A computer-implemented method comprising: accessing , by a computer system, position data of a first virtual reality head-mounted display, the position data generated based on image data of a physical environment that comprises the first virtual reality head-mounted display, the image data generated by an optical sensor of a second virtual reality head-mounted display; determining , by the computer system, a position of the first virtual reality head-mounted display in the physical environment based on the position data; and causing , by the computer system, a presentation of virtual reality content at the first virtual reality head-mounted display based on the position in the physical environment, wherein the first virtual reality head-mounted display comprises the computer system, wherein accessing the position data comprises receiving the position data from the second virtual reality head-mounted display over a peer-to-peer data communication network, and wherein the position of the first reality head-mounted display is tracked over time based on updates to the position data, wherein the position data is further generated based on first inertial data of the first virtual reality head-mounted display and based on second inertial data of the second virtual reality head-mounted display, wherein the first inertial data is generated by a first inertial measurement unit rigidly connected with the first virtual reality head-mounted display, and wherein the second inertial data is generated by a second inertial measurement unit rigidly connected with the second virtual reality head-mounted display. accessing , by a computer system, position data of a first virtual reality head-mounted display, the position data generated based on image data of a physical environment that comprises the first virtual reality head-mounted display, the image data generated by an optical sensor of a second virtual reality head-mounted display; determining , by the computer system, a position of the first virtual reality head-mounted display in the physical environment based on the position data; and causing , by the computer system, a presentation of virtual reality content at the first virtual reality head-mounted display based on the position in the physical environment, wherein the first virtual reality head-mounted display comprises the computer system, wherein accessing the position data comprises receiving the position data from the second virtual reality head-mounted display over a peer-to-peer data communication network, and wherein the position of the first reality head-mounted display is tracked over time based on updates to the position data, wherein the position data is further generated based on first inertial data of the first virtual reality head-mounted display and based on second inertial data of the second virtual reality head-mounted display, wherein the first inertial data is generated by a first inertial measurement unit rigidly connected with the first virtual reality head-mounted display, and wherein the second inertial data is generated by a second inertial measurement unit rigidly connected with the second virtual reality head-mounted display. <EOS>