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.