Building a gonioreflectometer - a geometrical evaluation

A gonioreflectometer is a device for measuring the reflectance properties of the surface of a specimen by means of the bidirectional reflectance distribution function (BRDF). In order to scan the 4D BRDF parameter space, such a device requires at least one light source and one detector and the ability to move at least two of the following: light source, detector, and specimen. In this work we analyze the geometry of a conceptual measurement device where the specimen is moved by three rotary stages assembled to form a gimbal mount. The camera - as detector - remains fixed, and the light source is moved along a circular trajectory centered on the specimen surface. The model presented allows evaluation of the subspace of the BRDF parameter space that is accessible using a given measurement setup.