A survey of sketch-based 3-D modeling techniques
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paper_title: In Search for an Ideal Computer-Assisted Drawing System

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Diagram drawing with conventional computer-assisted drawing(CAD) editors often tend to take considerable amount of time despite their seeming ease of use. We analyzed the problems of such systems focusing on the problem of cognitive overload, and observed that 1) the necessity of cognitive planning process in current CAD system causes the problems and that 2) reducing the overload can lead to fundamental improvement in overall drawing efficiency. We have conducted an experiment to verify these observations by comparing a typical drawing system and our prototype drawing system called Interactive Beautification, which combines the ease of freehand drawing and precision of traditional drawing editors by extracting various constraints in input strokes, and generating the desired diagrams automatically. Results show that significant amount of time is spent for cognitive planning process, and reduction of such planning time by Interactive Beautification can significantly improve the efficiency of CAD.
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paper_title: Drawing as a means to design reasoning

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We investigate the functions of drawing in design and how, based on these functions, a computational sketching environment might support design reasoning. Design, like all problem solving activities, involves reasoning— making decisions, expressing ideas, verifying and evaluating proposals, and ultimately, taking action. For designers, drawing is a vehicle for design reasoning, and therefore the spontaneous marks made on paper during sketching form a partial record of the designer’s thinking. Most designers sketch early design ideas with a pencil on paper: sketching is still the quickest and most direct means to produce visual representations of ideas. The ambiguity of free hand sketching allows multiple interpretations and thus stimulates the production of more design alternatives. The linked acts of drawing and looking invite designers to recognize new interpretations of the alternatives they propose. By drawing and looking, designers find visual analogies, remember relevant examples, and discover new shapes based on previously unrecognized geometric configurations in their sketches. 1. Thinking with a pencil Visual representations such as freehand sketches and concept diagrams seem to play a significant role in design problem solving. Design reasoning is accompanied by, and we might say, embedded in, the act of drawing. Sketching on paper and pencil supports ambiguity, imprecision, and incremental formalization of ideas as well as rapid exploration of alternatives.
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paper_title: Sketching with a low-latency electronic ink drawing tablet

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Drawing on paper is an experience which is still unmatched by any input device for drawing into a computer in terms of accuracy, dexterity and general pleasantness of use. This paper describes a paper-like drawing tablet which uses electronic ink as its output medium with stylus-based touchpanel input. The device mimics the experience of drawing in a manner which can be adjusted to approach the feel of different kinds of paper. We discuss further some basic issues which need to be addressed in managing interfacing to such a device, specifically the avoidance of the legacy of mouse-oriented point-and-click interfaces which have influenced GUI design for so long. We see a sketch-based model for interaction, based on free-form curve drawing, as being the way forward but new interaction models are required. The tablet is initially intended to serve as an input-device for cartoon drawing and editing, so the product of any sketching process has to be presented to the rest of the animation data-path in terms of a conventional curve model, here Bezier chains. We discuss models for achieving this without having to resort to legacy curve-editing techniques which have no counterpart in drawing on paper or in the repertoire of the traditional animator. Potential uses of these interaction techniques go well beyond supporting the cartoon drawing application.
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paper_title: Sketching with a low-latency electronic ink drawing tablet

paper_content:

Drawing on paper is an experience which is still unmatched by any input device for drawing into a computer in terms of accuracy, dexterity and general pleasantness of use. This paper describes a paper-like drawing tablet which uses electronic ink as its output medium with stylus-based touchpanel input. The device mimics the experience of drawing in a manner which can be adjusted to approach the feel of different kinds of paper. We discuss further some basic issues which need to be addressed in managing interfacing to such a device, specifically the avoidance of the legacy of mouse-oriented point-and-click interfaces which have influenced GUI design for so long. We see a sketch-based model for interaction, based on free-form curve drawing, as being the way forward but new interaction models are required. The tablet is initially intended to serve as an input-device for cartoon drawing and editing, so the product of any sketching process has to be presented to the rest of the animation data-path in terms of a conventional curve model, here Bezier chains. We discuss models for achieving this without having to resort to legacy curve-editing techniques which have no counterpart in drawing on paper or in the repertoire of the traditional animator. Potential uses of these interaction techniques go well beyond supporting the cartoon drawing application.
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paper_title: Calligraphic Interfaces: Mixed Metaphors for Design

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CAD systems have yet to become usable at the early stages of product ideation, where precise shape definitions and sometimes even design intentions are not fully developed. To overcome these limitations, new approaches, which we call Calligraphic Interfaces, use sketching as the main organizing paradigm. Such applications rely on continuous input modalities rather than discrete interactions characteristic of WIMP interfaces. However, replacing direct manipulation by sketching alone poses very interesting challenges. While the temptation to follow the paper-and-pencil metaphor is great, free-hand sketch recognition remains an elusive goal. Further, using gestures to enter commands and sketches to draw shapes requires users to learn a command set – sketches do not enjoy the self-disclosing characteristics of menus. Moreover, the imprecise nature of interactions presents additional problems that are difficult to address using present-day techniques.
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paper_title: Free-form Sketching with Variational Implicit Surfaces

paper_content:

With the advent of sketch-based methods for shape construction, there’s a new degree of power available in the rapid creation of approximate shapes. Sketch [Zeleznik, 1996] showed how a gesture-based modeler could be used to simplify conventional CSG-like shape creation. Teddy [Igarashi, 1999] extended this to more free-form models, getting much of its power from its "inflation" operation (which converted a simple closed curve in the plane into a 3D shape whose silhouette, from the current point of view, was that curve on the view plane) and from an elegant collection of gestures for attaching additional parts to a shape, cutting a shape, and deforming it. But despite the powerful collection of tools in Teddy, the underlying polygonal representation of shapes intrudes on the results in many places. In this paper, we discuss our preliminary efforts at using variational implicit surfaces [Turk, 2000] as a representation in a free-form modeler. We also discuss the implementation of several operations within this context, and a collection of user-interaction elements that work well together to make modeling interesting hierarchies simple. These include “stroke inflation” via implicit functions, blob-merging, automatic hierarchy construction, and local surface modification via silhouette oversketching. We demonstrate our results by creating several models.
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paper_title: Sketching with a low-latency electronic ink drawing tablet

paper_content:

Drawing on paper is an experience which is still unmatched by any input device for drawing into a computer in terms of accuracy, dexterity and general pleasantness of use. This paper describes a paper-like drawing tablet which uses electronic ink as its output medium with stylus-based touchpanel input. The device mimics the experience of drawing in a manner which can be adjusted to approach the feel of different kinds of paper. We discuss further some basic issues which need to be addressed in managing interfacing to such a device, specifically the avoidance of the legacy of mouse-oriented point-and-click interfaces which have influenced GUI design for so long. We see a sketch-based model for interaction, based on free-form curve drawing, as being the way forward but new interaction models are required. The tablet is initially intended to serve as an input-device for cartoon drawing and editing, so the product of any sketching process has to be presented to the rest of the animation data-path in terms of a conventional curve model, here Bezier chains. We discuss models for achieving this without having to resort to legacy curve-editing techniques which have no counterpart in drawing on paper or in the repertoire of the traditional animator. Potential uses of these interaction techniques go well beyond supporting the cartoon drawing application.
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paper_title: Cascading recognizers for ambiguous calligraphic interaction

paper_content:

Throughout the last decade many approaches have been made to the problem of developing CAD systems that are usable in the early stages of product ideation. Although most of these approaches rely on some kind of drawing paradigm and on the paper-and-pencil metaphor, only a few of them deal with the ambiguity that is inherent to natural languages in general and to sketching in particular. Also the paper-and-pencil metaphor has not in most cases been fully accomplished, since many gesture-based interfaces resort to secondary buttons and modifier keys in order to make command strokes easier to differentiate from their geometry instantiating counterparts. In this paper we describe the architecture of GIDeS++, a sketch-based 3D modeling system that approaches these problems in three different ways: by dealing with ambiguity and exploring it to the user's benefit; by reducing the command set and thus minimizing the cognitive load on the user; and by cascading different types of gesture recognizers, which allows interaction to resort only to the button located on the tip of an electronic stylus.
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paper_title: A suggestive interface for 3D drawing

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This paper introduces a new type of interface for 3D drawings that improves the usability of gestural interfaces and augments typical command-based modeling systems. In our suggestive interface, the user gives hints about a desired operation to the system by highlighting related geometric components in the scene. The system then infers possible operations based on the hints and presents the results of these operations as small thumbnails. The user completes the editing operation simply by clicking on the desired thumbnail. The hinting mechanism lets the user specify geometric relations among graphical components in the scene, and the multiple thumbnail suggestions make it possible to define many operations with relatively few distinct hint patterns. The suggestive interface system is implemented as a set of suggestion engines working in parallel, and is easily extended by adding customized engines. Our prototype 3D drawing system, Chateau, shows that a suggestive interface can effectively support construction of various 3D drawings.
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paper_title: Correlation-based reconstruction of a 3D object from a single freehand sketch

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We propose a new approach for reconstructing a three-dimensional object from a single two-dimensional freehand line drawing depicting it. A sketch is essentially a noisy projection of a 3D object onto an arbitrary 2D plane. Reconstruction is the inverse projection of the sketched geometry from two dimensions back into three dimensions. While humans can do this reverse-projection remarkably easily and almost without being aware of it, this process is mathematically indeterminate and is very difficult to emulate computationally. Here we propose that the ability of humans to perceive a previously unseen 3D object from a single sketch is based on simple 2D-3D geometrical correlations that are learned from visual experience. We demonstrate how a simple correlation system that is exposed to many object-sketch pairs eventually learns to perform the inverse projection successfully for unseen objects. Conversely, we show how the same correlation data can be used to gauge the understandability of synthetically generated projections of given 3D objects. Using these principles we demonstrate for the first time a completely automatic conversion of a single freehand sketch into a physical solid object. These results have implications for bidirectional human-computer communication of 3D graphic concepts, and might also shed light on the human visual system.
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paper_title: Gestalt Isomorphism and the Primacy of Subjective Conscious Experience: A Gestalt Bubble Model

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A serious crisis is identified in theories of neurocomputation, marked by a persistent disparity between the phenomenological or experiential account of visual perception and the neurophysiological level of description of the visual system. In particular, conventional concepts of neural processing offer no explanation for the holistic global aspects of perception identified by Gestalt theory. The problem is paradigmatic and can be traced to contemporary concepts of the functional role of the neural cell, known as the Neuron Doctrine. In the absence of an alternative neurophysiologically plausible model, I propose a perceptual modeling approach, to model the percept as experienced subjectively, rather than modeling the objective neurophysiological state of the visual system that supposedly subserves that experience. A Gestalt Bubble model is presented to demonstrate how the elusive Gestalt principles of emergence, reification, and invariance can be expressed in a quantitative model of the subjective experience of visual consciousness. That model in turn reveals a unique computational strategy underlying visual processing, which is unlike any algorithm devised by man, and certainly unlike the atomistic feed-forward model of neurocomputation offered by the Neuron Doctrine paradigm. The perceptual modeling approach reveals the primary function of perception as that of generating a fully spatial virtual-reality replica of the external world in an internal representation. The common objections to this picture-in-the-head concept of perceptual representation are shown to be ill founded.
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paper_title: On seeing things

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The importance of effective task representations in the design of programs intended to exhibit sophisticated behaviour manifests itself in the area of Picture Interpretation as the so-called 'Linguistic Approach'. A brief survey of Pattern Description Languages leads up to an analysis of a simple letter recognition task from which it is argued that at least two types of description of the pattern must be utilised if any significant pattern generalisation is to be achieved, and in general that all picture interpretation tasks involve descriptions in two domains. Further support for this viewpoint is provided by a characterization of the problem of interpreting line diagrams as pictures of three dimensional sceness, in which the form of these decriptions and of their interrelation by an algorithm is described in detail. The paper concludes by relating these ideas to the distinction between syntax and semantics, and the concept of denotation.
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paper_title: Impossible Objects as Nonsense Sentences

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To every 3-dimensional scene there correspond as many 2-dimensional pictures as there are possible vantage points for the camera. It is, however, possible to construct pictures for which there is no corresponding scene containing physically-realizable objects. Pictures of such 'impossible objects' can be useful in giving insight into the constraints or grammatical rules associated with the 'language' of pictures, just as nonsense sentences can be useful in illustrating the rules of other languages. Impossible objects have been used by psychologists (Penrose and Penrose 1958) to create visual illusions which successfully challenge the ability of our perceptual systems to synthesize a 3-dimensional world from 2-dimensional information. The incompatibilities among the various portions of pictures of these objects are a novel way of testing our picture analysis procedures. The purpose of this paper is to demonstrate some possible decision procedures and to test them on pictures of both possible and impossible objects.
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paper_title: Sketching a virtual environment: modeling using line-drawing interpretation

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Here we demonstrate the direct input to computer of a handdrawn perspective sketch to create a virtual environment. We either start with a photograph of a real environment or an existing VRML model, and then use a mouse or pen pad to sketch line drawings onto the scene. Visual clues and constraints from the existing background and line drawing, as well as heuristics for form recognition are used to build a 3D optimization problem. We use a multiple objective genetic algorithm to find a viable solution to the problem, and VRML output is generated, either for re-entry to the system or use in another system. Our software is currently available compiled for either a PC running Windows 98/NT or an SGI machine running IRIX 6.x.
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paper_title: Creating solid models from single 2D sketches

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We describe a method of constructing a B-rep solid model from a single hidden-line removed sketch view of a 3D object. The main steps of our approach are as follows. The sketch is first tidied in 2D (to remove digitisation errors). Line labelling is used to deduce the initial topology of the object and to locate hidden faces. Constraints are then produced from the line labelling and features in the drawing (such as probable symmetry) involving the unknown face coefficients and point depths. A least squares solution is found to the linear system and any grossly incompatible equations are rejected. Vertices are recalculated as the intersections of the faces to ensure we have a reconstructible solid. Any incomplete faces are then completed as far as possible from neighbouring faces, producing a solid model from the initial sketch, if successful. The current software works for polyhedral objects with trihedral vertices. CR Descriptors: I.3.5 [Computer Graphics]: Computational Geometry and Object Modelling Geometric algorithms, languages and systems; I.2.10 [Artificial Intelligence]: Vision and Scene Understanding Perceptual reasoning; I.3.6 [Computer Graphics]: Methodology and Techniques Interaction techniques; J.6 [Computer Applications]: CAE CAD.
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paper_title: Can Machines Interpret Line Drawings?

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Engineering design would be easier if a computer could interpret initial concept drawings. We outline an approach for automated interpretation of line drawings of polyhedra, and summarise what is already possible, what developments can be expected in the near future, and which areas remain problematic. We illustrate this with particular reference to our own system, RIBALD, summarising the published state of the art, and discussing recent unpublished improvements to RIBALD. In general, successful interpretation depends on two factors: the number of lines, and whether or not the drawing can be classified as a member of special shape class (e.g. an extrusion or normalon). The state-of-the-art achieves correct interpretation of extrusions of any size and most normalons of 20—30 lines, but drawings of only 10—20 lines can be problematic for unclassified objects.Despite successes, there are caseswhere the desired interpretation is obvious to a human but cannot be determined by currently-available algorithms. We give examples both of our successes and of typical caseswhere human skill cannot be replicated.
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paper_title: Intuitive Shape Modeling by Shading Design

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Shading has a great impact to the human perception of 3D objects. Thus, in order to create or to deform a 3D object, it seems natural to manipulate its perceived shading. This paper presents a new solution for the software implementation of this idea. Our approach is based on the ability of a user to coarsely draw a shading, under different lighting directions. With this intuitive process, users can create or edit a height field (locally or globally), that will correspond to the drawn shading values. Moreover, we present the possibility to edit the shading intensity by means of a specular reflectance model.
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paper_title: Image-based object editing

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We examine the problem of editing complex 3D objects. We convert the problem of editing a 3D object of arbitrary size and surface properties to a problem of editing a 2D image. We allow the user to specify edits in both geometry and surface properties from any view and at any resolution they find convenient, regardless of the interactive rendering capability of their computer. We use specially-constrained shape from shading algorithms to convert a shaded image specified by the user into a 3D geometry.
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paper_title: Sculpting: an interactive volumetric modeling technique

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We present a new interactive modeling technique based on the notion of sculpting a solid material. A sculpting tool is controlled by a 3D input device and the material is represented by voxel data; the tool acts by modifying the values in the voxel array, much as a "paint" program's "paintbrush" modifies bitmap values. The voxel data is converted to a polygonal surface using a "marching-cubes" algorithm; since the modifications to the voxel data are local, we accelerate this computation by an incremental algorithm and accelerate the display by using a special data structure for determining which polygons must be redrawn in a particular screen region. We provide a variety of tools: one that cuts away material, one that adds material, a "sandpaper" tool, a "heat gun," etc. The technique provides an intuitive direct interaction, as if the user were working with clay or wax. The models created are free-form and may have complex topology; however, they are not precise, so the technique is appropriate for modeling a boulder or a tooth but not for modeling a crankshaft.
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paper_title: The BlobTree -- Warping, blending and boolean operations in an implicit surface modelling system

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Automatic blending has characterized the major advantage of implicit surface modeling systems. Recently, the introduction of deformations based on space warping and boolean operations between primitives has increased the usefulness of such systems. We propose a further enhancement which will greatly enhance the range of models that can be easily and intuitively defined with a skeletal implicit surface system. We decribe a hierarchical method which allows arbitrary compositions of models that make use of blending, warping and boolean operations. We call this structure the BlobTree. Blending and space warping are treated in the same way as union, difference and intersection, i.e. as nodes in the BlobTree. The traversal of the BlobTree is described along with two rendering algorithms; a polygonizer and a ray tracer. We present some examples of interesting models which can be made easily using our approach that would be very difficult to represent with conventional systems.
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paper_title: Adaptively sampled distance fields: a general representation of shape for computer graphics

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Adaptively Sampled Distance Fields (ADFs) are a unifying representation of shape that integrate numerous concepts in computer graphics including the representation of geometry and volume data and a broad range of processing operations such as rendering, sculpting, level-of-detail management, surface offsetting, collision detection, and color gamut correction. Its structure is uncomplicated and direct, but is especially effective for quality reconstruction of complex shapes, e.g., artistic and organic forms, precision parts, volumes, high order functions, and fractals. We characterize one implementation of ADFs, illustrating its utility on two diverse applications: 1) artistic carving of fine detail, and 2) representing and rendering volume data and volumetric effects. Other applications are briefly presented.
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paper_title: Practical volumetric sculpting

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We present here a sculpture metaphor for rapid shape-prototyping. The sculpted shape is the iso-surface of a scalar ﬁeld spatially sampled. The user can deposit material wherever he desires in space and then iteratively reﬁne it using a freeform tool. The tool shape can be designed inside the application. The tool can add, remove, paint or smooth material, or it can be used as a stamp to make prints on an existing shape. The user can move the scene and/or the tool with a Spacemouse (6D input device), or a 2D mouse using virtual trackball. We also focussed on the rendering quality, exploiting lighting variations, and environment textures that simulate high quality highlights on the surface. Both greatly enhance the shape estimation, which is in our opinion a crucial step during the design process. We also explored some stereo conﬁgurations to improve the user's perception of the spatial relationships between the elements of the scene. Our current implementation based on GLUT allows the application to run both on UNIX-based systems, such as IRIX and Linux, and on Windows systems. We obtain interactive response times, strongly related to the size of the tool. The performances issues and limitations are discussed.
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paper_title: Surface drawing: creating organic 3D shapes with the hand and tangible tools

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Surface Drawing is a system for creating organic 3D shapes in a manner which supports the needs and interests of artists. This medium facilitates the early stages of creative design which many 3D modeling programs neglect. Much like traditional media such as line drawing and painting, Surface Drawing lets users construct shapes through repeated marking. In our case, the hand is used to mark 3D space in a semi-immersive virtual environment. The interface is completed with tangible tools to edit and manipulate models. We introduce the use of tongs to move and scale 3D shapes and demonstrate a magnet tool which is comfortably held without restricting hand motion. We evaluated our system through collaboration with artists and designers, exhibition before hundreds of users, our own extensive exploration of the medium, and an informal user study. Response was especially positive from users with an artistic background.
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paper_title: Volume sculpting

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We present a modeling technique based on the metaphor of interactively sculpting complex 3D objects from a solid material, such as a block of wood or marble. The 3D model is represented in a 3D raster of voxels where each voxel stores local material property information such as color and texture. Sculpting is done by moving 3D voxel-based tools within the model. The affected regions are indicated directly on the 2D projected image of the 3D model. By reducing the complex operations between the 3D tool volume and the 3D model down to primitive voxel-by-voxel operations, coupled with the utilization of a localized ray casting for image updating, our sculpting tool achieves real-time interaction. Furthermore, volume sampling techniques and volume manipulations are employed to ensure that the process of sculpting does not introduce aliasing into the models.
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paper_title: A painting interface for interactive surface deformations

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A long-standing challenge in geometric modeling is providing a natural, intuitive interface for making local deformations to 3D surfaces. Previous approaches have provided either interactive manipulation or physical simulation to control surface deformations. In this paper, we investigate combining these two approaches with a painting interface that gives the user direct, local control over a physical simulation. The paint a user applies to the model defines its instantaneous surface velocity, the user can effect surface deformations. We have found that this painting metaphor gives the user direct, local control over surface deformations for several applications: creating new models, removing noise from existing models, and adding geometric texture to an existing surface at multiple scales.
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paper_title: Wires: a geometric deformation technique

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Finding effective interactive deformation techniques for complex geometric objects continues to be a challenging problem in modeling and animation. We present an approach that is inspired by armatures used by sculptors, in which wire curves give definition to an object and shape its deformable features. We also introduce domain curves that define the domain of deformation about an object. A wire together with a collection of domain curves provide a new basis for an implicit modeling primitive. Wires directly reflect object geometry, and as such they provide a coarse geometric representation of an object that can be created through sketching. Furthermore, the aggregate deformation from several wires is easy to define. We show that a single wire is an appealing direct manipulation deformation technique; we demonstrate that the combination of wires and domain curves provide a new way to outline the shape of an implicit volume in space; and we describe techniques for the aggregation of deformations resulting from multiple wires, domain curves and their interaction with each other and other deformation techniques. The power of our approach is illustrated using applications of animating figures with flexible articulations, modeling wrinkled surfaces and stitching geometry together.
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paper_title: Prototype Modeling from Sketched Silhouettes based on Convolution Surfaces

paper_content:

This paper presents a hybrid method for creating three-dimensional shapes by sketching silhouette curves. Given a silhouette curve, we approximate its medial axis as a set of line segments, and convolve a linearly weighted kernel along each segment. By summing the fields of all segments, an analytical convolution surface is obtained. The resulting generic shape has circular cross-section, but can be conveniently modified via sketched profile or shape parameters of a spatial transform. New components can be similarly designed by sketching on different projection planes. The convolution surface model lends itself to smooth merging between the overlapping components. Our method overcomes several limitations of previous sketched-based systems, including designing objects of arbitrary genus, objects with semi-sharp features, and the ability to easily generate variants of shapes.
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paper_title: Free-form Sketching with Variational Implicit Surfaces

paper_content:

With the advent of sketch-based methods for shape construction, there’s a new degree of power available in the rapid creation of approximate shapes. Sketch [Zeleznik, 1996] showed how a gesture-based modeler could be used to simplify conventional CSG-like shape creation. Teddy [Igarashi, 1999] extended this to more free-form models, getting much of its power from its "inflation" operation (which converted a simple closed curve in the plane into a 3D shape whose silhouette, from the current point of view, was that curve on the view plane) and from an elegant collection of gestures for attaching additional parts to a shape, cutting a shape, and deforming it. But despite the powerful collection of tools in Teddy, the underlying polygonal representation of shapes intrudes on the results in many places. In this paper, we discuss our preliminary efforts at using variational implicit surfaces [Turk, 2000] as a representation in a free-form modeler. We also discuss the implementation of several operations within this context, and a collection of user-interaction elements that work well together to make modeling interesting hierarchies simple. These include “stroke inflation” via implicit functions, blob-merging, automatic hierarchy construction, and local surface modification via silhouette oversketching. We demonstrate our results by creating several models.
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paper_title: A sketching interface for modeling the internal structures of 3D shapes

paper_content:

This paper presents a sketch-based modeling system for creating objects that have internal structures. The user input consists of hand-drawn sketches and the system automatically generates a volumetric model. The volumetric representation solves any self-intersection problems and enables the creation of models with a variety of topological structures, such as a torus or a hollow sphere. To specify internal structures, our system allows the user to cut the model temporarily and apply modeling operations to the exposed face. In addition, the user can draw multiple contours in the Create or Sweep stages. Our system also allows automatic rotation of the model so that the user does not need to perform frequent manual rotations. Our system is much simpler to implement than a surface-oriented system because no complicated mesh editing code is required. We observed that novice users could quickly create a variety of objects using our system.
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paper_title: An interface for sketching 3D curves

paper_content:

The ability to specify nonplanar 3D curves is of fundamental importance in 3D modeling and animation systems. Effective techniques for specifying such curves using 2D input devices are desirable, but existing methods typically require the user to edit the curve from several viewpoints. We present a novel method for specifying 3D curves with 2D input from a single viewpoint. The user rst draws the curve as it appears from the current viewpoint, and then draws its shadow on the oor plane. The system correlates the curve with its shadow to compute the curve's 3D shape. This method is more natural than existing methods in that it leverages skills that many artists and designers have developed from work with pencil and paper.
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paper_title: A suggestive interface for image guided 3D sketching

paper_content:

We present an image guided pen-based suggestive interface for sketching 3D wireframe models. Rather than starting from a blank canvas, existing 2D images of similar objects serve as a guide to the user. Image based filters enable attraction, smoothing, and resampling of input curves, and allows for their selective application using pinning and gluing techniques. New input strokes also invoke suggestions of relevant geometry that can be used, reducing the need to explicitly draw all parts of the new model. All suggestions appear in-place with the model being built, in the user's focal attention space. A curve matching algorithm seamlessly augments basic suggestions with more complex ones from a database populated with previously used geometry. The interface also incorporates gestural command input, and interaction techniques for camera controls that enable smooth transitions between orthographic and perspective views.
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paper_title: Interaction techniques for 3D modeling on large displays

paper_content:

We present an alternate interface for 3D modeling for use on large scale displays. The interface integrates several concepts specifically selected and enhanced for large scale interaction. These include 2D construction planes spatially integrated in a 3D volume, enhanced orthographic views, smooth transitions between 2D and 3D views, tape drawing as the primary curve and line creation technique, visual viewpoint markers, and continuous twohanded interaction.
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paper_title: A multi-layered architecture for sketch-based interaction within virtual environments

paper_content:

Abstract In this article, we describe a multi-layered architecture for sketch-based interaction within virtual environments. Our architecture consists of eight hierarchically arranged layers that are described by giving examples of how they are implemented and how they interact. Focusing on table-like projection systems (such as Virtual Tables or Responsive Workbenches) as human-centered output-devices, we show examples of how to integrate parts or all of the architecture into existing domain-specific applications — rather than realizing new general sketch applications — to make sketching an integral part of the next-generation human–computer interface.
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paper_title: Harold: a world made of drawings

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The problem of interactively creating 3D scenes from 2D input is a compelling one, and recent progress has been exciting. We present our system, Harold, which combines ideas from existing techniques and introduces new concepts to make an interactive system for creating 3D worlds. The interface paradigm in Harold is drawing :a ll objects are created simply by drawing them with a 2D input device. Most of the 3D objects in Harold are collections of planar strokes that are reoriented in a view-dependent way as the camera moves through the world. Virtual worlds created in Harold are rendered with a stroke-based system so that a world will maintain a hand-drawn appearance as the user navigates through it. Harold is not suitable for representing certain classes of 3D objects, especially geometrically regular or extremely asymmetric objects. However, Harold supports a large enough class of objects that a user can rapidly create expressive and visually rich 3D worlds.
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paper_title: Drawing for Illustration and Annotation in 3D

paper_content:

We present a system for sketching in 3D, which strives to preserve the degree of expression, imagination, and simplicity of use achieved by 2D drawing. Our system directly uses user-drawn strokes to infer the sketches representing the same scene from different viewpoints, rather than attempting to reconstruct a 3D model. This is achieved by interpreting strokes as indications of a local surface silhouette or contour. Strokes thus deform and disappear progressively as we move away from the original viewpoint. They may be occluded by objects indicated by other strokes, or, in contrast, be drawn above such objects. The user draws on a plane which can be positioned explicitly or relative to other objects or strokes in the sketch. Our system is interactive, since we use fast algorithms and graphics hardware for rendering. We present applications to education, design, architecture and fashion, where 3D sketches can be used alone or as an annotation of an existing 3D model.
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paper_title: Creating principal 3D curves with digital tape drawing

paper_content:

Previous systems have explored the challenges of designing an interface for automotive styling which combine the metaphor of 2D drawing using physical tape with the simultaneous creation and management of a corresponding virtual 3D model. These systems have been limited to only 2D planar curves while typically the principal characteristic curves of an automotive design are three dimensional and non-planar. We present a system which addresses this limitation. Our system allows a designer to construct these non-planar 3D curves by drawing a series of 2D curves using the 2D tape drawing technique and interaction style. These results are generally applicable to the interface design of 3D modeling applications and also to the design of arm's length interaction on large scale display systems
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paper_title: FreeDrawer: a free-form sketching system on the responsive workbench

paper_content:

A sketching system for spline-based free-form surfaces on the Responsive Workbench is presented. We propose 3D tools for curve drawing and deformation techniques for curves and surfaces, adapted to the needs of designers. The user directly draws curves in the virtual environment, using a tracked stylus as an input device. A curve network can be formed, describing the skeleton of a virtual model. The non-dominant hand positions and orients the model while the dominant hand uses the editing tools. The curves and the resulting skinning surfaces can interactively be deformed.
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paper_title: 3D Sketching with profile curves

paper_content:

In recent years, 3D sketching has gained popularity as an efficient alternative to conventional 3D geometric modeling for rapid prototyping, as it allows the user to intuitively generate a large range of different shapes. In this paper, we present some sketching interactions for 3D modeling, based on a set of two different bidimensional sketches (profile curve and silhouette curve). By using these two sketches and combining them with a gesture grammar, a very large variety of shapes (including shapes with topological holes) can be easily produced by our interactive modeling environment.
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paper_title: Sketch-based modeling with few strokes

paper_content:

We present a novel sketch-based system for the interactive modeling of a variety of free-form 3D objects using just a few strokes. Our technique is inspired by the traditional illustration strategy for depicting 3D forms where the basic geometric forms of the subjects are identified, sketched and progressively refined using few key strokes. We introduce two parametric surfaces, rotational and cross sectional blending, that are inspired by this illustration technique. We also describe orthogonal deformation and cross sectional oversketching as editing tools to complement our modeling techniques. Examples with models ranging from cartoon style to botanical illustration demonstrate the capabilities of our system.
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Title: A survey of sketch-based 3-D modeling techniques

Section 1: Introduction
Description 1: Provide an overview of the increasing demand for 3-D modeling, the challenges with traditional modeling techniques, and the emergence of sketch-based modeling as an intuitive solution.

Section 2: The practice of sketching
Description 2: Define sketching, discuss its importance in the creative process, and explain the components of traditional sketching such as feedback, overdrawing, and incremental refinement.

Section 3: Why sketch-based modeling?
Description 3: Explain the reasons for using sketching as a basis for 3-D modeling, touching on its importance in the creative process and its applicability to 3-D modeling interfaces.

Section 4: Sketch input
Description 4: Discuss the hardware and software requirements for sketch-based modeling, focusing on digitizing tablets, line creation, and issues related to overdrawing.

Section 5: Sketch-based modeling methods
Description 5: Provide an overview of various sketch-based modeling techniques, categorized into seven classifications with detailed examples of each.

Section 5.1: Gesture created primitives
Description 5.1: Explain how drawing input is interpreted as gestures for creating basic shapes and the evolution of this approach with examples.

Section 5.2: Reconstruction
Description 5.2: Discuss methods for directly interpreting users' drawings into 3-D shapes, touching on the challenges and techniques like Huffman-Clowes line labeling.

Section 5.3: Height-fields and shape from shading
Description 5.3: Explain how shading information is used to infer 3-D geometry and the related techniques such as height-fields and shape from shading.

Section 5.4: Deformation and sculpture
Description 5.4: Describe techniques that involve deforming 3-D models as if sculpting, including global and local deformations, and related applications.

Section 5.5: Blobby inflation
Description 5.5: Provide an overview of systems that use inflation techniques to create 3-D models from 2-D silhouette drawings, with examples like Teddy.

Section 5.6: Contour curves and drawing surfaces
Description 5.6: Discuss methods for using 2-D drawing input to create 3-D curves and surfaces, including the use of drawing planes and fully 3-D space curves.

Section 5.7: Stroke based constructions
Description 5.7: Describe systems that use strokes to create and manipulate 3-D surfaces and volumes, providing examples of parametric surfaces and procedural modeling methods.

Section 6: Discussion
Description 6: Summarize the observations from previous sections, including the role of 2-D input in 3-D modeling, the expressivity and ambiguity of sketching, and the challenges and prospects of sketch-based modeling interfaces.

Section 7: Conclusion
Description 7: Conclude by summarizing the key points discussed in the paper, emphasizing the potential future directions for sketch-based 3-D modeling techniques.