An apparatus comprising: a sensor and a logic configured to monitor orientation of a person's head using the sensor, including monitoring rotation about an axis of the head, including determining a present Euler angle with respect to rotation about the axis of the head, and including recording the present Euler angle such that Euler angles are recorded over a time period; wherein the logic is configured to determine a three-dimensional ray based on the present Euler angle such that the 3D ray has a motion that tracks the present Euler angle over time, wherein the 3D ray is a first 3D vector that originates from the head, and the 3D ray extends outward in a direction in which the person is looking such that the direction of the 3D ray is determined entirely on the orientation of the person's head by tracking the present Euler angle over time; wherein the logic is configured to determine a mathematical variance of the recorded Euler angles by comparing the present Euler angle with the Euler angles recorded over the time period, wherein the logic is configured to generate an interaction ray, wherein the origin of the interaction ray is the same as the origin of the three-dimensional ray, and the direction of the interaction ray is such that the interaction ray tracks the direction of the three-dimensional ray to such an extent that the closeness of tracking is proportional to the mathematical variance of the recorded Euler angles, wherein the logic is configured to present a virtual image in a head mounted display, the virtual image comprising 3D virtual objects, and wherein the logic is configured to determine a collision of the interaction ray with a first 3D virtual object of the 3D virtual objects at a 3D coordinate, such that the interaction ray is used as a selector or pointer. a sensor and a logic configured to monitor orientation of a person's head using the sensor, including monitoring rotation about an axis of the head, including determining a present Euler angle with respect to rotation about the axis of the head, and including recording the present Euler angle such that Euler angles are recorded over a time period; wherein the logic is configured to determine a three-dimensional ray based on the present Euler angle such that the 3D ray has a motion that tracks the present Euler angle over time, wherein the 3D ray is a first 3D vector that originates from the head, and the 3D ray extends outward in a direction in which the person is looking such that the direction of the 3D ray is determined entirely on the orientation of the person's head by tracking the present Euler angle over time; wherein the logic is configured to determine a mathematical variance of the recorded Euler angles by comparing the present Euler angle with the Euler angles recorded over the time period, wherein the logic is configured to generate an interaction ray, wherein the origin of the interaction ray is the same as the origin of the three-dimensional ray, and the direction of the interaction ray is such that the interaction ray tracks the direction of the three-dimensional ray to such an extent that the closeness of tracking is proportional to the mathematical variance of the recorded Euler angles, wherein the logic is configured to present a virtual image in a head mounted display, the virtual image comprising 3D virtual objects, and wherein the logic is configured to determine a collision of the interaction ray with a first 3D virtual object of the 3D virtual objects at a 3D coordinate, such that the interaction ray is used as a selector or pointer.