The development of modern technologies is directed to bring the
computer world closer to the real one. Three-dimensional cinema or training with the
help of virtual reality is currently, no longer new.
All these trends have led to the active integration of three-dimensional objects into
such integral things for people as smartphones.
To work with three-dimensional graphics, which is quite complex, you need not
only high-quality hardware, but also an appropriate software base, a certain data
structure to store three-dimensional images.
Despite the high capacity of these technologies and the great prospect, there are
many solutions for storing and presenting three-dimensional graphics on the market.
However, some of them have restrictions in accordance with various platforms, they
are not available for developers, or even outdated or irrelevant. All this makes it diffi-
cult to interact with them and also requires developers to select the format, necessary
for their task and corresponding to the trends for displaying three-dimensional files.
The purpose of the article is to analyze and compare the file formats for building
three-dimensional iOS OS objects. Based on this comparison, iOS OS developers will
be able to choose a format for displaying three-dimensional files, based on new
trends, compatibility with other formats, openness, the availability of official docu-
mentation, and iOS-based user interface. All this will help reduce development time
for searching and studying all aspects of working with formats such as Obj [1], Fbx
[2], Collada [3] and USDZ [4]. The results obtained can be used to develop augment-
ed systems [5, 6] and virtual [7, 8] realities, in the process of developing smart home
systems [9, 10] and smart cities [11, 12] medical applications [13, 14], devices of
special [15] purpose etc.
1 Analysis of formats for saving three-dimensional objects
Due to its prevalence and widespread use in various industries, there are many file
formats for building and displaying three-dimensional files. All of them have their
advantages and disadvantages, the sphere of use, as well as the list of supported oper-
ating systems. Taking into consideration this, widespread formats were chosen for
building three-dimensional files that are suitable for use on the iOS mobile operating
system.
First, consider the Obj format. This is a geometry description file format first cre-
ated by Wavefront Technologies for their Advanced Visualizer animation package
[1]. This is an open file format, and it has been accepted by other developers of 3D
editors as standard. The full name of this format type is “Wavefront Object”.
The Obj format defines only the object’s geometry, the coordinates of each vertex,
its texture coordinates, normals and faces, which are defined by lists of polygon verti-
ces. The vertices of the polygons are, by default, set counterclockwise, making explic-
it definition of normals to be optional.
The advantages of this format include the ease of structuring data relative to other
compared formats. Also, the relevance of its use, is the support by many software
3
tools for creating three-dimensional models. However, the relative simplicity and
small file size are made up for the lack of animation, scene information, and the pos-
sibility of layering textures.
Next, consider the Fbx (Filmbox) format. This technology and file format were
developed by Kaydara and is currently owned and continues to be developed by Au-
todesk [2]. This format is used to ensure the compatibility of various three-
dimensional graphics programs. Fbx is a proprietary undocumented format. Today,
there are two file formats of Fbx: binary and ASCI.
The advantages of the file include support for animation, scene information and
texture layering. That is why the format is widely known in the film industry and
video games. Also, this format makes it possible to optimize the costs of developing
models with Autodesk3D animation software such as: 3DS Max, Maya 3D, Maya LT
and others.
However, the main drawback of this format is its closed nature and lack of official
documentation. Thus, for working with Fbx files, Autodesk forces developers to use
its own Fbx-Sdk library, which makes it possible to read information about a three-
dimensional model from an Fbx file.
Next, consider the Collada format (COLLAborative Design Activity). It is led by a
consortium of nonprofit technologies, the Khronos group [3].
Information about a three-dimensional object in this format is set using the XML
markup language; it increases the file size compared to the binary representation of
other formats.
The advantage of this format is the support of many functions, such as animation,
texture layering, the ability to save information about the scene. Also, a big benefit is
the availability of official documentation.
The main drawback of the format is the absence of common standards for creating
models. Together with the openness of the format, this causes a different approach to
data structuring and possible conflicts / artifacts when displaying them.
Last in this article, consider the USDZ format. This is a file format for storing in-
formation about three-dimensional files, developed by Apple and Pixar [4]. In fact,
this is an archive of USD files and their resources, such as: textures and files embed-
ded in the same type of USDZ.
USD (Universal Scene Description) - this is the first publicly available software
that solves the need for reliable and scalable, exchange and complement arbitrary 3D
scenes, which can consist of many elementary resources. [19]. Pixar uses USD as the
core of pipeline graphics in all of its 3D rendering applications.
USD files can be stored both in ASCII and in binary representation. Pixar positions
this format as a convenient language for creating and editing 3D data, and facilitates
the process of creating digital content.
The format is rapidly gaining popularity due to usability and good support. The
significant factor of interest in the format, among developers and designers, is that the
format is accompanied by the leading company for creating animated films - Pixar.
There is also an official set of tools, USDZ Toolset, for creating, editing and convert-
ing from other formats to the USDZ format.
This format allows you to structure information in such a way as to redefine indi-
vidual properties of primitives without creating a separate copy. This allows you to
reduce the file size compared to other formats and also to process the file faster.
Thanks to the support of nesting and links, files of this format are capable of scaling
and can also be divided into separate sub-files. This allows several designers to work
on the final model at the same time.
2 Comparison of file formats for displaying three-
dimensional objects
Since there is no single standard that would indicate the best way to describe the file
format for displaying the 3D model as a whole and specifically for the iOS platform,
it is difficult to make comparisons objectively. Therefore, first of all, you need to pay
attention to the requirements set in the project and the inherent functionality that has
to be present.
At the same time, the following research focuses on, criteria for evaluating various
formats, namely:
The support of file formats by mobile platform iOS.
The speed of processing and opening file formats for the iOS mobile platform.
A set of supported file format functions for displaying three-dimensional models.
2.1 The support of file formats by iOS mobile platform
Collada and USDZ formats are supported by the iOS mobile platform at the system
level. This means that for their reflection in the mobile application, developer does
not need to use third-party libraries or other tools and respectively this simplifies the
application’s development process.
In the case with the Obj format, iOS allows developer to read information about
the structure of models in this format using built-in tools. However, this does not
apply to additional .mtl files containing information about the colors and textures of
models. This, in turn, requires developers to create additional logic for the appropriate
mapping of models or the use of third-party solutions.
As far as the Fbx format is concerned, this file format is not supported at the iOS
OS level. In turn, Autodesk offers to use its own library for integrating the format into
the iOS mobile platform - FbxSdk. However, this library is not compatible with the
development environment for mobile applications for the iOS platform - XCode start-
ing with version 10.0 (as of November 2019, the latest version is 11.2.1) [16]. A pos-
sible solution for porting a file to the iOS platform is the popular third-party library
AssimpKit [17]. However, during the research of displaying models using this library,
sometimes collisions or even premature termination of the program occurred, which
may negatively facilitate on the appropriateness of using this format when developing
a mobile application. So, there are ways to display files of this format for the iOS
5
platform despite the lack of system support, but they are quite risky and should be
compensated for by other advantages of this format for a specific task.
Therefore, from the point of view of convenience, working with Collada formats
and USDZ files will not require the installation of additional libraries, which in turn
saves the size of the final mobile application. If you use a third-party library
AssimpKit, we need to consider the fact, it was developed by a group of non-profit
enthusiasts who do not take responsibility for the reliability of this library.
2.2 Opening speed of file formats by the iOS mobile platform
Since each format of three-dimensional files structures information about a three-
dimensional model in different ways, the processing time for the same model will be
different, depending on the selected format. Because of this, a comparison of speed
was performed of the same models for selected formats.
Models for comparison were downloaded from https://free3d.com [18]. Since
among the compared formats, the Obj format does not support animation, two types
of comparison were carried out:
Comparison of the speed of opening models without animation of all formats.
Comparison of the speed of opening models with animation among the formats
Fbx, Collada, USDZ.
The comparison was carried out on two iOS devices, iPhone July 2016 release and
iPad Pro 11 "2018 release, with iOS operating systems version 13.1.2 (the latest ver-
sion as of September 2019).
To compare static objects, we selected a three-dimensional model of a military hel-
icopter (46538 polygonal elements) in the Obj format, which, using the FbxConverte-
rUI, Blender, and USDZToolset software, was converted to other comparable for-
mats. The following Table 1 gives the comparison results.
Table 1. Results of the opening speed of a static model in various formats
Format File Size (MB) Opening Speed (sec) Opening Speed (sec)
iPhone 7 iPad Pro 11’
Obj (natively) 4,5 0,39 0,25
Obj (AssimpKit) 4,5 1,05 0,86
Fbx 1,7 0,87 0,59
Collada 6,3 0,10 0,05
USDZ 5,0 0,53 0,40
USDC 2,6 0,47 0,27
To compare the model with the animation, a model of a warrior with a sword (3438
polygonal elements) of the Collada format was selected, after which, using the tools
mentioned above, the input model was converted to other compared formats. The
following Table 2 gives the comparison results.
According to the obtained results, the Collada format is the fastest to open. This is
primarily due to system-wide format support. However, you should pay attention to
the fact that models in this format take up more memory. This is due to the method of
structuring and storing information, not in binary form, which are in the case of other
compared formats, but in the XML markup language[20, 21].
When opening static files, the Obj format showed the second-best result. However,
to display complex models with different textures, during testing, the third-party
AssimpKit library was used. The experiments showed that in this case, the time costs
significantly increase and exceed all other compared formats, which makes such a
combination the least effective among all formats.
Table 2. Results of the speed of opening a model with animation in various formats
Format File Size (MB/KB) Opening Speed (sec) Opening Speed (sec)
iPhone 7 iPad Pro 11’
Fbx 677 KB 0,30 0,24
Collada 1,2 MB 0,03 0,02
USDZ 866 KB 0,37 0,26
USDC 327 KB 0,10 0,20
USDZ files are supported at the system level in the same way as Collada. Binary
and archived versions of USD files: USDC and USDZ, respectively, showed average
results in the research. The time difference between these types of USD files is due to
the fact that before processing USDZ, the format is previously unpacked. The archive
also contains all the textures, increases the file size, but also adds convenience when
working with the file, because all assets are stored in one place and it is easier to ma-
nipulate. Among the compared formats, USDZ is the only one that preserves assets in
this way.
Fbx files showed the worst temporary results. In addition, Fbx files were the worst
to convert. Also, during the comparison of various models, Fbx files often contained
artifacts or even were not displayed correctly at all, despite the fact that the conver-
sion took place using official software from Autodesk FbxConverterUI. All these
factors make Fbx files an outsider among the compared formats.
Thus, according to the received results of the opening speed of the compared three-
dimensional file formats, the Collada format is the undisputed leader, however, the
USDZ format should be considered through the approximate speed and the lower file
size, which will be useful when working with complex multi-polygon models.
2.3 Set of supported function formats
Although all compared formats support similar technology stacks, there are still dif-
ferences between them. They can significantly affect the appropriateness of using one
format or another when solving a specific problem. This section compares technology
supported by formats. Among them:
7
Description of model geometry using approximate and persistence meshes [22].
These technologies allow tessellation as well as precise coding of the geometry of
curved surfaces that did not deform with a change in expansion. The USDZ format
is also by default compatible with OpenSubdiv [23]. This is a set of libraries that
allows dynamic speed and smoothing surfaces.
Colors displaying. Usually they are represented by indicating the values of the red,
green and blue components ranging from 0 to 1. Collada, Fbx and USD also sup-
port Alpha Blending, which allows you to specify the fourth parameter for the col-
or - the alpha component. Possible values for it are from 0 to 1, where 0 is com-
pletely transparent and 1 is completely opaque.
Textures displaying. All compared formats support texture mapping. Collada, Fbx
and USDZ also support multitexture [24], which allows the simultaneous use of
two or more texture as a template for surface models.
Information about the scene. The Obj format does not contain scene information at
all. Other compared formats support storing information about the camera light and
relative position [25].
Models animating. Collada, Fbx and USDZ support keyframe animation. Their
implementation uses a sampler that describes how to manipulate the mesh using
splines depending on the time elapsed. In addition, these specifications contain in-
formation on how to scan using the algorithm, and how to use the information
stored in the respective nodes. According to Obj - this format does not support an-
imation.
File structure. File structure of the Fbx, Obj and USDZ formats can be stored both
in ASCII and in binary form. According to Collada - it uses the XML markup lan-
guage to store model information. In the case of the Obj format, the ASCII version
(.obj) is independent and the binary (.mod) is proprietary.
Documentation formats. Collada and UZD have a full official specification with
usage examples. Fbx only contains class documentation and methods for the Auto-
desk Fbx-Sdk library. Obj does not have any official specification, however, due to
the relative age of the format, there is a large number of independent, open sources.
The following Table 3 gives all the supported technologies of the compared formats.
Table 3. Supported technologies of the compared formats
Obj Fbx Collada USDZ
Approximate and
Supporting Supporting Supporting Supporting
persistence meshes
Colors and textures Supporting Supporting Supporting Supporting
Multitexture Not supporting Supporting Supporting Supporting
Scene information Not supporting Supporting Supporting Supporting
Animations Not supporting Supporting Supporting Supporting
File structure ASCI/Binary ASCI/Binary XML ASCI/Binary
Specification Third party Absent Official Official
So, considering the technologies supported by the formats, the most universal are
Collada and USDZ due to good documentation and openness. As for the Fbx format,
its main advantage among other formats is the large number of supported software
from Autodesk.
Conclusions
This article analyzes the common formats for displaying three-dimensional models on
the iOS platform, identifies their features advantages and disadvantages. In the course
of work on this article, a mobile application for the iOS platform was developed to
test methods for integrating file formats for building three-dimensional objects, name-
ly Obj, Fbx, Collada and USDZ.
After conducting a detailed analysis of each format, analyzing the spectrum of their
technologies, the support of iOS mobile platform, as well as practically exploring how
to integrate them on the iOS mobile platform, the following final conclusions were
drawn:
Obj format that supports the least technology stack. It is advisable to use it in pro-
jects where support for the scene or animation is required, and there is a need for sup-
port and consistent interpretation by various CAD software. It is supported by a large
number of modern software for three-dimensional modeling. Simple models of this
format are quite easy to display on the iOS mobile platform without using third-party
libraries.
Fbx is a common solution for working with three-dimensional files. This is primar-
ily due to the availability of a large number of software for creating models in this
very format. However, files of this format, are possible but rather problematic to dis-
play on the iOS mobile platform, due to the lack of support for the format at the sys-
tem level. Third-party solutions for integrating the format into projects for iOS, such
as AssimpKit, do not always allow you to reflect the models properly.
The format should be used in projects where the costs of converting to another
format exceed the costs of setting up the integration of the format and its proper re-
flection in projects for iOS. For example, when there are a large number of complex
three-dimensional models that need to be integrated into the project.
Collada is a large and complex format that supports many features. Although the
specification is a big plus when working with the format, the drawback is the lack of
common standards for creating models, which implies a different approach to data
structuring and possible conflicts / artifacts when displaying them. The format began
to lose its relevance with the advent and development of a more standardized Fbx file,
which makes its use in projects not promising and difficult to support in the future.
USDZ is the most convenient and relevant format for integration under the iOS
platform. It supports a wide range of technologies, as well as:
Contains built-in compatibility for smoothing surfaces using OpenSubdiv libraries,
which allows to optimize the size of models without losing the quality of their re-
flections.
Contains official documentation with examples of building elements.
9
The only one of the compared formats that allows several designers to work on the
same three-dimensional project without collisions in the files.
Optimizes file size using the built-in link system and virtual copies of primitives.
During testing, this format proved to be better for use in projects under the iOS plat-
form, both for displaying small static models and for manipulating several complex
and animated objects. It is easily ported to the iOS mobile OS, and the official USDZ
Toolset allows you to efficiently convert third-party formats that are not supported by
iOS to USDZ format.
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