Conceptual design: an operational prescription for a computer support system

in Banissi, E., Sarfraz, M. & Dejdumrong, N. (eds.), Computer Graphics, Imaging and Visualization: New Advances, IEEE & Computer Society, 513521. 4th CGIV07 International conference, Bangkok, August 15-17, 2007.

Conceptual Design: An Operational Prescription for a Computer Support System Oren Shapir, Gabriela Goldschmidt and Abraham Yezioro Faculty of Architecture and Town Planning. Technion - Israel Institute of Technology {[email protected], [email protected], [email protected]} Abstract A prescription for a computer based support system for conceptual design is presented. The necessary components needed are listed, and their implementation in a complete system is shown. Combining the components with the right balance among them is the key to a successful transition of today's conceptual design phase, using pencil and paper, to a computer based system. This work presents ConceptUdraft, a computer system built using this prescription. It allows the creative freedom of freehand 2D and 3D sketching the designer habitually relies on, assists that creative process and elevates it to a higher degree of visualization and interaction. The system developed may contribute to the quality of design and the speed with which conceptual design matures into a feasible new object.

1. Introduction Fast development of Computer Aided Design (CAD) systems for the last 40 years and the huge demand for better products with a shorter time to market, made the design process almost totally computer dependent. Bearing in mind that the first stages of the design process, which incorporate a collection of background material, analysis and production of preliminary sketches of ideas - are most important and have the greatest impact on the final product, we should have had many computer systems by now that support the conceptual stages of design - Computer Aided Conceptual Design (CACD) systems. Surprisingly enough, we do not. Today we still do not have a comprehensive system that allows a designer to start using it as soon as a new design task is launched. Major initial tasks include incorporating data and information collected before and during the conceptual design process and sketching ideas in 2D and 3D, which are combined into one or more spatial representations of the object being designed. The object could be of any type and scale, be it a chair, a car or even a house. A support system should assist the designer throughout the conceptual design process using existing databases of information relevant to the project at hand. Conventional CAD and 3D design systems are widespread these days. Some of these systems are marketed as supporting the conceptual design phase, but

in reality they are intended to assist the designer in the detailed and accurate stages of the design process and in the presentation and production of the final object. They are not effective in supporting the first stages of analysis and conceptual design [1, 2]. Although a lot of work has been done over the years towards creating CACD systems, most of the research in this area focused on one aspect of the problem (e.g., two handed input, converting a 2D sketch to 3D, etc. [3, 4, 5] or on one feature (shape recognition, gesture based manipulation etc. [6] that should be incorporated into such a system. The IDEATE research project described in Stuyver and Hennessey [7], and Ullman [8] who described how a modern design environment should function in the year 2010, are welcome exceptions. Analyzing conceptual design as an activity performed using pencil and paper and translating this manual operation into a sophisticated CACD system without crippling the design process on the way, is the path we took in order to create our prescription of a CACD system. ConceptUdraft, a CACD system developed using the complete prescription (see acknowledgements), allows the designer to work freely and uninterruptedly with the system. The designer can start using the system from the moment the task is initiated, during background material collection and through the entire conceptual design phase. At present the system mimics the look and feel of a physical work environment of a designer and the manual tools used in the design process, due to the lack of available comprehensive alternative computer based tools in the market. Future development will allow the system to offer advice to the designer, create 2D and 3D representations of the design collaboratively, and support seamless integration into CAD/CAM systems for team collaboration and manufacturing.

2. The search for prescription components The search for the right prescription components must start with an investigation of the way conceptual design takes place today. Only by understanding why conceptual design is being carried out the way it does, can we make sure we will not miss vital components in our prescription of a CACD system.

2.1. The conceptual design process – the primacy of sketching The conceptual design process starts as soon as the designer receives the design task. At that time he or she starts collecting information about the problem at hand relevant codes and regulations, ergonomics data, social and economic information, technical data, precedents, and so on. Soon thereafter or even in parallel to data collection, most designers start sketching on paper, using a pen or a pencil. Sketch creation is an integral part of the conceptual design stage and most designers adopt this method as their main mode of thinking [9, 10, 11]. The reasons for that rest with the nature of sketching which allows for fast and rule-free scribbling as well as manipulation of the sheet of paper on which one works by rotating, folding, flipping or cutting it in the process of designing. These possibilities are believed to support creativity [12]. Cognitively speaking, there are more reasons for sketching during the conceptual design stage: generating, clarifying and testing new ideas; enhancing imagination and perception [13]; predicting the consequences of manipulations done on a representation and thus enhancing the abilities of the mind to imagine and evaluate candidate designs [14]; capturing ideas and clarifying the design problem [15]; allowing a free flow of thoughts, and tolerating vagueness which prevents fixation [16]. All this is achieved while only a low cognitive load is imposed on the designer, while expanding his or her capacity to use short-term memory [17]. This means that the lower the amount of cognitive resources (perceptual, memory and sensor-motor) that must be invested, the better for the design process: the designer will concentrate most of his efforts on the design itself, rather than system requirements that must be dealt with. However, the single most important aspect of a design process using sketching at the conceptual phase is an uninterrupted dialog between the designer and him or herself and between the designer and the object that is being designed [18]. Such an ongoing dialog includes checking and feedback - from an image in the mind to an image on paper and vice versa, through an inspection of the sketch and the reading of new information off it [19]. This method of dialog through sketching requires minimal cognitive resources because of its speed and the lack of need for accuracy or completion of sketches. This allows the designer to focus on the design problem rather than on technicalities of the representational system. During the design process the designer is not limited to the use of only one type of representation, namely sketches. Other types of representation can serve as concept triggers, references, or background for sketches. The most common types of representation used beside self-generated sketches are texts, photographs, drawings (all types of maps, floor plans, perspective drawings etc.) and 3D objects. Although these representations can be found in many a place (books, journals, internet, picture albums, etc.), most of the time the designer uses some

kind of photocopying device to transfer them to a sheet of paper. The goal is to create handy 2D background material that may be overlaid with a semi transparent sheet of sketching paper. Using 'imported' representations as background templates for sketches accelerates the process and allows for an examination of alternatives without the need for re-sketching from scratch each time. Incorporating underlying images is possible only by using semitransparent sheets of paper, which creates a distinction between layers of paper (a little washed out) containing different versions of a sketch. Stacking several semi-transparent sheets of paper is possible, thus allowing fast and effortless action.

2.2. Physical characteristics of the conceptual design process The design process, which is embedded in an action/reaction type of work, includes the creation of sketches; visual feedback from those sketches; and the processing of this feedback in the mind, which in turn generates new (reverse) feedback that is channeled back into the process of designing. The use of paper and pencil enables the fast creation of a sketch and instant visual feedback from it; continuous cycles of this nature enable smooth progress. There is a direct visual connection between the movement of the drawing tool on the sheet of paper and perceived feedback from the same sheet of paper: the designer does not have to move his or her head and hands to seek visual feedback elsewhere. The designer manages to achieve direct manipulation and feedback by assigning the "work" to two hands, allowing one (the dominant hand) to be in charge of the actual design creation while the eyes are focused on the drawing surface. The other hand (the nondominant) assists the creation without interrupting it. Such division of the work load is based on three rules: a. The scope of action is different – the dominant hand operates relative to the space where the nondominant hand operates [20]. b. Both hands operate at different scales and at different frequencies. (The non-dominant hand operates at a larger scale and at a lower frequency than the dominant hand) [21]. c. The non-dominant hand operates ahead of the dominant hand [21]. For example, during sketching, the non-dominant hand enables the designer to position and rotate the sheet of paper in a way that helps the dominant hand operate better and faster [22].

3. Specifying components for a wellbalanced prescription Specifying each component in the prescription for creating a computer system for conceptual design must be dealt with using utmost caution, lest one of the most negative aspects of such a prescription - cognitive load -

will dominate it and render the system unsuitable for its purpose by crippling the design process. When using a computer system cognitive resources must be devoted to system requirements: series of commands that translate the user's intentions into a 'language' comprehensible to the system [23]. This translation which is in fact a secondary, unnatural task, takes too long and results in less attention to the primary task: designing. Therefore the first and most important principle to be embedded in a CACD system prescription should be: (i) Do NOT disturb the design process by cutting the line of thought via the imposition of performance of system-oriented tasks. The design process should progress at its own inherent pace, without disruptions, delays or accelerations due to system operation requirements [24].

3.1. Physical interface Lack of adequate direct physical feedback from the design tool to the designer is one of the characteristics of today's computer based design systems. In manual work with pen and paper, the mere contact of the nondominant hand with the sheet of paper allows for movement and rotation without burdening the designer's cognitive resources and with no obligation to shift the center of attention from the design itself to peripheral zones. Also, the direct creation of the manual sketch allows for the essential dialog between the designer and the evolving sketch. Another characteristic is the lack of two-handed interfaces for computer systems. Even where such an interface exists, it is not congruent with the natural and instinctive way of using both hands (see section 2.2). There are three main reasons for using two hands while designing with a computer system: (a) parallel work shortening the time each hand works to finish a task; (b) distributed tasks enable each hand to travel less (moving the cursor on the screen); and (c) dependent relationship between the two hands - one hand helps the other, which reduces the overall work load. Much research was carried out on the subject of two-handed interface in 2D and 3D design systems [20, 22, 25, 26]. All researchers came to the conclusion that a computer system would benefit from a two handed interface if it could be used intuitively and in a manner similar to the way we use two hands in other tasks in daily life. Clearly, achieving fluency requires practice and cannot be expected to be instantaneous. Following that, two new components to the prescription were added: (ii) A physical interface which allows for direct manipulation and feedback from the virtual interface. A CACD system based on such interface reduces the amount of attention needed to perceive the current state of the design and allows the uninterrupted and direct generation and manipulation of sketches by the designer. (iii) A two handed interface based on a hierarchy by dominance of the hands, mutual dependability and

different scales and frequencies of operation, carried out in an intuitive, natural manner.

3.2 Virtual interface The virtual user interface in computer systems is responsible for substantial waste of cognitive resources. Today most work screens in design software are divided into several areas: (a) menus - at the top of the screen; (b) information lines - at the bottom of the screen; (c) toolbars - at the left and right sides of the screen; (d) work area - what is left in the middle of the screen. In most 3D design tools, this area is itself divided into a few subparts, dedicated to different viewpoints of the object. According to Kurtenbach et al [27], two main problems arise from the screen division: (a) the actual work area left to the designer is very small, especially when compared with the area taken up by menus and toolbars. This forces the user to pan and zoom at a very high frequency, which disturbs the continuity and uninterrupted use of feedback during the design process; (b) the cursor must be repeatedly shifted from the work area to menus and toolbars, thus distracting the designer and interrupting the design process. The problem of divided attention between the design area and support areas (menus, toolbars etc.) has a negative influence on the quality of interaction between the designer and the computer system [28]. In most CAD systems, the user interface stands between the user and representations of the designed entity. The user must conform to the requirements of the interface by using those menus, toolbars, etc. in the correct sequence to perform manipulations on models or images, as opposed to manual sketching in which manipulations are done directly on the representation of the designed entity, with no filtering between the two. The last two components must therefore: (iv) CACD systems must support the direct manipulation of models or images, be they sketches or any other type of representation used in the process of designing. They should work alongside the designer and the sketch, and not stand between them. (v) The user interface must have minimal to no impact on the designer's working area, avoiding the use of menus, toolbars etc. in the system, thus allowing the designer to stay focused on the design itself.

4. The complete prescription The complete prescription is embedded in the ConceptUdraft system. ConceptUdraft integrates almost all of the components mentioned above into one complete operational solution for conceptual design support using a computer system. ConceptUdraft allows the free, direct and uninterrupted flow of design activity by a combination of a physical and a virtual interface. The combination allows the direct manipulations of design representations with both fresh and re-visited sketching sheets as well as different types of other images (photos, texts, 3D objects etc.) imported into it.

ConceptUdraft is based on a vector system that allows for further inclusion of virtual tools to enhance the design process, such as information based support systems and auto-generated 3D model representations out of 2D sketches. Figure 1 is a diagram of the complete prescription. In the lower part, the bottom double-box of each vertical string compares the features of ConceptUdraft with currently available state of the art commercial or prototype (research) systems intended for the conceptual phase of the design process. The rest of section 4 is a detailed presentation and explanation of the major features of ConceptUdraft. At this development stage, the prescription tries to map the actual manual way of work at the conceptual design stage onto a computerized environment, since this is the desired way of keeping in track of the design ideas development. Future development will allow for a more comprehensive integration with different computerized resources, so they can be embedded more effectively on the design process (a few temporary alternative routes had to be taken in order to overcome hardware, time and resource shortcomes: some extended assistance modules and complex 2D to 3D conversions will be executed in the future).

to input the sketches, manipulate the data in the system and get direct feedback from it. Such hardware interface is not commercially available at present, but overlaying two products can give the desired. The use of a Wacom Cintiq 21.3" LCD digitizer overlaid by a touch screen enables the designer to create and manipulate a sketch using a digital pen with the dominant hand, while the touch screen allows for the non dominant hand to manipulate the working area, assisting the dominant hand. Such a prototype device (using a tablet pc overlaid by a touch screen) was shown to work satisfactorily [29]. Due to the lack of a commercially available device ConceptUdraft was built around a digitizer tablet that allows for simultaneous two-handed input: the dominant hand uses a digital movement-pressure-angle-inclination sensitive pen and the non-dominant hand uses a movement-rotation sensitive mouse. Both work on the same tablet surface - a Wacom Intuos II A3. A partial solution to the lack of direct visual contact with the design tool (the designer looks at the computer screen where the sketch is displayed whereas the design tool is on the tablet) is provided by a virtual 3D model of the design tool (pen, pencil etc.). The tool is represented on the virtual interface (screen), thus allowing the designer to keep looking at the sketch and getting visual feedback from the virtual design tool (Figure 2).

4.1 Physical interface

Prescription

The designer who uses the system should have a two handed direct manipulation hardware interface in order

Figure 1: The complete prescription - diagram.

4.2 Virtual interface The virtual interface is divided into two main parts: (a) Project management module (Figure 3) consists of a filing system and a list of projects, summary information and a worktable pictogram for each project. (b) Design module (see Figure 4) - the virtual worktable on which the process of research and design through sketching and other data integration takes place. 4.2.1. Project management. The project management module allows the designer to manage projects under folders. Each project is a new worktable consisting of all sketch sheets and other data types. The module is designed for simple and direct use - no menus or sub-menus. Information input is done using a keyboard, handwriting recognition or a virtual keyboard. (handwriting recognition is yet to be implemented in ConceptUdraft). 4.2.2. Design module. The design module consists of one screen. The work area is shaped after a real designer's work environment, as follows: The semi-transparent sheet of paper (B in Figure 4) is the main object in the work area. It contains sketches as well as other optional representations such as pictures, texts and 3D objects, if the designer brings them in. Any number of sheets of paper may be placed on the work surface at any given time, thus allowing for tracing over other sketches or over pictures or 3D objects on other sheets of paper whenever the need arises. Sheets of paper are controlled by the non-dominant hand which moves, rotates, flips and folds them (flipping and folding are yet to be implemented in ConceptUdraft). Each sheet has a title bar (Figure 5) that allows to: remove it from the work area by pressing a button (A); throw it into the garbage bin (B); change its title (C); stamp it with the time of its creation (D) or its last revision (E); change the opacity level (F) and the background color (G); fixate the sheet to the work surface to prevent its movement (H); and a 'link sheets' facility used when sheets are to move/rotate together (I). Sketching on sheets of paper is done using the dominant hand, which holds the digital pen. Lines created in freehand sketching have the properties and looks typical of the tool used to create them. For example, the marker generates soft lines that get thicker and more opaque as the user presses harder on the digitizer surface with the digital pen. A selection of drawing tools (pen, pencil, markers etc.) permits a faithful simulation of manual sketching on regular paper using different tools (see Figure 6). Similar to sketch lines, entities such as photos, text and 3D objects can be placed freely on the sketch sheet, allowing the designer to use them as background for sketching, extra sources of additional information, or as any other resource (see Figure 7). Managing and editing objects (be they sketch lines or other representations) involves two steps: (a) Selecting an object - sketch lines, photos, texts or 3D objects. There are two selection options: 1) when one line is picked, a group of interlinked lines is

automatically selected. Interlinked lines are those lines produced by the pen without lifting it off the digitizer; 2) a group of lines may be encircled by drawing a line around them while pressing a button on the digital pen: this interlinks them for the purpose of editing. Selecting photos, texts and 3D objects is done the same way.

Figure 2: A 3D virtual design tool (pen) - as feedback indicating the physical tool's location and inclination.

Figure 3: Project management module screen Available folders (A); project in a selected folder (B); extended information on the selected project (C); a pictogram representing the work (D); folder manipulation (E); project manipulation (F); entry into the design module and exit from the system (G).

Figure 4: Design module screen - Background (A); sheet(s) of paper (B); the last sheets of paper, removed from the work area - pictograms at the top (C); extra module tabs (D); undo and exit buttons (F and E).

Figure 5: Sketch sheet title bar.

Figure 6: Different sketch lines.

Figure 7: (left to right) Photo editing; sketch lines; text; 3D object.

Figure 8: Pie menu.

Figure 9: The tool chest: a) pen; b) pencil; c) thin marker; d) wide transparent marker; e) text tool; f) add a new sketch sheet; g) color palette; h) palette of last colors used.

(b) Editing - Using hot spots on the corners of selected objects, the designer can arrange and edit the selected objects by dragging hot spot corners and using simple gestures (hot spots and gesture recognition are yet to be implemented in the system). Another option is the translucent pie menu that pops up on the selected object (see Figure 8). Using pie menus instead of regular pulldown/pop-up menus shortens the distance the pen must travel in order to select commands, thus allowing the designer faster selection. An experienced user has to remember only the pie-slot position of each commandicon. This is made easy by the circular arrangement of the icons. Pie menu icon arrangement is identical for each object type to allow for easy, almost automatic, use of pie menus. Pie menus appear on request, and as such they represent part of the design process. They are the tool that permits manipulations of the sketch, as done in a manual sketching process where the designer extends his hand to pick the eraser, or another similar task. The advantage of the pie menu over the “traditional” GUI Windows based menus on the top, is that they appear on request, semi-transparently over the sketch to allow for direct manipulation and keeping the designer's focus on the sketch itself and not on the tools. Two-handed input in this system allows the dominant hand to sketch without interruption while the designer focuses on the design and not on moving, rotating, flipping or folding the sheet of paper. Furthermore, in this system the non-dominant hand controls a toolchest that contains different drawing tools and sheets of paper (Figure 9). When the designer wants to change a drawing tool, the non-dominant hand moves the toolchest to where it is wanted on the sheet of paper – again, allowing for less interruption of the sketching process and less movement of the eye away from the sketch. There are more tools controlled by the non-dominant hand that assist the dominant hand: a) scale ruler with different scales for the purpose of measuring and drawing straight lines (see Figure 10); b) background grids (see Figure 11); c) eraser that acts like a regular eraser by turning the digital pen upside down and erasing (see Figure 12).

Figure 10: Scale ruler.

Figure 11: Grids - options are selected from the pie menu.

Figure 12: Stages of erasing sketch lines with the eraser: a) flipping the digital pen to the eraser end; b) erasing while pressing on the digitizer button; c) lifting the digital pen from the digitizer - sketch lines are erased.

Figure 13: Module tabs: a) information; b) reference material; c) sketch notebook; d) trash bin. 4.2.2.1. Extra Module Tabs. During the design process hundreds and even thousands of sheets of paper are created and archived. In order to manage this vast amount of information and accommodate it as well as information imported from other sources, a new visual archiving metaphor which allows for a natural and fluent use of the resources is required. Conforming to the folder/files metaphor of the operating system UI would not allow for a fast retrieval of the visual and non visual

information needed for the design and would shift the designer's attention from the images he or she needs to a list of folder/files to be memorized. In order to allow the designer to use the desired information as fast as possible the support information is divided into six separate sections that reside on the desktop as small tabs, accessed by tapping the appropriate module tab on the left side of the work area. This opens it over half of the current work area (see D in Figure 4). The metaphor corresponding to manual sketching is desk drawers, where normally the designer archives the background material. So while in the “actual” physical environment, the designer draws the material from drawers, in the virtual environment this material is drawn from the tabs. In its present version, ConceptUdraft has four implemented module tabs (see Figure 13): a) Information - general information and specifications regarding the object being designed. It is normally created by the designer himself and allows him to keep track of the design description, client related information, etc; b) Reference material - every piece of background material (photos, maps, texts, 3D objects etc.) that the designer has collected before and during the design process; c) Sketches - a sketch notebook that contains pictograms of all sketch sheets ever created in the project. The notebook facilitates finding older sketches with the help of a search engine, yet to be implemented; d) Trash bin - contains all the sketch sheets thrown into the trash bin for possible retrieval later, or reference material that at some point the designer may dispose of. Two additional modules are to be implemented in later versions of the system (not yet implemented and not shown in Figure 13), namely: e) Index - a general index of sketch sheets of all the projects in the system which allows the designer to access material from his other projects. The index also allows for an accurate material search by keywords, type, dates etc. f) Interactive WWW search engine that automatically fetches visual and non visual 2D and 3D information relevant to the project at hand, by using keywords taken from the project information tab and keywords which were entered as noted on the sketch sheets themselves. This tab also allows for manual and semi-automatic information search using conventional search engines. To use the information and objects in the reference support module, the designer has only to drag it to a sheet of paper for further processing. Information (text, pictures, 3D objects, etc.) is not erased by dragging it from place to place; it remains stored for future use until deliberately deleted by the designer. The retrieval of deleted or archived sketch sheets is realized by a simple point-and-click on the corresponding pictogram.

5. Using the completed prescription The process of learning to use this new tool is expected to be as simple as it is to draw with a pen on paper, literally. No special skills are required from the user other than using his two hands and a pen. The only techniques he/she needs to learn are the following: a) executing the interface; b) browsing the list of projects and choosing which one to activate; c) creating sketches; d) using the support material; and e) operating the tablet pen. At the present stage of development of ConceptUdraft, the expectations from the systems are largely fulfilled.

6. Summary Only by investigating the actual conceptual design process and its reliance on sketching, using paper and pencil, and by understanding the fundamental advantages of this manual design strategy, can we start thinking about ways in which a computer system for conceptual design should function. A good understanding of the process is vital in order to focus on proper ways in which a computer system might enhance the design process. Uninterrupted freehand sketching is fundamental to conceptual design processes. It enables direct manipulation of design images and feedback from external representations, thus supporting the dialog between the designer and the designed entity. Furthermore, using two hands during the conceptual design phase helps maintain a continuous dialog by allowing the dominant hand to focus on sketching while the non-dominant hand assists in maneuvering the work area and various design tools. Using semi-transparent sheets of sketch paper allows for the incorporation of other types of representation such as photos, maps, texts, perspective views and other sketches - as background for sketching or faster evaluation of alternatives. A comprehensive computer system is proposed for the conceptual design stage: ConceptUdraft. The ConceptUdraft system, shaped according to the prescription presented, avoids the traditional user interface, found in practically every CAD system, which consumes too much of the designer's precious cognitive resources by forcing a rigid and linear workflow to suit the system's 'understanding'. The proposed system has a physical interface that supports direct manipulation and two handed design, whereas most CAD systems conform to the use of a single handed interface - a mouse - or at most the use of the keyboard as a second hand support. ConceptUdraft shows that the prescription for a computerized conceptual design system, as presented in this paper can be achieved. Also, instead of suffering from the transition to a computerized system, the process rewards its user in many ways. These include better incorporation and management of sketches and other representations; faster retrieval of alternatives and inspection of past sketches; and an integrated platform for design assistance modules that work in parallel to the

designer's progress rather than after the design has been completed. The paper shows that the traditional computer interface is not suitable for a conceptual design support system. CACD systems must allow the designer to focus on the design itself, on the sheet of paper, with no distraction caused by the need to attend to system requirements. ConceptUdraft is a working prototype CACD system that allows the designer to make the move from traditional pen and paper to a computer system without constraining the design process and with the added benefits of design support modules. As a platform for real time assistance components, the system can accept new modules for real time retrieval of design information from the internet or other information databases, evaluation modules (ergonomics, structural analysis, building codes, energy consumption, etc.) and 3D extrapolation modules, to allow for automatic 3D sketch creation from 2D elevations.

Acknowledgements This paper is based on the first author's Master's thesis at the Technion (including the development of ConceptUdraft) under the supervision of the second and third authors. The research involved and the writing of the paper were partially supported by grants to the latter authors from the fund for the promotion of research at the Technion, hereby gratefully acknowledged.

References [1]

[2]

[3]

[4]

[5]

[6]

[7]

S.N. Pollalis, Towards the Automation of Conceptual Design, in A. Tzonis and I. White (Eds.) Automation Based Creative Design – Research and Perspective, Elsevier Science B.V. 1994. H. Lipson, Man-Machine Interface for 3D CAD Based on Freehand Sketching, Research Thesis, Israel Institute of Technology, Haifa, 1998. Takeo Igarashi, Satoshi Matsuoka, Hidehiko Tanaka, "Teddy: A Sketching Interface for 3D Freeform Design" ACM SIGGRAPH'99, Los Angeles, 1999, 409-416. Shigeru Owada, Frank Nielsen, Kazuo Nakazawa, Takeo Igarashi, "A Sketching Interface for Modeling the Internal Structures of 3D Shapes", Proceedings of 3rd International Symposium on Smart Graphics, Lecture Notes in Computer Science, Springer, Heidelberg, Germany, July 2-4, 2003, 49-57. Takeo Igarashi, John F. Hughes, "A Suggestive Interface for 3D Drawing ", 14th Annual Symposium on User Interface Software and Technology, ACM UIST'01, Orlando, Florida, November 11-14, 2001, 173-181. Takeo Igarashi, "Freeform User Interfaces for Graphical Computing", Proceedings of 3rd International Symposium on Smart Graphics, Lecture Notes in Computer Science, Springer, Heidelberg, Germany, July 2-4, 2003, 39-48. R. Stuyver and J.M. Hennessey, A Support Tool For The Conceptual Phase Of Design, People and Computers X, Edited by: Kirby, MAR, Dix, A.J. and Finlay, Cambridge, J.E.,Cambridge University Press, 1995, pp. 235-245.

[8]

[9]

[10] [11] [12]

[13] [14]

[15]

[16] [17]

[18] [19]

D. Ullman, The Foundations of the Modern Design Environment:- An Imaginary Retrospective, in N. Cross, K. Dorst and N. Roozenburg, (Eds): 1992, Research in design thinking, Proceedings of a workshop meeting held at the Faculty of Industrial Design Engineering, Delft University of Technology, The Netherlands, 1992, pp. 61-73. A. Pipes, Drawing for 3-Dimensional Design: Concepts, Illustrations, Presentation, London, Thames and Hudson, 1990. B. Lawson, Design in Mind, Oxford, UK, Butterworth Architecture, 1994. N. Cross, Natural intelligence in design, Design Studies, 20(1), 1999, 25-39. G. Goldschmidt, Read-Write Acts of Drawing, or - The Economy of Treasure Hunting, TRACY Contemporary drawing issues, 2002, http://www.lboro.ac.uk/departments/ac/tracey/somag/gab i.html. N. Negroponte, On Being Creative with Computer Aided Design, Information Processing, 77, 1977, 695-704. J. Fish and S. Scrivener, Amplifying the Mind’s Eye: Sketching and Visual Cognition, LEONARDO 23(1), 1990, 117-126. P.A. Rodgers, G. Green and A. McGown, Using Concept Sketches to Track Design Progress, Design Studies 21(5), 2000, 451-464. M. Puttre, Gearing up for Conceptual Design, Mechanical Engineering, March 93', 1993, 46-50. D.L. Jenkins and R.R. Martin, Applying constraints to enforce users' intentions in free-hand 2-D sketches, Intelligent Systems Engineering autumn, 1992, 31-49. D.A. Schön, The Reflective Practitioner, New York, Basic Books, 1983. G. Goldschmidt, The Dialectics of Sketching, Creativity Research Journal 4(2), 1991, 123-143.

[20] K. Hinckley, R. Pausch, D. Proffitt, J. Patten and N. Kassell, Cooperative Bimanual Action, ACM CHI'97 Conference on Human Factors in Computing Systems, 1997, 27-34. [21] Y. Guiard, Asymmetric Division of Labor in Human Skilled Bimanual Action: The Kinematic Chain as a Model, Journal of Motor Behavior 19(4), 1987, 486-517. [22] R.C. Zeleznik and A.S. Forsberg, Two Pointer Input For 3D Interaction, Brown University site of the NSF Science and Technology Center for Computer Graphics and Scientific Visualization, 1997. [23] T. Igarashi, S. Kawachiya, S. Matsuoka and H. Tanaka, In Search for an Ideal Computer-Assisted Drawing System, INTERACT'97 (The Sixth IFIP Conference on Human-Computer Interaction), Sydney, Australia, 14-18 July, 1997, 104-111 [24] M. McCullough, Abstracting Craft – The Practiced Digital Hand, Cambridge, MA, MIT Press, 1998. [25] P. Kabbash, W. Buxton and A. Sellen, Two-Handed Input in a Compound Task Proceedings of CHI ’94, 1994, 417-423. [26] W. Buxton and B.A. Myers, A Study in Two-Handed Input, CHI 86, 1996, 321-326. [27] G. Kurtenbach, G. Fitzmaurice, T. Baudel and W. Buxton, The design of a GUI paradigm based on tablets, two-hands and transparency, Proceedings of CHI ’97, New York, NY, 1997, 35-42. [28] T. Baudel, A Mark-Based Interaction Paradigm for FreeHand Drawing, ACM-SIGGRAPH and SIGCHI, Proc. ACM Symposium on User Interface Software and Technology (UIST), 1994. [29] Y. Ka-Ping, Two-Handed Interaction on a Tablet Display, Proceedings of CHI '04, 2004.