Electromagnetic tracking of objects for mixed reality

A method of locating an object in a mixed reality system, the method comprising:

• determining a location of a location sensor of a head-mounted display (HMD) device in space;
• emitting an electromagnetic field from a base station mounted at a fixed position relative to the HMD device a predetermined offset from the location sensor;
• sensing a strength of the electromagnetic field with an electromagnetic field sensor affixed to the object;
• determining, with a processor of the HMD device, a location of the electromagnetic field sensor relative to the base station based on the sensed strength;
• and
• determining, with the processor, a location of the electromagnetic field sensor in space based on the relative location, the predetermined offset, and the location of the location sensor in space.

A mixed reality system comprising:

• an electromagnetic field sensor affixed to an object and configured to sense a strength of an electromagnetic field;
• and
• a head-mounted display (HMD) device comprising:
• a location sensor from which the HMD device determines a location of the location sensor in space;
• a base station mounted at a fixed position relative to the HMD device a predetermined offset from the location sensor and configured to emit the electromagnetic field;
• a processor configured to:
• determine a location of the electromagnetic field sensor relative to the base station based on the sensed strength;
• and
• determine a location of the electromagnetic field sensor in space based on the relative location, the predetermined offset, and the location of the location sensor in space;
• and
• an at least partially see-through display configured to display augmented reality images and overlay a hologram that corresponds to the location of the electromagnetic field sensor in space over time.