Rear-projection-based Full Solid Angle Display

(from ICAT'96 Proceeding)

Hiroo IWATA

Institute of Engineering Mechanics, University of Tsukuba,Tsukuba,305 JAPAN

ABSTRACT

This paper presents design method of rear-projection based cokes surface display for ultimate visual immersion. The display consists of a closed polyhedron screen. A viewer stands inside the polyhedron so that image covers full solid angle around the viewer. Optimum configuration of polyhedron is determined by two criteria: pixel efficiency. Through examination of these criteria, rhombic dodecahedron is chosen. We built dodecahedron screen with twelve projecters in which a viewer can stand. Space requirement of the display is 2.6m(D)x2.6m(W)x2.7m(H) so that it can be built isn a normal size room.


1. Introduction

Visual immersion plays an important roll in virtual environment. A head-mounted display (HMD) provides full solid angle view of virtual space . However, field of view of HMD is limited because of its optical system. Field of view of human eye is approximately 200 degrees(lateral) and 125 degrees(vertical). Is is difficult to develop head-mounted optical system which covers all the field of view. A large screen is used for virtual environment as an altenative of HMD. A dome screen or a cubic screen are proposed for the altanatives. Those screens requires theater-like large space, which restricts its general use for computer-human interaction. Moreover, existing configuration of large screen systems do not cover full solid angle around the viewer. This paper discusses about design of closed surface display which covers full solid angle. We set criteria in order to optimize space utility of the display system. The result shows that a closed surface display in which a viewer stands can be built in a normal size room.


2. Related Works on Closed Surface Display

2-1.Dome Screen

A dome screen provides a planetarium-like picture which covers large field of view. OMNIMAX theater si a typical display system of a dome screen[1]. However, planetarium-like projection system cannot cover full solid angle of the viewer. If two domes are connected to make a closed surface display, there is no room for the viewer.

2-2. CAVE

A cubic screen that surrounds a viewer is well known as the CAVE[2]. The CAVE is composed of four square screens. Those screens cover two third of full solid angle. The CAVE can be extended to a closed surface display by using six square screens. Problem of this configuration is discussed later.

2-3. Display without projecters

If closed surface is composed of light emitting device such as LED of fiber optics, spherical display which covers full solid angle can be constructed. Those specialized hardware is fairly difficult to develop and it leads to high cost. Closed surface display proposed in this paper is based on normal projecters.


3. Rear-projection Polyhedron Screen

Spherical screen is ideal for covering wide field of view. However, fornt-projection system normally used cor spherical screen is impossible to extend to closed surface display. In case of such configuration, volume of projecters obstruct image on screen. For this reason, closed surface display must be composed of rear-projection screen.

Rear-projection screen must be divided into polygons. Thus, the shape of the closed surface display is polynedron. There ard many types of polyhedrons. The emphasis of this paper is which polyhedron is most suitable for the closed surface display. We set two criteria for determination of optimum configuration of polyhedron: pixel efficiecy and space efficiency. We studied geometry of polyhedrons form these point of views[3][4]. Considering easiness of construction, such as number of projecters and independent display channels, this paper limits number of polygon of polyhedron up to 16.


4. Criteria 1: Pixel Efficiency

Aspect ratio of projected image ans crame buffer of display channel is 4:3. Pixel efficiency means how many pixels from a projecter are displayed ofn each polygon of the polyhedron. Typical polygons which consists polyhedrons are regular triangle, regular square, rhombus, pentagon and hexagon. We examined pixel efficiency of those polygons. Figure 1 shows dead pixel of rhombus.

Figure 1. Dead pixels of rhombus

Pixel efficiency is determined by rationof display pixels. Results of calculation of pixel efficiency are: