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1484 # 2003 International Union of Crystallography � Printed in Great Britain ± all rights reserved J. Appl. Cryst. (2003). 36, 1484±1485
computer program abstracts
Journal of
AppliedCrystallography
ISSN 0021-8898
computer program abstractsThis category provides a rapid means of communicating up-to-date information concerning both new programs or systems
and significant updates to existing ones. Submissions should follow the standard format given in J. Appl. Cryst. (1985). 18,
189±190, also available from Crystallography Journals Online at http://journals.iucr.org/j/services/authorservices.html.
MCE±CAVE: program for interactivevisualization of electron density mapswithin the CAVE virtual-reality environ-ment
Michal HusÏaÂk,a,b* Christoph Anthesc and Paul
Heinzlreiterc
aDepartment of Solid State Chemistry, Institute of Chemical Technology Prague,
Technicka 5, 166 28 Prague 6, Czech Republic, bInstitute of Physical Biology, NovyÂ
ZaÂmek 136, 373 33 Nove Hrady, Czech Republic, and cDepartment for Graphics
and Parallel Processing (GUP), Institute of Technical Computer Science and
Telematics, Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz,
Austria. Correspondence e-mail: husakm@vscht.cz
Received 19 August 2003
Accepted 23 September 2003
Keywords: electron densities; visualization; virtual reality
1. The crystallographic problem
It is dif®cult to interpret electron densities or similar maps without a
sophisticated method of visualization. We have developed experi-
mental software for the visualization of such data by the help of a
multi-projection virtual reality (VR) device: the CAVE (Cave
Automatic Virtual Environment) (Cruz-Neira et al., 1992).
2. Method of solution
The code is a modi®ed version of MCE software (HusÏaÂk &
KratochvõÂl, 2003) and therefore is able to process the same type of
data. The required source information is a pre-computed voxel map
generated by solution software for small molecular structures, such as
CRYSTALS (Watkin et al., 2002) and SHELX, in combination with
WinGX (Farrugia, 1999).
3. Software environment
The code is written in C++. The CAVElib3.0 and GLUT3.7 libraries
were used. CAVElib is a common interface for displaying a graphical
application in a CAVE. It additionally handles basic interaction
functionalities. The code using CAVElib was designed to run under
Irix 6.5. A demo version emulating the CAVE environment running
under Win32-based operating systems uses the GLUT library only.
4. Hardware environment
The code was tested with a four-wall stereo-projection CAVE device
driven by an SGI Origin 3800 equipped with 128 400 MHz processors.
The graphics are rendered in parallel by two In®nite Reality graphics
boards. The user position is tracked by an Ascension MotionStar
tracking system (magnetic tracking). To achieve the three-dimen-
sional impression, CrystalEye stereoscopic shutter glasses are used. A
6DOF (six degrees of freedom) tracked wand with an additional
controller on top is used for interaction.
The simpli®ed PC code version, with the built-in CAVE emulator,
requires a graphics card with OpenGL hardware support. It is also
possible to use a graphics card supporting stereoscopic display.
Additionally, a joystick may be used for interaction.
5. Program specification
The code uses CAVElib for visualization of molecular structures and
electron density maps on the multiple stereo-projection walls of the
Figure 1Screenshot from the PC CAVE emulator showing a molecule in a CAVE devicemodel.
Figure 2Photograph of a user inside the CAVE device surrounded by the electron densitymaps.
J. Appl. Cryst. (2003). 36, 1484±1485 Michal HusÏaÂk et al. � MCE±CAVE 1485
computer program abstracts
CAVE device (Fig. 1). The user is placed inside the virtual-reality
model of the structure, surrounded by the maps and the molecule
(Fig. 2). The perspective and stereoscopic parameters of the view are
calculated according to the motion-tracked head position. It is
possible to manipulate the molecule and the maps by use of the wand
or the controller. Adding new peaks to the map is also possible. The
positions of new peaks are derived from the 6DOF tracking of the
user's hand-held navigation device.
For the programming it was necessary to modify the C++ code for
simultaneous parallel processing on multiple synchronized graphics
pipelines and for support of multiple CPUs.
The main purpose of the code was to test the CAVE device as a
suitable output device for crystallographic visualization. During the
design of the application, the main problem emerging was the
development of a user-friendly interaction model for the VR envir-
onment. In comparison with the original MCE code (HusÏaÂk &
KratochvõÂl, 2003), it was necessary to use a totally different method
for user interaction with respect to model manipulation and map
adjustment. The implementation of very sophisticated methods of
interaction based on a combination of position tracking and voice
recognition is under current development.
The feeling of presence within the model created by the CAVE
delivers signi®cant bene®t in understanding and manipulating the
displayed structure. Nevertheless, some drawbacks compared with a
desktop environment using a mouse as an input device arise from the
cost and space requirements for the CAVE system.
6. Documentation
The distribution contains a text ®le describing the basic functions. The
source data format is identical to that of the MCE code. Further
details are available on the distribution Web page (see below).
7. Availability
The MCE±CAVE application for Irix 6.5, using CAVElib3.0, is
available free of charge as Irix source code and as a binary execu-
table. The version with a built-in CAVE emulator for Win32-based
operating systems is also available as source code and a binary
executable. The download location for both versions is: http://
www.ccp14.ac.uk/ccp/web-mirrors/marchingcube-fourierviewer/
~husakm/Public/MarchingCubeELD/MarchingCubeELD.htm.
The work on the software development was supported by the
Grant Agency of the Czech Republic, grants 203/01/0700, GV203/98/
K023, and the projects LN00A141, MSM12300001 of the Czech
Ministry of Education.
References
Cruz-Neira, C., Sandin, D. J., DeFanti, T. A., Kenyon, R. V. & Hart, J. C.(1992). Commun. ACM, 35(6), 64±72.
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837±838.HusÏaÂk, M. & KratochvõÂl, B. (2003). J. Appl. Cryst. 36, 1104.Watkin, D. J., Prout, C. K., Carruthers, J. R., Betteridge, P. W. & Cooper, R. I.
(2002). CRYSTALS, Issue 11, Chemical Crystallography Laboratory,University of Oxford.
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