Solid angle The solid angle subtended by a surface S is defined as the surface area of a unit sphere covered by the surface S's projection onto the sphere. A solid angle is related to the surface of a sphere in the same way an ordinary angle is related to the circumference of a circle. Since the total surface area of the unit sphere is 4*pi, the measure of solid angle will always be between 0 and 4*pi. Space and Time QUDT http://qudt.org/vocab/quantity#Solidangle ODM2 Units Type Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of the Unit or the more general quantity that the Unit represents.