Methods to Calibrate Projection Transformation Parameters for See-Through Head-Mounted Displays

Abstract

See-through head-mounted displays (STHMDs), which superimpose the virtual environment generated by computer graphics (CG) on the real world, are expected to be able to vividly display various simulations and designs by using both the real environment and the virtual environment around us. However, we must ensure that the virtual environment is superimposed exactly on the real environment because both environments are visible. Disagreement in matching locations and size between real and virtual objects is likely to occur between the world coordinates of the real environment where the STHMD user actually exists and those of the virtual environment described as parameters of CG. This disagreement directly causes displacement of locations where virtual objects are superimposed. The STHMD must be calibrated so that the virtual environment is superimposed properly. Among the causes of such errors, we focus both on systematic errors of projection transformation parameters caused in manufacturing and differences between actual and supposed location of user's eye on STHMD when in use, and propose a calibration method to eliminate these effects. In the calibration method, the virtual cursor drawn in the virtual environment is directly fitted onto targets in the real environment. Based on the result of fitting, the least-squares method identifies values of the parameters that minimize differences between locations of the virtual cursor in the virtual environment and targets in the real environment. After we describe the calibration methods, we also report the result of this application to the STHMD that we have made. The result is accurate enough to prove the effectiveness of the calibration methods.

Measurement of auditory alleys in a virtual environment and their mathematical models

“…The STHMD, in which the virtual environment can be superimposed on the real environment by a beam splitter, can be calibrated to make the coordinates of the visual space for a virtual environment coincide with those of the visual space for a real environment by the superimposition. A calibration method was developed and applied to the visual parameters of the STHMD to eliminate errors caused by mechanical misalignments in the STHMD [11] and by individual differences between actual and designed location of pupils of eyes, which ensured the coincidence of the apparent distance in a virtual environment with that in the real environment [12]. Using one of the computers, auditory signals were synthesized, output through DSP, and input through headphones (Senheiser HD25SP) to both ears of the subject.…”

Occlusion in collaborative augmented environments

“…The problem of registering the users head position with the position of the virtual camera and the virtual objects with the real environment has already been covered extensively [AZ94,ST96a,TA96,WH95]. Here -like in the previously cited approach to occlusion by [BE97] -a 2D image-based approach presented by Kutulakos [KU98] seems to be an adequate solution for video-based systems.…”

A new system for online quantitative evaluation of optical see-through augmentation

“…Tuceryan and Navab present a user-friendly calibration method for optical see-through HMDs [29]. Oisho and Tachi discuss the calibration of a rigidly mounted optical see-through display [26]. MacIntyre and Coelho describe a method for adapting to the level of tracking error for AR systems [20].…”