Calibration Method of Visual Parameters for See-Through Head-Mounted Display.

Abstract

It is expected that See Through Head-Mounted Display (STHMD) , which superimposes the virtual environment generated by computer graphics (CG) on the real world, can vividly execute various simulations and designs by using both of the real and virtual environment around us. In STHMDs, information given as a virtual environment has to exactly match with the real environment, because both environments are visible. This is one of the problems to be solved for practical use. Particularly for matching of locations and size between real and virtual objects, disaccordance is likely to occur between the world coordinate of the real environment where the user of STHMD actually exists and that of the virtual environment described as parameters of CG, which directly causes displacement of locations where virtual objects are superimposed.This must be calibrated so that the virtual environment is superimposed properly. Among causes of such errors, we focused both on systematic errors of visual parameters caused in manufacturing process and differences between actual and supposed location of user's eye on STHMD when in use. The former is required to be calibrated only once after the fabrication of STHMDs, whereas the latter has to be calibrated every time users start using STHMDs. We have proposed calibration methods which are suitable to properties of these causes of errors. In the method, the direct fitting of the virtual cursor drawn in the virtual environment onto targets in the real environment is performed. Then, based on the result of fitting, the least square method identifies values of the visual parameters which minimize differences between locations of virtual cursor in the virutal environment and targets in the real environment. Application of the method to the STHMD which we have made is also repored. The differences between the virtal cursor and targets in the real environment due to systematic errors caused in the manufacturing process were reduced to about 1 [mm] per target, which was less than one-thirtieth of that before the calibration. The differences between the virtual cursor and targets in the real environment due to the location of user's eyes were also reduced about 2 [mm] per target, which was a half of that before the calibration. This result was well enough to prove the effectiveness of the calibration methods.

An Online Calibration Method for Microsoft HoloLens

“…It is not practical to capture images as seen by the eye, therefore, the correspondences between points in the real world, points in the HMD display, and locations on the retina cannot be directly measured. Since it is unable to capture the images as seen by eyes, OST-HMDs, are difficult to calibrate [19] In 1994, Oishi and Tachi [20] proposed a shooting-gallery method, in which the head of the user was fixed on a chin rest and the user aimed at targets that were shown at varying distances. Azuma [17] used a bore-sight method in which a crosshair pattern must be aligned with the physical line of sight.…”