The inverse geodesic problem is: given two points, determine the forward and back azimuths and the distance.

The inverse geodesic problem is: given two points, determine the forward and back azimuths and the distance.

• A. Direct problem
• B. Convergence problem
• C. Projection problem
• D. Inverse problem

Answer: (D)

To understand this, focus on what you’re given and what you’re solving for. You have two known points and you want the path parameters that connect them: the initial bearing from the first point toward the second, the bearing in the opposite direction from the second back toward the first, and the distance along the reference ellipsoid between them. Those three values—two azimuths and the distance—define the geodesic when both endpoints are known, which is exactly the inverse geodesic problem. The direct problem is the opposite: you start from a point, specify an initial direction, and a distance, then compute where you end up. The other terms don’t describe this task. The distance here is the ellipsoidal geodesic distance, and the azimuths are the directions along the surface at the endpoints.

To understand this, focus on what you’re given and what you’re solving for. You have two known points and you want the path parameters that connect them: the initial bearing from the first point toward the second, the bearing in the opposite direction from the second back toward the first, and the distance along the reference ellipsoid between them. Those three values—two azimuths and the distance—define the geodesic when both endpoints are known, which is exactly the inverse geodesic problem.

The direct problem is the opposite: you start from a point, specify an initial direction, and a distance, then compute where you end up. The other terms don’t describe this task. The distance here is the ellipsoidal geodesic distance, and the azimuths are the directions along the surface at the endpoints.