The Dimensional Metrology Group (683.01) provides special tests for instruments that measure distance using the passive reflectance of the target, i.e., non-cooperative targets. This includes various types of laser scanner measuring systems frequently used in land surveying, reverse engineering and large scale manufacturing.
The ranging capability of these instruments can be testing using either planar or spherical targets. The facility currently uses titanium spheres with a matte surface arranged at regular intervals of 5 meters along a line approximately 65 meters in length, with 8 extra spheres at various locations along the line. Each sphere is nominally 4 inches in diameter and is calibrated for size, form, and relative distance to each of the other spheres. Alternatively, planar targets up to 150 mm square can be used on a displaceable rail system. Special fixtures allow the NIST system to determine the absolute distance to a measurement point on a non-cooperative target.
Each calibration includes a NIST calibration report that provides the error in the distance for each test performed. The user may specify the number and length of each absolute distance test up to a maximum length of 65 meters.
The expanded uncertainty U with k = 2 in the sphere-to-sphere center distance U (k = 2) = (22 + 0.6L) µm where L is the length of the interval in meters.