Design
Issues of Relief Maps for Haptic Displays
|
Christian Springsguth Multimedia Campus Kiel |
Gerhard Weber University of Kiel - MMC |
Abstract
Tactile relief maps and use of physical small-scale mock-ups of
buildings or statues are well-known to blind and deaf blind people. We design
3D-models of sightseeing landmarks for haptic presentation and integrate them into
2.5D virtual relief maps. The VRMLTourGuide was developed as a part of the
Wernigerode Tour Guide, which is a multimedia document describing the medieval
city of Wernigerode. With focus on blind people the application development
resulted in a browser system, which facilitates haptic exploration of 3D-structures
in the context of a relief map. Through synthetic speech users can receive
historical and touristic descriptions for additional non-visual information.
1
Introduction
The Multireader
Project aims at heterogeneous print disabled reader groups reading multimedia
documents. While audiobooks make use of structured time-depend media, titles
integrating graphics, video or audio are largely inaccessible to visually
impaired people. In this paper the focus is especially on the user group of
blind and deaf blind people. For these users accessibility of graphics is the
main problem while using multimedia documents. One field of application using
graphics is displaying virtual maps. During the development of the Wernigerode
Tourist Guide, touristic maps will be made accessible to blind and deaf blind
people using haptic exploration.
2
Tactile graphics
Paper-based
drawings may be felt with fingers if appropriate ink is applied to paper
(Lange, 2001), paper partially is swollen (Eccles, 2002), or paper is embossed
to produce relief structures. Paper’s advantage over transitory Braille
displays is provision of a flat and large surface with partially rising 3D-structures.
Nevertheless play the kind of paper, the tactile properties of ink, and the
design of embossings an important role in acceptance of tactile graphics. One
of the recent developments to automatically and economically produce tactile
drawings is based on the capability of mechanical printers to emboss dots
within a fine-grained grid of equidistant points (Walsh and Gardner, 2001).
Thermoform
production of plastic foils overcomes limitations of paper to include tall relief
structures. However we want to refer to these models as reliefs or 2.5D-models
as no convex vertical structure can be produced. Based on the thermoform
technology, deepening of plastic foil in vacuum must not exceed a few
centimetres. Recently CAD driven encarved wooden negatives have been developed,
but manual construction using paper, wires of various diameters and other heat
resistant materials still is more economic.
The turn
around time between design of a model and being able to read it, is too long to
be able to design an interactive system in most cases. Also, multimodal systems
combining tactile graphics with pointing and acoustic feedback are bound to
this restriction.
3 Designing Virtual
Haptic Maps
For the
average sighted person virtual maps become more and more important. Such maps
can be easily distributed and updated for example via the Internet. Other
advantages of electronic maps are:
· they are almost freely
zoomable
·
the degree of details
is adjustable,
·
information, which is
visible in the map is selectable.
But these
electronic, virtual maps are neither usable nor accessible for blind people.
We created a
virtual tactile map of the city of Wernigerode. The map is integrated in the
Wernigerode Tour Guide as an SVG graphics (see Figure 1). In the following we describe how this is
transformed into a tactile map.
Figure 1: Sample map of the town of Wernigerode, where 11 is the town hall and 15 the castle
First step
was to design a 3D-world with streets, special buildings, railroads and a
river. According to prior research, the streets are not modelled as elevated
lines like in usual tactile maps. The streets were modelled as grooves between
blocks of houses (Ramloll et al., 2001). Ramloll et al. showed people can
follow engraved virtual lines much better than elevated lines. To feel the map
haptically the SensAble PHANToM is used. Compared to other force feedback
devices like the PANTOGRAPH (Ramstein et al. 1994) the virtue of the PHANToM
are its three degrees of freedom supporting force feedback. Its ability to
render 3D-objects haptically is necessary to display the relief-like virtual
map. There are some difference between a virtual haptic 3D-display and a
tactile relief map. The advantages of general virtual maps compared to usual paper-based
maps as described above are applicable to a virtual haptic 3D-display as well. For
example, it is possible to zoom into the map and a particular clipping can be
chosen, too.
To generate a
3D-model, which is displayable with the application using the PHANToM, a 3D-modelling
software is used (see Figure
2 b). This software must be able to simplify the
physical structure (see Figure
2 a), place the 3D models onto a map, and to export the
3D-world as a VRML 2.0 formatted file. For import of the VRML file a
VRML-parser (König et al., 2000) is being used. Further, the combined 2.5D
and 3D-model must be enriched by additional information about the map itself,
buildings, sights and other objects inside the map.
Figure 2: (a) Photograph and (b) model of the town hall of Wernigerode
Haptically
exploring the shape of a smaller physical model is the traditional and well
accepted way for blind and deaf blind people to build up their own model of a
building. The difference between virtual and physical exploration of a shape
is, that with the PHANToM people only have one contact point between themselves
and the virtual object. For physical models people can use both hands with all
fingers to scan an object.
An advantage
of a virtual haptic 3D-map is the possibility to combine 2.5D and 3D-structures
while working with the map. Due to the limitations of the material used for
tactile maps, people can feel lines, flat shapes and Braille printings. With a
virtual haptic 3D-mapping and the 3D-environment these limitations may be
overcome. The concomitance of touchable streets, railroads, rivers and
integrated detailed models of some of the landmarks introduces a common concept
of more graphical touristic maps. The
possibility to choose special viewpoints allows users to adjust the degree of
displayed details (see Figure 3).
The use of a
3D-environment leads to the ability to display very unusual structures. So it is
possible to integrate very high towers or buildings into a relief map. In
addition convex shapes can be easily modelled and afterwards haptically
explored, too. Good examples for this shapes would be large gateways or
buildings with an overhanging roof.
To
prevent people from losing contact to the surface of a virtual object force
fields and contact forces are used. Contact forces apply to the PHANToM, when it
has direct contact to an object. Force fields work like magnetic fields and
apply to the PHANToM, when it is moved inside an object surrounding volume.
These force fields help users to find an object if contact has been lost. With
help of these forces it is easier to stay in contact with a virtual object or to
find an object, if someone has lost contact to it. Another help for blind people
exploring a virtual map is audio support. Information concerning navigation and
orientation within the map are provided to the user via synthetic speech output.
Further information describing special buildings or sights and their different
parts or sections are provided as well.
Figure 3: Enlarged view of the town hall All
2.5D and 3D-components of the relief map have been designed to increase usability while working with the PHANToM. The map is based on a ground layer, where all other elements are located on (see Figure 4). To construct railroads and rivers special structures have been developed,
Figure 4: VRMLTourGuide with a relief map of Wernigerode including castle and town hall
to which
textures can be applied. This is important to recognise differences between
them and streets. The river for example is modelled using a typical waveform.
During evaluation these special structures and textures will be reviewed as
well as the size of the blocks of houses and the depth of the grooves
representing streets.
4
Conclusion The
combined use of a 3D-capable force feedback device like the SensAble PHANToM, a
3D- graphics environment and audio support through synthetic speech output
results in a system, which will allow blind people to benefit from the
advantages virtual maps deliver and the advantages tactile graphics have for
blind people. More work on the design of mixed relief structures and 3D-models
is necessary to adjust the complexity to the users. 
5
Acknowledgements
The
Multireader Project is funded under the IST Programme by the Commission of the
European Communities (Project IST-2000-27513). The Consortium consists of the
City University London (United Kingdom), the Electrotechnical Engineering
Department (ESAT) of the Katholieke Universiteit Leuven (Belgium), the Royal
National Institute for the Blind (United Kingdom), the Federation of Dutch
Libraries for the Blind (the Netherlands), the Harz University of Applied
Studies (Germany) and Pragma (The Netherlands). The VRML-parser was developed
by Jochen Schneider and Henry König.
6
References
Eccles, Philip
(2002). The Technology Behind Swell Paper. 2nd International Conference on Tactile
Diagrams Maps and Pictures 2002; (Hatfield, UK 19.-21. June 2002), National
Center on Tactile Diagrams, Hatfield, UK.
König, Henry; Schneider, Jochen; Strothotte, Thomas (2000). Haptic exploration of virtual buildings
using non-realistic rendering. International
Conference on Computers Helping People with Special Needs (Karlsruhe,
17.-21. July 2000), München: Oldenbourg, 377-384.
Lange, Max (2001). Tactile
Graphics – as easy as that! Proceedings of the 1999 CSUN International
Conference on Technology and Persons with Disabilities, Los Angeles, CA, 1999 http://www.csun.edu/cod/conf/1999/proceedings/session0168.htm.
Ramloll, Rameshsharma; Yu, Wai;
Brewster, Stephen A.; Riedel, Beate; Burton, Mike; Dimigen, Gisela (2000). Constructing sonified haptic line graphs for the blind student:
first steps. In Proceedings of ACM Assets
2000 (Arlington, VA, 13.-15. November 2000), New York: ACM Press, 17-25.
Ramstein, Christophe,
Hayward, Vincent (1994). The PANTOGRAPH: a large workspace haptic device for a
multi-modal human-computer interaction. CHI
94 Companion on Human Factors in Computing Systems, Boston, Massachusetts
USA, ACM Press:New York, 57 - 58.
Walsh,
Patricia and Gardner, John A. (2001). TIGER, A NEW
AGE OF TACTILE TEXT AND GRAPHICS. Proceedings
of the 2001 CSUN International Conference on Technology and Persons with
Disabilities, Los Angeles, CA, http://www.csun.edu/cod/conf2001/proceedings/0128walsh.html.