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Target apparatus and method of making a measurement with the target apparatus

  • US 8,467,072 B2
  • Filed: 02/29/2012
  • Issued: 06/18/2013
  • Est. Priority Date: 02/14/2011
  • Status: Active Grant
First Claim
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1. A method comprising steps:

  • providing the target, wherein the target has a target frame of reference and includes a first retroreflector and a body, the body having a spherical exterior portion that has a sphere center and a sphere radius, the body containing a cavity, the cavity sized to hold the first retroreflector, the cavity open to the exterior of the body, the first retroreflector at least partially disposed in the cavity, the first retroreflector having a first retroreflector reference point in the target frame of reference;

    providing the device, wherein the device has a device frame of reference and a first light source, the device being configured to measure a distance and two angles from the device to the first retroreflector reference point;

    determining at least one vector length component in the target frame of reference of a vector that extends from the first retroreflector reference point to the sphere center, the vector having a length greater than zero;

    illuminating the first retroreflector with light from the first light source to provide a first reflected light that is returned to the device;

    measuring, from the device to the first retroreflector reference point, a first distance and a first set of two angles based at least in part on the first reflected light, the first distance based at least in part on a speed of light over a path traveled by the light from the device to the first retroreflector reference point;

    determining three orientational degrees of freedom of the target frame of reference in the device frame of reference, wherein the three orientational degrees of freedom are sufficient to fully define the orientation of the target frame of reference in the device frame of reference;

    calculating three dimensional coordinates of the sphere center within the device frame of reference based at least in part on the first distance, the first set of two angles, the three orientational degrees of freedom, and the at least one vector length component; and

    storing the three dimensional coordinates of the sphere center;

    in the step of providing the target, the first retroreflector is selected to be a cube corner retroreflector having three planar reflectors, each planar reflector capable of reflecting light, each planar reflector perpendicular to the other two planar reflectors, each planar reflector intersecting the other two planar reflectors in a common vertex, and each planar reflector having two intersection junctions, each intersection junction shared with an adjacent planar reflector for a total of three intersection junctions within the cube corner retroreflector, the cube corner retroreflector having an axis of symmetry relative to the three planar reflectors; and

    in the step of determining at least one vector length component, the first retroreflector reference point is the vertex.

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