Rapid target acquisition using gravity and north vectors

A computer system configured to align images generated by two cameras, where the alignment is performed by computing a relative three-dimensional (3D) orientation between the two cameras, said computer system comprising:

• one or more processors;
• and
• one or more computer-readable hardware storage devices that store instructions that are executable by the one or more processors to cause the computer system to:
• determine a first gravity vector for a first camera;
• determine a second gravity vector for a second camera that is physically detached from the first camera;
• obtain a first camera image from the first camera and a second camera image from the second camera, wherein the first camera had a first orientation when the first camera image was generated and the second camera had a second orientation when the second camera image was generated;
• perform a first alignment process to partially align the first orientation with the second orientation by aligning the first gravity vector with the second gravity vector, thereby resulting in two degrees of freedom of the relative 3D orientation being eliminated;
• identify visual correspondences between the first camera image and the second camera image;
• perform a second alignment process to fully align the first orientation with the second orientation by using the identified visual correspondences to identify and eliminate a third degree of freedom of the relative 3D orientation;
• and
• subsequent to performing the first alignment process and the second alignment process, generate an overlaid image by overlaying content included in one of the first camera image or the second camera image onto corresponding content included in the other one of the first camera image or the second camera image.

A head-mounted device (HMD) configured to align images generated by two cameras, where the alignment is performed by computing a relative three-dimensional (3D) orientation between the two cameras, said HMD comprising:

• an HMD camera;
• one or more processors;
• and
• one or more computer-readable hardware storage devices that store instructions that are executable by the one or more processors to cause the computer system to:
• determine a first gravity vector for the HMD camera;
• determine a second gravity vector for a second camera that is physically detached from the HMD camera;
• obtain a first camera image from the HMD camera and a second camera image from the second camera, wherein the HMD camera had a first orientation when the first camera image was generated and the second camera had a second orientation when the second camera image was generated;
• perform a first alignment process to partially align the first orientation with the second orientation by aligning the first gravity vector with the second gravity vector, thereby resulting in two degrees of freedom of the relative 3D orientation being eliminated;
• identify visual correspondences between the first camera image and the second camera image;
• perform a second alignment process to fully align the first orientation with the second orientation by using the identified visual correspondences to identify and eliminate a third degree of freedom of the relative 3D orientation;
• and
• subsequent to performing the first alignment process and the second alignment process, generate an overlaid image by overlaying content included in one of the first camera image or the second camera image onto corresponding content included in the other one of the first camera image or the second camera image.