3D INTERACTION ORIENTED OBJECT MODEL

Cheng Cheng and Jia Lu

Department of Computer Science, Beijing Institute of Technology

Haidian Zhongguancun South No.5 Street, Beijing, China

Keywords: Object Model, Human Computer Interaction, Virtual Manufacturing, Perception, Behavior.

Abstract: Human computer interaction (HCI) is the most urgent challenge to virtual environment based manufacturing

today. Traditionally VRML/X3D standards are used as the main object models in virtual environment (VE),

and collision detection serves as the exclusive perception mechanism in such an environment. It is observed

that these models are difficult to satisfy the requirement of 3D human computer interaction. This paper tries

to provide a new object model scheme for virtual assembly which is a typical virtual environment

application that has the most critical HCI requirements. The work of this paper includes introduction of

object scheme, new perception mechanism, and object behaviour abstraction. The provided object model is

applied and validated in virtual assembly prototype system.

1 INTRODUCTION

Virtual manufacturing (VM), which refers to virtual

environment based manufacturing, has potential

advantage for mechanical product design and

validation. It is essentially a kind of critical real-time

interactive 3D graphical computing, with the most

urgent HCI requirement.

(Drieux et al. 2006) discussed the need of shape

adaptation for virtual environment applications and

gave a description of the process that is used to

acquire the models. (Figueiredo 2007) briefly

reviewed the collision detection algorithms used in

virtual assembly. From this paper it can be

concluded that collision detection is still the unique

perception method used in VM. (Seo et al. 2004)

discussed the object model for virtual environment,

and used state chart to define the object’s discrete

event and behavior. (Lee et al. 2002) gave a

behavior design method in virtual environment for

game and animation, but the behaviors still referred

to predefined motions as the same as the “route” in

VRML/X3D model. (Callison 1995) presented the

time-sensitive object (TSO) model structures

systems making object values extend to object

histories in which a sequence of time-constrained

values describe the evolution of the object over time.

(Pons 2002) proposed a method that promoted and

incorporated temporal constraint specifications to

the class/type-level in a compatible fashion with the

object-oriented framework. (Shoyo et al.) studied

how to abstract human’s motion. The author

discussed a primitive motion, whereas complicated

object behavior abstraction had not been

investigated.

2 STATIC CONTENTS OF

VIRTUAL OBJECT

The fundamental static contents of virtual object

should be constructed in advance. The objects in

manufacturing are initially formed by features, but

these features are not used in virtual environment

because the data models used by the design

environment and the virtual environment are quite

different. 3D interaction oriented virtual object in

figure 1 shows four static aspects of the virtual

object which abstract all the necessary data for

dynamic mechanisms.

Instead of only using VRML/X3D models in VE,

the authors retrieved geometric features through

parsing the STEP files and reconstructed a

description of the part and the features. The

interaction oriented attributes for both the part and

the feature include the shape type, the dimensions

and some auxiliary features, such as ‘Origin’, which

refers to the barycenter of the object; ‘Major’,

‘Minor’, and ‘3thAxis’, which refer to the

perpendicular axes of the local coordinate of each

393

Cheng C. and Lu J. (2010).

3D INTERACTION ORIENTED OBJECT MODEL.

In Proceedings of the International Conference on Computer Graphics Theory and Applications, pages 393-396

DOI: 10.5220/0002825103930396

 SciTePress

object. These attributes are retrieved for both part

itself and some of the assembly features of the part.

The feature class definition thus is given in the

object model.

The VRML shape node is linked with the object,

and mappings between the features and different

segments of the VRML shape surfaces are also

constructed. We use VRMLref as a reference to the

VRML file of an object. A set of auxiliary features

for every geometric feature are established and the

corresponding appearances are VRML shapes

referenced by AuxFeaRefs.

Direct manipulation in VE demands a real-time

constraint perception and satisfaction. Constraints

are considered as properties of objects and forced on

features. The constraint objects are claimed in the

virtual object. One object makes reference to another,

and the constraint dependency relationships form a

DAG (Directed Acyclic graph). Fast searching and

tracing is so important that constraint dependency is

explicitly specified as a relationship in the composite

object model, i.e., assembly model.

Figure 1: The framework of static description of virtual

object class.

As behavior contains much technical information,

recording the object’s behaviors has a great

significance in virtual manufacturing. Behavior is

abstracted and formalized as a trace. All the

participant’s manipulation will finally transited into

object’s behavior. For the sake of succinctness, the

behavior formalization is laid in next section.

Class VirtualObj basically gives a template

because every application has its specific data

requirements. The researchers should give a concrete

definition of every attribute in the field based on

their specific application and also make efforts to

acquire the attributes from the original design.

3 CONSTRUCTIONS OF

PERCEPTION AND

BEHAVIOUR

The most difficult work in 3D interactive system

construction is to design the dynamic characteristics.

It mainly depends on designer’s experience currently.

It is necessary to put forward new perception and

behaviour mechanisms for virtual object.

3.1 Mechanism of Perception

The computing based perception mechanism

provides to users with the space relationship

consciousness to facilitate object manipulating and

semantics producing. The strategies of searching all

the potential target features are designed. A series of

rules of creating some spatial relationships are

established. The rules are formed which specify

when and how the special semantics are established

and the object transit among states. Every kind of

domain specific determining algorithm is given.

These algorithms are linear and domain dependent.

Representations of all kinds of the perceptions are

devised. The spatial relationships are built step by

step.

Figure 2 shows the example of coincidence

constraint perception. This perception works to

sense the align constraint that user want to add.

After the matched feature pair has been found,

shown as the highlighted hole, Coincidence

perception is working. The ‘Major’, ‘Minor’ and

‘3thAxis’ of the matched feature pair are determined

as the potential feature set, shown as the red dashed

lines. Spatial relationship rule is like: (Rule 1)

Parallel relationship is true if one of the ‘Major’,

‘Minor’ and ‘3thAxis’ of the current feature is

parallel with one of the ‘Major’, ‘Minor’ and

‘3thAxis’ of the target feature; The domain specific

algorithm can be described as: let v

, v

are

respectively the vectors of axes of current feature

and target feature, the formula of judging the

coincidence constraint in the interactive process is as

equation 1, and the visual communication is defined

as highlighting the coincident auxiliary feature pair.







cos

(1)

Class VirtualObj

{

// The static part of the class

// Other dynamic parts below

… …

}

Attribute

descri

tion

Feature class definition

Constraint class definition

Trace definition

;

VRMLRef: VRML

AuxFeaRef Set

;

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394

Figure 2: An example of coincidence perception.

3.2 Behavior Construction

Object traces are constructed during the human

computer interaction process and interpreted and

simulated when the operations are required to repeat.

Definition 1: (Temporal behavior segment)

Temporal behavior segment (tbs) is a basic cell of

object behavior, has the form: <t

,cn

start

,bhv

end

>. Let BHV be set of the primitive object

behavior type set

，

CN be a constraint set, T be the

time set. Where t

T is the start time of the behavior

segment, bhv

BHV is a primitive behavior type,

start

CN is an original constraint, cn

end

CN is the

terminate constraint.

Behavior segment above is used to specify the

flow transitions. Here the typical behavior types

mainly include translation (Trans) and rotation (Rot).

The constraint types mainly include ‘Point’, ‘Line’,

‘Plane’, ‘Sphere’, ‘Circle’, ‘Distance’, and etc.

Definition 2

：（

Short behavior sequence

）

Short

behavior sequence (sbs) is a sequence made up of

three temporal behavior segments which are

respectively corresponding to feature-matching

perception, coincidence constraint perception and

face-mating perception, has the form: tbs

;tbs

The notation ‘;’ expresses the sequential

operation between two temporal behavior segments.

Short behavior sequence is an abstract of the

assembly operation from the domain. In order to

simplify it, translation motion and rotation motion

are separated apart, that is, when translation is

executed, the degree of rotation freedom is frozen

and vice versa.

Definition 3: (Object trace) Object trace (otrace) is

a successive short behavior sequences from an

initial state to a terminate state, it has the form:

sbs

;sbs

;…;sbs

Object behaviour is used to formalize the user’s

operation. In this way, the user’s direct manipulation

is translated into object’s behaviour when an object

is manipulated. The expert’s knowledge is thus

embedded into the object and guides the object to

simulate the human operations in a similar

circumstance. From the object’s assembly trace, we

can easily reverse or repeat the assembly process at

any time.

4 THE EXPERIMENTS AND

ANALYSIS OF 3DIOOM

MODEL

The authors conducted experiments to validate the

provided 3D interaction oriented object model

(3dIOOM). The first aspect is about semantics

construction. IOS represents the metric of system

capability of semantics construction. The second

aspect is about perception performance and behavior

capability. IOB represents the metric of perception

and behavior. The last aspect is interaction load.

IOC represents the metric of total cognition load.

The hardware the authors used is PC machine

and Logitech 3D spacemouse. The software platform

used is Open Inventor 5.0 and Microsoft Visual C++

6.0. A gear case which includes 36 parts is used as

an example for verifying and validating 3dIOOM.

Three models: 3dIOOM, VRML/X3D with AABB

algorithm and VRML/X3D with K-DOP algorithm

are compared because most of the applied models

have the same complexity with them. There were 27

participants. All are regular students at Beijing

Institute of Technology. The participants were

randomly divided into three 9-member groups for

the three experiments respectively. The task is to

assembly 35 parts on the gear case in the virtual

workshop. The metrics are formalized and all values

are normalized in 10 scales. The discrete events and

the evaluated indexes are counted by the programs.

The experiment results are shown by Figure 3.

On the aspect of semantics, 3dIOOM model can

create 8 relationships, i.e., approaching, feature

matching, aggregation, constraint dependency,

coincidence, face mating, and two traces, while

other models only create a collision.

On the aspect of perception and behavior, the

perception efficiency and behavior capabilities on

representation, adaptation are compared. Perceptions

used in 3dIOOM model are real-time. The behavior

mechanism put forward in this paper can make

behavior be constructed directly from participant’s

direct manipulation while others cannot. The

behavior in 3dIOOM is adaptable to the changed

environment, while the behaviors in other models

can not have this capability.

On the aspect of HCI supporting, the cognitive

load in 3dIOOM comes from the sensing of feature

matching searching, coincidence and the face mating.

On the contrary, in models of VRML/X3D

combining with AABB or K-DOP, the load comes

from collision events which occurred a lots of times.

3D INTERACTION ORIENTED OBJECT MODEL

395

IOC(num)

3dIOOM VRML/X3D(AABB) VRML/X3D(K-DOP)

100

IOB(num)

3dIOOM VRML/X3D(AABB) VRML/X3D(K-DOP)

100

100 100

IOS(num)

3dIOOM VRML/X3D(AABB) VRML/X3D(K-DOP)

100

100100

(a)Semantics (b) PerceptionandBehavior (c) Cognitiveload

Figure 3: Experiment results of virtual object model.

5 CONCLUSIONS

The authors put forward an object model 3dIOOM to

promote HCI in VE. It can be clearly depicted by the

static and dynamic parts. New perception and

behavior mechanisms in VE are established. The

experiments showed that 3dIOOM model can well

support 3D direct manipulation in VE. The

disadvantages of this model lie in the difficulty of

reconstructing the feature based design information.

The current situation is a semi-automation process.

ACKNOWLEDGEMENTS

This paper is jointly supported by national science

foundation of China (No.60773046), the state key

lab foundation of China under grant No.

SYSKF0905 and Beijing key discipline program.

REFERENCES

G. Drieux, J-C. Leon, F. Guillaume, N. Chevassus,

October 4-6, 2006. Integrating Design with

Downstream Applications through Product Shapes

Adaptation Processes, IMACS Multiconference on

"Computational Engineering in Systems

Applications"(CESA), Beijing, China.

Mauro Figueiredo, July 2007. Adjustable approach for

collision detection in virtual prototype environments,

Geometric Modelling and Imaging (GMAI'07), Zurich,

Switzerland, 4-6.

Jinseok Seo and Gerard Jounghyun Kim, Jun, 2004.

Explorative Construction of Virtual Worlds: An

Interactive Kernel Approach, Proceedings of the 2004

ACM SIGGRAPH international conference on Virtual

Reality continuum and its applications in industry,

Singapore.

Gun A. Lee, Gerard Jounghyun Kim, Chan-Mo Park,

November 11-13, 2002. Modeling Virtual Object

Behavior within Virtual Environment, VRST’02, Hong

Kong.

H. Reibecca Callison, July 1995. A Time-Sensitive Object

Model for Real-Time Systems, ACM Transactions On

Software Engineering and Methodology, Vol .1, No 3, ,

Pages 287 -317.

Alexander P. Pons, July 2002. Temporal Abstract Classes

and Virtual Temporal Specifications for Real-Time

Systems, ACM Transactions on Software Engineering

and Methodology, Vol. 11, No. 3, Pages 291–308.

Shoyo Hyod，Kouhei Ohnishi，A Method for Motion

Abstraction Based on Haptic Information

Directionality and An Application to Haptic Motion

Display System，Accepted for publication in a future

issue of IEEE Transaction of industrial electronics.

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396