Sketching Free-Forms in Semi-Immersive Virtual Environments

Fraunhofer InstitutGraphischeDatenverarbeitung

IGD-A2 André Stork Oliver SchimpkeRaffaele De Amicis

Sketching Free-Forms in Semi-Immersive Virtual

EnvironmentsRaffaele de Amicis Raffaele de Amicis

André StorkAndré StorkOliver SchimpkeOliver Schimpke

Fraunhofer Institute for Computer Graphics (IGD) Fraunhofer Institute for Computer Graphics (IGD) Department for Industrial ApplicationsDepartment for Industrial Applications

Rundeturmstraße 6Rundeturmstraße 664283 Darmstadt64283 Darmstadt

http://www.igd.fhg.de/igd-a2/http://www.igd.fhg.de/igd-a2/



Overview• Introduction• Related work• Hardware and system set-up• Free-form sketching methods

– Coons patches with just one stroke– Skinning with immediate preview– Net-surfaces– Symmetric surfaces– Trimming

• Conclusions and future work



• Difficulties are encountered in the styling phase of the design process when free-form surfaces (shortly free-forms) have to be modelled.• The styling phase is still determined by clay models, only later in the process CAS systems are used.• The industry is looking for easy to use fee-form sketchers in virtual environments that narrow the gap between human beings and computer.

Introduction



• Starting point:There are well known free-form surface concepts(Coons patches, skinning, etc.) but they require

muchknowledge on the user’s side.

• Main questions:• How to build up an intuitive user-interface to these free-form surface modelling techniques ?• How to map the sketched data to the algorithms behind these techniques ?

Introduction



• Prerequisites:• We want to follow a line-oriented approach where the user sketches lines in free space. This follows the way designers think and work, especially those in the automotive industry.• We don’t want to cope with control points: the user shall be enabled to draw a surface in free space.• We want to generate surfaces that can be post-processed by commercial tools.

Introduction



Related Work• 3-Draw: A tool for designing 3D shapes.

E. Sachs, A. Roberts, and D. Stoops. No visual correspondence

• Free-Form Surface Design in a Virtual Environment.T. H. Dani, L. Wang, R. Gadh. Interaction with control points

• Surface Drawing, Schroeder et al.Drawing polygonal structures in 3D at VT using a glove

• Multiple-Points Constraints based Deformationfor Free-Form Surfaces. J.M. Zheng, K.W. Chan, I Gibson. Deform sketched regions with 2D input

• etc.



Virtual Pad

Object under construction

Pen

Transparent physical pad

User at the Virtual Table

Hardware setup



Why Virtual Tables?

• direct 3D input in the space over the tabletop • lightweight interaction devices• integratable in the daily work process (much better than HMDs, CAVEs, gloves)• support of the ‚Walk-Up VR‘ concept

Hardware setup



Free Form Surface Sketching

• Coons Patches• Net-Surfaces• Skinned Surfaces• Trimming• Mirror Mode



Coons Patches from only one outline stroke

3D outline stroke with shadow projection onto virtual walls

• Coons patches are defined by two pairs of curves, one in u and v direction respectively.• To ease the input process, we want to derive them from just one outline stroke.• BUT, how to split it up?




Splitting contour by WC bounding box

Splitting contour uniformely in u,v space

Splitting contour by min. bounding box



Skinned Surfaces• are usually defined by a set of similarly oriented curves • by laying a ‚skin‘ over the curves the surface is defined• usually the user has to input the curves and has no impression of the final surface until the interpolation is done

To overcome these problems, we introduced:• preview by polygonal visual feedback• adaptive point insertion technique

The potential of skinned surfaces is better accessible.



Skinned Surfaces withimmediate feedback



Net-Surfaces• allow to better control the inner shape of a free-form surface• but the approximation algorithm wants the curves directed and ordered which hinders the user’s flexibility when inputing the curves

341

61

2

51

11

This is how the user wantsto input the curves(any order, any direction)

Sketch of a car bodyusing a net-surface



Net-Surfaces• so, we determine the plane ‘over’ which the curves are defined• sort the curves along the major directions of the plane (u and v)• and redirect them, so that point in the same direction• finally, we feed the net-surface approximation algorithm to generate the free-form surface

Kurvennetz

Vektoren zwischenprojizierten Kurven-endpunkten

Ebene mit max. Summe der Länge

vectors between projected curve endpoints

curve net

plane with max. sum of vector lengths

Sorting algorithm Case that is not handled correctly by our sorting



Net-Surfaces



Mirror Mode

A symmetric coons patch using the pad

as a mirror

• Many industrial products are symmetric.• Instead of drawing only one half and mirror it afterwards, we designed a two-handed technique that creates a symmetric surfaces while drawing the curve(s) by using the palette as virtual mirror.



Trimming

• Up to now, we used direct 3D interaction, for trimming this is hardly possible. • Therefore, this time the pen sends a ray into the scene to define the trim curve.



Subtractive Sweeping ...

... is not exactly a free-form surface sketching technique, but a means to shape volumes by removing (or adding) material. A real-time rendering techniques immediately shows the result.



• Intuitive free-form sketching techniques• Releasing the user from mathematical knowledge • Characteristic lines• 2-handed interaction with pad and pen

• Direct 3D interaction techniques and 3D visualization• Correspondence between hand movement and visual feedback• Walk-up VR-concept• Lightweight interaction devices

Conclusion



• Free Form deformation techniques (in combination with the palette),• Users studies and discussion groups,• Evaluation of alternative input devices and tracking technology,

… to render the Virtual Table to its full potential as a modeling workspace.

Future Work



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Sketching Free-Forms in Semi-Immersive Virtual Environments

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