Specularities on surfaces with tangential hairs or grooves

Specularities on surfaces with tangential hairs or grooves are readily obse rvable in nature. Examples of such phenomena are the arched or looped highl ights observed on horses and human heads and the linear or curved speculari ties observed on parts of industrial machinery that have tangential grooves . We investigate the geometry of curvilinear specularities on surfaces of d ifferent curvature with tangential hairs or grooves of different orientatio ns under controlled lighting and viewing conditions. First the nature of th ese specularities is investigated qualitatively. Then specularities on para metric surfaces and hair or groove orientations are calculated for some spe cific cases. Explicit calculations of specularities on some special surface s, cylinders, cones, and spheres, are verified by photographs of the reflec tions. Aspects of the work are applicable to computer graphics and can be u tilized for the image interpretation of surface specularities. (C) 2000 Aca demic Press.