Before revision: That is, if the initial orthodromic course θ from the starting point S to the fixed point X is 80 degrees, the associated isoazimuth is formed by all points whose initial orthodromic course with respect to point X is 80° .
After revision: (with respect to true north)That is, if the initial orthodromic course θ from the starting point S to the fixed point X is 80 degrees, the associated isoazimuth is formed by all points whose initial orthodromic course with respect to point X is 80° .