Wearable video headset and method for calibration
During calibration, a wearable video headset displays a pattern on a partially transparent display positioned in a field of view of a user's eye. The user has a hand-held marker that includes a scaled version of the displayed pattern. The user moves the marker toward or away from the user's eye until the pattern on the marker appears to be the same size as the pattern on the display. When the sizes match, the headset measures a distance between a forward-facing camera and the hand-held marker. The headset uses the measured distance, and geometrical relationships, to determine the spacing between the user's eye and the display. Such calibration can ensure that the images displayed to the user mesh realistically with the surroundings, which remain partially visible through the partially transparent display of the video headset.
1. A method for calibrating a video headset worn on a head of a user, the method comprising:
displaying a pattern on a display of the video headset, the display being at least partially transparent and positioned in a field of view of an eye of the user;
determining that a marker including a scaled version of the pattern is positioned in the field of view of the eye at a first longitudinal position away from the video headset, such that when the marker is positioned at the first longitudinal position, the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
when the marker is positioned at the first longitudinal position, measuring a distance between a forward-facing camera on the video headset and the marker; and
calculating, with a processor, a spacing between the eye and the display, based in part on the measured distance;
wherein calculating the spacing between the eye and the display comprises:
receiving the measured distance between the forward-facing camera and the marker; and
calculating, with the processor, the spacing between the eye and the display, based in part on the received measured distance, and using an expression based on a linear increase of the field of view of the eye, as a function of longitudinal distance, from a fovea of the eye;
wherein:
the expression comprises
ID
=
(
DC
+
CM
)
(
1
XMARK
XDISP
-
1
)
-
FI
;
FI is a longitudinal spacing between the fovea of the eye and an iris of the eye;
ID is a longitudinal spacing between the iris of the eye and the display;
DC is a longitudinal spacing between the display and the forward-facing camera;
CM is the received measured distance, corresponding to a measured longitudinal spacing between the forward-facing camera and the marker when the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
XMARK is a relative size of the pattern on the marker along one lateral dimension; and
XDISP is a relative size of the pattern on the display along the same lateral dimension.
2. The method of claim 1 , wherein spacing FI is selected to equal 24 mm, which corresponds to an average diameter of a human eyeball.
3. The method of claim 1 , wherein spacing CM is selected to be less than 635 mm, whereby 635 mm corresponds to an average human arm length.
4. The method of claim 1 , wherein determining that the marker is positioned at a first longitudinal position comprises:
automatically sensing with the forward-facing camera that the pattern on the marker in the field of view of the eye is sized to match the pattern on the display in the field of view of the eye to within a specified threshold.
5. The method of claim 1 , wherein determining that the marker is positioned at a first longitudinal position comprises:
receiving notification from the user that the user perceives the marker in the field of view of the eye to have the same size as the pattern on the display in the field of view of the eye.
6. The method of claim 1 , wherein the pattern is a two-dimensional pattern on a surface normal to an axis along the field of view of the eye.
7. The method of claim 6 , wherein the pattern includes at least one two-dimensional fiducial marker.
8. The method of claim 1 , further comprising:
generating, using the processor, augmented reality content based on video data from the forward-facing camera on the video headset; and
displaying the augmented reality content in the display based on the spacing between the eye and the display, the augmented reality content perceived at a predefined focal point based on the spacing between the eye and the display.
9. The method of claim 1 , further comprising:
receiving augmented reality content from a server based on video data from the forward-facing camera on the video headset; and
displaying the augmented reality content in the display based on the spacing between the eye and the display, the augmented reality content perceived at a predefined focal point based on the spacing between the eye and the display.
10. A video headset wearable on a head of a user, comprising:
a display being at least partially transparent and positioned in a field of view of an eye of the user;
a processor; and
memory including instructions that, when executed on the processor, cause the processor to perform operations, the operations comprising:
displaying a pattern on the display;
determining that a marker including a scaled version of the pattern is positioned in the field of view of the eye at a first longitudinal position away from the video headset, such that when the marker is positioned at the first longitudinal position, the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
when the marker is positioned at the first longitudinal position, measuring a distance between a forward-facing camera on the video headset and the marker; and
calculating, with the processor, a spacing between the eye and the display, based in part on the measured distance;
wherein calculating the spacing between the eye and the display comprises:
receiving the measured distance between the forward-facing camera and the marker; and
calculating, with the processor, the spacing between the eye and the display, based in part on the received measured distance, and using an expression based on a linear increase of the field of view of the eye, as a function of longitudinal distance, from a fovea of the eye;
wherein:
the expression comprises
ID
=
(
DC
+
CM
)
(
1
XMARK
XDISP
-
1
)
-
FI
;
FI is a longitudinal spacing between the fovea of the eye and an iris of the eye;
ID is a longitudinal spacing between the iris of the eye and the display;
DC is a longitudinal spacing between the display and the forward-facing camera;
CM is the received measured distance, corresponding to a measured longitudinal spacing between the forward-facing camera and the marker when the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
XMARK is a relative size of the pattern on the marker along one lateral dimension; and
XDISP is a relative size of the pattern on the display along the same lateral dimension.
11. The video headset of claim 10 , wherein:
spacing FI is selected to equal 24 mm, which corresponds to an average diameter of a human eyeball; and
spacing CM is selected to be less than 635 mm, whereby 635 mm corresponds to an average human arm length.
12. The video headset of claim 10 , wherein determining that the marker is positioned at a first longitudinal position comprises:
automatically sensing with the forward-facing camera that the pattern on the marker in the field of view of the eye is sized to match the pattern on the display in the field of view of the eye to within a specified threshold.
13. The video headset of claim 10 , wherein determining that the marker is positioned at a first longitudinal position comprises:
receiving notification from the user that the user perceives the marker in the field of view of the eye to have the same size as the pattern on the display in the field of view of the eye.
14. The video headset of claim 10 , wherein the pattern includes at least one two-dimensional fiducial marker.
15. A method for calibrating a video headset worn on a head of a user, the method comprising:
displaying a pattern on a display of the video headset, the display being at least partially transparent and positioned in a field of view of an eye of the user;
determining that a marker including a scaled version of the pattern is positioned in the field of view of the eye at a first longitudinal position away from the video headset, such that when the marker is positioned at the first longitudinal position, the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
when the marker is positioned at the first longitudinal position, measuring a distance between a forward-facing camera on the video headset and the marker; and
calculating, with a processor, a spacing between the eye and the display, based in part on an expression comprising
ID
=
(
DC
+
CM
)
(
1
XMARK
XDISP
-
1
)
-
FI
;
wherein:
FI is a longitudinal spacing between the fovea of the eye and an iris of the eye;
ID is a longitudinal spacing between the iris of the eye and the display;
DC is a longitudinal spacing between the display and the forward-facing camera;
CM is the received measured distance, corresponding to a measured longitudinal spacing between the forward-facing camera and the marker when the pattern on the marker appears to be the same size as the pattern on the display in the field of view of the eye;
XMARK is a relative size of the pattern on the marker along one lateral dimension; and
XDISP is a relative size of the pattern on the display along the same lateral dimension.
16. The method of claim 15 , wherein:
spacing FI is selected to equal 24 mm, which corresponds to an average diameter of a human eyeball; and
spacing CM is selected to be less than 635 mm, whereby 635 mm corresponds to an average human arm length.