Note 1 to entry: Since ∫ 0 2π D( θ,f )dθ=1 MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGeaGqipG0dh9qqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9ad baGaciGabaqaamaaceGaaiGacaabaaGcbaWaa8qCaKaaafaacaWGebGcdaqadaqcaauaaiaajI7acaGGSaGaamOzaaGaayjkaiaawMcaaiaabsgacaqI4oGaeyypa0JaaeymaaqcbauaaiaaicdaaeaacaqGYaGaaqiWdaqcdaKaey4kIipaaaa@425D@ the directional spreading function can be considered to be a probability density function over direction.