One set solves the direct problem: given one point on the Earth's surface (latitude and longitude), a direction, and a distance, these equations find the latitude and longitude of the ending point. Th...One set solves the direct problem: given one point on the Earth's surface (latitude and longitude), a direction, and a distance, these equations find the latitude and longitude of the ending point. The other set solves the inverse problem: given two points on the Earth's surface (latitudes and longitudes), these equations find the distance between the two points, as well as the direction from one point the other.