Expectation Maximization to Determine Position of Ambient Glints

A system comprising:

• a non-transitory computer-readable medium;
• and
• program instructions stored on the non-transitory computer-readable medium and executable by at least one processor to:
• (a) analyze eye-image data to determine observed movement of an ambient glint on an eye surface;
• (b) determine an expected movement of the ambient glint on the eye surface given a value of a z-distance parameter;
• (c) determine a difference between the observed movement of the ambient glint on the eye surface and the expected movement of the ambient glint on the eye surface;
• (d) if the difference is less than a threshold, then associate the value of the z-distance parameter with a source of the ambient glint;
• and
• (e) if the difference is greater than the threshold, then:
• (i) make a predetermined adjustment to the value of the z-distance parameter;
• and
• (ii) repeat (a) to (d) with the adjusted value of the z-distance parameter.

A non-transitory computer readable medium having stored therein instructions executable by a computing device to cause the computing device to perform functions comprising:

• (a) analyzing eye-image data to determine observed movement of a reflected feature on an eye surface;
• (b) determining an expected movement of the reflected feature on the eye surface given a value of a z-distance parameter;
• (c) determining a difference between the observed movement of the reflected feature on the eye surface and the expected movement of the reflected feature on the eye surface;
• (d) if the difference is less than a threshold, then associating the value of the z-distance parameter with a source of the reflected feature;
• and
• (e) if the difference is greater than the threshold, then:
• (i) making a predetermined adjustment to the value of the z-distance parameter;
• and
• (ii) repeating (a) to (d) with the adjusted value of the z-distance parameter.