Great circle trajectories around a sphere

What’s the best way to calculate great circle trajectories, knowing the velocity (tangent to sphere) of an orbiting object?

just draw a straight line (ie through the planet)

simply raise that to be a tangent to the surface

(go away from the center of the sphere until 90 away)

Hey Ina - do you need more than this? This is exactly how you do it. It’s remarkably easy in Unity.

It was a lot harder for navigators in the 1800s! :slight_smile:


You further wanted to know how to do this using built-in functions.

direct line = B - A

(use the built-in subtraction of Vector3)

AToCenter = planetCenter - A
temp = direct line X AToCenter
final result = AToCenter X temp

the large “X” represents Cross Product which is an operation between Vectors. Cross Product is built-in to Unity: