Alignment Issues for any Sample Direction BTF Measurement

Measurement of the bidirectional texture function (BTF) of the surfaces with portable instruments allowing on-site measurement outside the laboratory conditions is a newly emerging technique enabling data acquisition of the real objects without the necessity of their extraction from the environment. A practical issue of the sample measurement is the instrument alignment regarding the measured surface. The aim is to measure a sample surface under any orientation in space and to align the measurement instrument to the surface so to measure surface reflectance of the sample surface. This paper describes the design of two setups allowing adjustment of a portable BTF measurement instrument regarding the sample surface at any position. The final instrument alignment is performed with a help of feedback information provided by a simple laser autocollimator.