Spacedesign: A Mixed Reality Workspace for Aesthetic Industrial Design

Michele Fiorentino Raffaele de Amicis Giuseppe Monno Andre Stork DIMeG, Politecnico di

Bari, Italy GRIS ,Universität

Darmstadt, Germany d.Dis, Politecnico di

Bari, Italy IGD A2,

Darmstadt, Germany fiorentino@dimeg.poliba.it ramicis@igd.fhg.de gmonno@poliba.it stork@igd.fhg.de

Abstract

Spacedesign is an innovative Mixed Reality (MR) application addressed to aesthetic design of free form curves and surfaces. It is a unique and comprehensive approach which uses task-specific configurations to support the design workflow from concept to mock-up evaluation and review. The first-phase conceptual design benefits from a workbench-like 3-D display for free hand sketching, surfacing and engineering visualization. Semi-transparent stereo glasses augment the pre-production physical prototype by additional shapes, textures and annotations. Both workspaces share a common interface and allow collaboration and cooperation between different experts, who can configure the system for the specific task. A faster design workflow and CAD data consistency can be thus naturally achieved. Tests and collaborations with designers, mainly from automotive industry, are providing systematic feedback for this on-going research. As far as the authors are concerned, there is no known similar approach that integrates the creation and editing phase of 3D curves and surfaces in Virtual and Augmented Reality (VR/AR). Herein we see the major contribution of our new application.

1. Introduction

Appearance and aesthetics of some commercial products (for example cars, ski boots, motorbikes) are as important as functionality for the success on the market. At the present time no software fully supports conceptual aesthetic design [15], and common practice in industry is to build physical mock-ups using rapid prototyping (RP) techniques, like stereo lithography or milling. During the review phase, adjustments and modifications are carried directly on the model, using traditional workshop tools. Subsequently, reverse engineering techniques update the changes into the original CAD data, ready as input for

new cycle. This trial-and-error method is clearly one of the biggest bottlenecks in the industrialization process. The drawbacks are represented by the amount of time to build physical mockups, cost, and especially the risk of misunderstanding and errors during the digitalization/reverse-engineering process. Moreover commercially available rapid prototype techniques do not provide in a short time the final look that is necessary for a feasible aesthetic evaluation. Ideally real time appearance assessment and modification would be extremely useful.

Figure 1. A car body is realized in Spacedesign using 3D devices and VR/AR visualization

Conversely the combination of virtual and augmented

reality technology allows intuitive sketching and modelling directly in 3D, integrating the creative and evaluation stages of the design process and minimizing the number of iterations [6]. 3D input and output devices together with form-descriptive gestures (to draw and manipulate models three dimensionally), have the potential to be more effective than the conventional methods because they give a superior perception and investigation of 3D shapes and models (figure 1) [7], [9].

This on-going research effort leads to the development of an innovative application for aesthetic styling: a VR/AR software tool called Spacedesign. Designers can materialize ideas in a configurable semi-immersive workbench-like workspace, using 3D input devices, and then keep the same settings, tools and environment for the design review, when a physical prototype is realized and augmented in real time for correction and changes. Both configurations -VR and AR- allow different skilled experts (Stylists, Designers, Engineers, Marketing dept.) to share a common model, whilst using personalized tools. Therefore Spacedesign provides a consistent mathematical representation of the digital model during the design workflow, from concept to mock-up review. Moreover CAD file standards are supported, for seamless integration with downstream applications (FEM, FEA) and manufacturing.

In the following, we discuss related work in section 2, an overview of the setup in section 3, software implementation in section 4 and details on the surfacing functions in section 5. Case studies are presented in section 6 and section 7 concludes the paper.

2. Related Work

One of the first systems that used 3D interfaces for free form modelling was 3Draw, developed by Sachs et al. [17]. In 3Draw a palette and a pen are connected to 6 degree-of-freedom (6DOF) tracking devices, and a normal monoscopic monitor is used for visualization. The orientation of the tablet forms a reference frame and the pen is the sketching tool for drawing curves directly in space. However, 3Draw cannot generate surfaces from the given curves.

Usoh et al. [23] experimented the Head Mounted Display for modelling surfaces in an immersive environment. In their collaborative modeller, hand gestures can directly deform surfaces according a physically simulated elastic behaviour. The drawback of this approach is the complexity of the calculations, which do not allow real-time interaction. Hummels et al. [13] examined the activities of automotive designers and suggested a two-handed gesture recognition interface in the Fishtank, a desktop on which the image of a stereo display is projected through a mirror. No implementation details and results are provided.

Conceptual Virtual Design System (COVIRDS) by Dani et al. [5] explores the multi-modal use of different input streams, like speech, gesture-recognition and 6DOF input devices for modelling. The user steps in front of a projection wall and can interactively modify the shape of the surfaces moving a set of control points previously selected with a virtual ray.

Wesche et al. [25] proposed a 3D styling system for free-form surface in a table-like Virtual Environment, called Responsive Workbench (RWB). A combination of

automatic and user-controlled topology extraction is used to generate surfaces form previously sketched curves. A variational approach is followed for the editing, and three virtual tools are provided: the smoother, the sharpener and the puller. Anyhow there is no explicit reference to the interactivity aspect of the interaction.

ARCADE [21] [22], acronym of Advanced Realism Computer Aided Design Environment, is a very useful and intuitive system for modelling surfaces on the Virtual table. It offers a wide set of different functions for surface creation: skin, coon patch, and net surfaces. During the sketching a simplified preview is also provided.

3DIVS by Fiorentino et al. [10] is a two-handed, gesture-based NURBS modeller in a semi-immersive environment. The workspace is composed of a stereo display, and two magnetic trackers connected to the Fakespace Pinchgloves for gesture recognition. Three different virtual tools, the Picker, the Twister and the Weighter, modify respectively position, torsion and weight of the control points lattice. The distance between the hands controls in real time the spatial influence of the tools.

De Amicis et al. [6] presented the 3D Eraser Pen metaphor that is a direct manipulative technique used to draw curves and surfaces. By means of this technique if the resulting polyline, curve or surface is not exactly what the designer wants, he/she can delete part of the sketch just going back and doing it again and again until he/she reaches the final shape. In that way the creation and deletion process are combined and rewriting the pencil and rubber metaphor in just one tool.

Dynamic Shader Lamps by Bandyopadhyay et al. [3] investigates the use of Spatially Augmented Reality to realize virtual painting and texturing over a real object. Projectors cast a beam over the physical model, which is optically or magnetically tracked. The system updates in real time the transformation matrix to keep the images onto the object during the movement. Colours and textures are easily applied by direct manipulation with a paint stylus. This interesting projection-based paradigm does not require glasses or heavy head mounted displays (HMD), which may be uncomfortable for the user, but as a drawback, shape modification and free form sketching can not be achieved by the system.

From the related work presented, it can be summarized that literature provides several VR/AR approaches to free-form aesthetic modelling. According our research, the current state of the art is not specifically developed for a proper industrial use, because it lacks of integration with the manufacturing process and support for multiple software\hardware configurations. In general, research work exploring the possibilities offered by Augmented Reality in strong conjunction with interaction in Virtual Reality for free-form surface modeling is still very rare. This paper gives a practical and substantial contribution in this direction.

3. Set up

Virtual and Augmented Reality hardware can be divided in three basic groups: visualization system, input devices and rendering engine. Each of the components in Spacedesign have been accurately selected for the specifying application, and to provide a “low-cost” investment, affordable even to small enterprises. UNIX-based VR at the moment offer better performances, but according to us the gain is not sufficient to justify higher complexity and price tag. Fortunately, performances in top-end graphical personal computers are getting sufficient for realize the so-called PC-VR, mainly thanks to the 3D game industry. Therefore we choose a Windows/PC solution for the rendering engine: a dual Xeon® workstation with ATI FireGL 4 graphic board.

In addition the system is independent from the visualization system: resolution, active/passive stereo, and camera position can be easily configured using ASCII text files to support CRT/LCD monitors, projectors and head mounted display.

The 3D input devices are easily handled by OpenTracker [12] library, which is developed to be a generic solution to the different tasks involved in tracking and processing data for virtual environments. OpenTracker provides an open software architecture based on a modular design and a XML configuration. We extended this library for the support of the ART dtrack [2] tracking system, and configured it for our specific set-up.

The system supports two interaction configurations, for two specific design tasks: concept creation and physical prototype review.

3.1. Setup for Concept Creation

For aesthetic design the ideal Virtual Reality visualization system should provide high quality images and a fair level of presence and immersion in the virtual workspace. In fact, during sketching and surfacing the visual feedback is fundamental for the perception of shapes. For this task Spacedesign uses a semi-immersive, table-like display (1.7 meters of diagonal), which allows conception e.g. parts of a car body in scale. The user wears a pair of tracked shutter glasses and his point of view is displayed in stereoscopic mode, so virtual objects appear three-dimensional, as floating in the air (figure 1). Moreover, being not fully immersive, more participants can gather around the screen and see gestures and interactions of others and discuss about the common model.

The cameras of the tracking system are placed in front of the user, about 2.5 meters from the ground and 1 meter from the table, thus covering the entire working volume (figure 2). This set-up allows a clear optical path between the user and the cameras during the normal sketching and working interactions.

Figure 2. Workbench Setup

3.2. Setup for Review

Review phase in Spacedesign means augmenting the physical prototype with computer generated images, realizing interactive adjustment of the model, annotations or visual appearance evaluations. For this task a pair of see-through Sony Glasstrom is used for displaying an augmented 3D stereo environment (figure 3). The glasses native resolution of 800x600 points is quite poor for the creation task, but sufficient for minimal changes and on-site evaluations. In fact, in this stage, only a small part of the design is modified and in a minor way. The user should move in the volume covered by the tracking system, that is 3x3x3 meters.

The RP is tracked and the virtual model can be overimposed. Each user should calibrate the system before the use, but the procedure is automated by the software using the line of sight method and takes only less than a minute to be accomplished [11].

Figure 3. Aumented Reality Setup

IR cameras

VR table

3.3. Input devices

Four tracked devices are used in Spacedesign: the glasses, the pen, the palette and the so-called “Navigator Axis” (figure 4). Magnetic Tracking systems are commonly used in VR, but they do not provide the accuracy and repeatability necessary for sketching precisely curves and surfaces. For this reason Spacedesign uses optical trackers, characterized by hight precision and accuracy. The requirement of keeping the line of sight always clear has been simply solved with a redundant number of cameras. A minimum number of three cameras allows full time tracking during all the common interactions. We dispose the cameras in front of the table, for a tracked volume of 3.5m x 3.5m x 1.5m. Being wireless, the user experiences the freedom of the interface in a very comfortable way. The pen is at the moment the only device that is tethered, but we are working to make it wireless using radio or ultrasound signals. The pen is realized using the micro switch of a serial mouse, and therefore is provided of 3 buttons. A detailed description of their use is described in the following section.

Figure 4. Workbench Setup

4. Implementation

Characterized by an open, modular architecture, Spacedesign is built upon Studierstube library [18], for the AR/VR interface, and ACIS [1] [4] as modelling kernel (figure 5). Studierstube is based on Open Inventor [24] and uses the so-called “Pen and tablet” metaphor for VR interaction: the non-dominant hand holds the transparent palette on which are displayed all the menus and buttons, the other handles the pen for application-related tasks [26]. Attributes in ACIS allow the extension of the internal data structure with user-defined information. Spacedesign uses attributes to realize a unified database, avoiding the redundancy of information between the mathematical and the simplified triangulation of the model, common in VR systems. In this way Spacedesign is ACIS-centred as shown in figure 6.

Figure 5. Software Architecture

Current functionalities of Spacedesign are shown in Table 1: basic 1D and 2D drawing commands for sketching, surfacing, editing, selecting and import/export industrial-standard file formats for integration with CAD/CAM applications. Many free-form functionalities are provided: skin, extrude, net, coon Patch, and piping. The Mirror function supports the design of symmetric elements, providing a real-time transparent feedback.

File 2D Surfaces Tools

Load-Save ProE Free Sketch Planar

surface Erase All

Load-Save Catia

Closed Free Sketch Extrude Erase

Selected Load-Save

Rhino Line Net Selection

Load-Save iges Polyline Skin Copy

Load-Save sat

Closed Polyline Coon Patch Move

Load-Save vrml

Nurbs Curve Pipe Mirror

Plane

Table 1. Spacedesign functions

4.1. Interaction

Interaction in VR/AR differs from traditional CAD because it uses 6DOF input devices, stereo vision, and real time manipulation. Therefore the whole application structure is different from the conventional CAD, in which each button on the screen is directly linked to a function of the kernel. The biggest challenge in the development of Spacedesign has been to provide the real time interaction during the surfacing operation. For this particular issue a specific architecture has been created. Figure 5 shows how the user interaction module works as separate layer in the application; it analyses and supports the user intention and provides an immediate visual feedback. The interaction for some computational-demanding tasks, like surfacing, uses completely different

routines from the modeller to achieve the required performance. The interface has been developed to be immediate and intuitive, while providing the user of a realistic representation of the created forms.

Figure 6. User interaction scheme

In virtual reality is difficult to communicate

informations to the user: floating messages or external object can be unfriendly and confusing. Following the idea of Windows-like applications, we decided to reserve a specific area of the virtual tablet called “Message Bar” for this task. Therefore, access to information is simple, and not intrusive in the virtual workspace. The Message Bar has different functions: guide step by step the user during the sketching, explain not allowed operations, and display error messages. Our tests have shown Message Bar very helpful, especially for beginners.

Moreover, Message Bar, buttons, and widgets lay-out on the virtual palette can be fully customized for each user, using a simple Open Inventor ASCII file. This allows to create a task-specific workspaces, i.e. surfacing tools for conceptual design and material/appearance modification for evaluation/review.

The interaction in Spacedesign is essentially bi-manual, with the dominant hand that holds the pen for sketching and surfacing, and the non-dominant is used for the manipulation of the other physical props, like the palette, the physical model, or the Navigator Axis. The first button on the pen near the tip performs the action of “doing”, like selecting, drawing, surfacing and 3Dbutton pressing. The second is used only in the skinning to terminate the drawing phase. Most of the functions need only one button press to be accomplished: i.e. to draw a free-hand curve the user press the button and keeps it pressed till the end.

4.2. Scene Navigation

Scene navigation is one of the most frequent actions during the creation and evaluation of the model. Virtual and Augmented reality allows natural immersion in the 3D scene because the virtual point of view is connected in real-time to the user’s head position. In some commercial CAD applications, coordinate axes are displayed on the screen, and can be used to change interactively the object’s position relative to the user. Similarly, we invented a 3D analogue of this widget, called “Navigator Axis”, by means of a transparent L-shaped tracked body permanently connected to the position and orientation of the modelling coordinate system (figure 4). The user can hold the Navigator Axis in his dominant hand for precise scene navigation or in the non-dominant hand as reference frame during the sketching phase. The shape of this physical prop allows immediate top, front and side view of the scene. We have experimented that users find particularly comfortable the navigator, especially during the interaction, because of the additional degree of freedom using both hands. The Navigator Axis is deactivated in the Augmented Reality setup, since the rapid prototype is registered and tracked in its place.

4.3. Real prototype tracking

This functionality is similar to the scene navigation, but with a different meaning. In this case the mock-up is tracked and his position is used to render the virtual image with the right position relative to the user, to provide the illusion of being superimposed over the real object. The navigation axis is disabled during this configuration. A precise calibration allows accurate overlapping of the virtual and the real object. At the moment the registration process is manual, by direct modification of an inventor ASCII file, but to simplify this task, we built a tracked transparent platform, with some references on it, for fast set-ups of small dimension models.

Figure 7. The tracking platform and a Ferrari model

4.4. Constrained 3D Manipulation

One of the major limitations in current virtual environment applications is the absence of constraints when interacting with digital objects. Precise movements in 3D space are difficult to achieve because of tracking errors and the natural vibrations of the human body. Constraints used in virtual worlds applications can be divided in two main categories: physical and virtual. Semi-immersive environments use real objects, which are visible to the user, as a reference for their movements. On the other hand, virtual constraints are software tools, which filter the 3D input according specific algorithms. Previous research has pinpointed the importance in VR based design software of the virtual tools for an effective user interaction [20] [8].

Spacedesign provides two different types of virtual constraints: geometrical and topological. The former helps the sketching intention limiting the position to a plane, a line or a 3D grid, the latter to a previously designed topological element: a vertex, an edge or a face. The metaphor of the laser ray is used to localize in the space the active position of the pen, and virtual constraints are displayed semi-transparent to avoid undesired occlusions of the working area (figure 8). From the implementation point of view, constraint are realized overriding the messaging system of Studierstube, which is based on the dispatching of Events, called So3DEvents. We developed a wrapper class called So3DEventCosnstrained to perform some reasoning of the 3D incoming input data, and dispatch a modified constrained event position. This solution is completely transparent to the modelling functions, which remain completely unmodified.

Figure 8. Planar Constraint

5. Advanced Surfacing

One of the key tasks during the aesthetic design process is sketching and manipulating 3D curves and surfaces. Effective techniques for specifying 3D curves or surfaces using 2D input devices have been extensively developed in commercial software, but the common

creation method is usually limited to planar curves which are extended to form surfaces. Consequently most of the traditional modelling kernel – ACIS included – are suited for a 2D interface and therefore are limited to this paradigm. Thus we developed free space surface creation functions for the specific 3D-native interface. Moreover most of the available tools use the control points (CP) for creating and editing, thus requiring a certain mathematical knowledge and experience to move the CP in order to obtain the desired surface. Spacedesign provides some intuitive modelling creation tools, and users can create freeform geometry from curves, surfaces, or measured data from real models (using the AR set up). Dynamic surface creation tools allow design changes to be explored interactively and immediately visualize the aesthetic/engineering implications of the design. Spacedesign surfacing functions are: skin, extrude, net, Coon Patch, and piping. In the following paragraphs we describe two surfacing tools: Interactive skinning and Coon Patch.

5.1. Interactive skinning

Skinning is one of the most used tools for free form generation: it fits a surface through a series of given profiles. ARCADE [22] presented this functionality with a simplified preview, but the discrepancy between the provided visual feedback and the final shape was frustrating for the designer. To overcome this problem, Spacedesign displays a consistent preview of the final surface (figure 9), using an optimized software architecture that minimizes the data flow between the modeller and the application, and an interactive mesh generator, which changes in real time the complexity of the tessellation.

Figure 9. Interactive skinning

5.2. Coons Patch algorithm

This is a simple tool for creating complex free form shapes in a intuitive way: a closed non self-intersecting contour is covered using a Coons patch [19]. The mathematical concepts behind the surface generation,

which requires four oriented curves for the interpolation, are completely handled by the application in a transparent way. The intuitiveness of the interaction method is reached by performing some reasoning on the input data: the outline of the 3D stroke is automatically splitted into two pairs of oriented curves. The resulting shape of the Coons patch heavily depends on the position of the split points. This function has been imported in Spacedesign from ARCADE [22] and improved to provide surfaces that better conforms to the user’s expectations. Starting form the splitting points using a simplified bounding box method, the algorithm searches in the respective neighborhoods relative maximum values of the first derivative along the curve. Using such points avoids undesired wrinkles, which appeared in the previous implementation. In addition, Spacedesign visualizes an approximate preview of the created surface during the sketching phase (figure 10).

Figure 10. The improved segmentation reduces the wrinkles in the Coon Patch Function

6. Case Studies:

The following hands-on applications show how Spacedesign can provide solutions to different industrial design and manufacturing problems, using the same integrated and versatile workspace.

6.1. Sketching a car body

The following example applies all the Spacedesign surfacing potentialities for realizing a car body in a VR workspace. At the very beginning an external simplified model (called “package” by the automotive stylists) is imported in the application as visual reference and constraint (figure 11). Spacedesign introduces for the first time the concept of “3D package”, instead of the traditional 2D template. For the automotive designers the package is just a simplified representation of the car mechanical volumes and the driver. This solution really

helps in the definition of the car shape according the ergonomic/engineering/manufacturing constraints, in a visual and not invasive fashion.

All the surfacing functionalities of Spacedesign are used: extrude for the bonnet, skin for the sides and Coons patch for the roof and the fenders. All the created surfaces can be selected, moved and cancelled, with intuitive gestures. Moreover, during all the working session, the user can navigate the drafted model simply using the navigator axis, and visually check collisions with the reference geometry. Stylists from automotive industry appreciated the simplicity of the application and the immediate feedback of their design intent.

Figure 11. Car body drawing

6.2. Augmented Reality Design

We augmented a physical model of an open car with a virtual roof, for evaluating the overall shape appearance (figure 12). Stylists tried in short time different solutions and discussed them till a final decision. The ultimate model of the cover has been exported in a CAD file ready for the engineering and manufacturing evaluations.

Figure 12. AR car roof drawing

Spacedesign

ARCADE

Preview

Wrinkles

6.3. Augmented Piping

Automotive industry is looking for a solution for designing cabling disposal in still-to be industrialized cars. Established method is to route real pipes inside a physical model, and then reverse engineering the real geometry. An augmented Workspace in Spacedesign has been tested with success in VR for early evaluation, and in AR for optimizations or modifications (figure 13).

Figure 13. An augmented car engine

6.4. Augmented Rapid Prototype

Current rapid prototype techniques do not offer an acceptable level of aesthetic appearance for final evaluations and the creation process is time consuming. We applied Spacedesign to augment some RP pieces built with stereo lithography (which appear pale yellow) with additional textures, colors, and annotations. The user wears the AR glasses and can manipulate the augmented RP for aesthetic estimation (figure 15). Textures and colours can be simply attached to the model just loading them into an array of spheres over the palette and then clicking them with the first button (figure 14).

Figure 14. 3D menu for aesthetic evaluation (left) and the augmented Mock-up (right)

Figure 15. Aesthetic evaluation of a Rapid Prototype

7. Conclusion and Future Work

Spacedesign has been tested from experienced industrial designers mainly from the automotive industry. They appreciate the simplicity of this innovative system because no mathematics of surface are required, which allows short training time. Compared to former CAD programs Spacedesign provides 3D visualization and navigation, real-time editing and intuitive interaction. While in former times their duty was only to produce drawings, with this approach stylists can be active part in the developing process and can better drive their intention along the whole process that leads to the final product.

On the other hand industrial counterparts appreciate this application because of the tight integration from the first creative design to the final reliable model without information loss due to the re-engineering process. In fact great appreciation has been shown for the combination of AR and VR, which leads to a very effective integrated approach.

Nevertheless, many issues should still to be overcome yet. In particular the up to date functionalities are not sufficient to fully design a real car body, which is the main goal of the ongoing Research. Editing of the surfaces is still an issue in VR and new paradigms are necessary for a precise refinement. According to us great advantages in the future can be obtained by means of enhanced virtual constraints and more editing functionalities, which are closer to the stylist’s way of thinking and working.

Also the user interface can be greatly improved via better visualization (using real-time ray-tracing or bump and environment mapping), voice and gesture recognition, context-driven commands and more intelligence in capturing the user's intention. These aspects represent the driving force for our future work.

Virtual Pipe

Acknowledgement

The presented work is part of a European Project in collaboration with Giugiaro Italdesign and Elasis centro Ricerche Fiat. We would like also to thank Prof. J.L. Encarnação for making this work possible, Dr. D. Schmalstieg (Technical University Wien) and Dr. M. Encarnação (Fraunhofer-CRCG Providence, RI) for the Studierstube library.

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