EDIT: I was playing around with this sandcastle
Find the intersection point of a polyline with a circle / sphere
and discovered that interpolate can also extrapolate! So now I guess the next big thing would be determining the 2 intersection points of 2 great circles.
I suppose the main functionality that I don’t see is geodesic extrapolation, just interpolation. I tried using the interpolation method for extrapolation, but it didn’t seem to work, perhaps I didn’t use it correctly. Great Circles simply being geodesics that go all the way around, so just expanding the geodesic library would be nice. I think drawing geometry along the curve of the Earth is in another library, possibly by web workers?
Meridians and the Equator are easy as all points are on the same longitude (latitude for Equator.) However other Great Circles aren’t so easy to calculate, why extrapolation would be useful.
Unlike Rhumblines Great circles are straight lines on a globe (equator and meridians being exceptions, as they are both Rhumblines and Great Circles), representing the shortest path between two points. Very useful for Aircraft and ship navigation. Say a geodesic only went so far, and you wanted to extend it. How would you identify points in the distance to target to extent it?
Wondering where the paths of 2 crafts intersect, Great Circle intersection could assist (then see when they’d arrive at that point.)
EDIT: no need after finding out that interpolate can indeed also extrapolate.
Spherical geocentric math is fairly easy, but ellipsoidal math is a bit tricky. I suppose I could transcribe the extrapolation code I linked to to Cesium, I could then make a Sandcastle example to demonstrate it.
EDIT2: some related recent posts
Finding a point on the surface at a given distance
Move a Cartographic by a distance in meters?