12-05-2016, 08:29 AM

The direct geodesy problem: given Lat Lon distance and bearing find Lat Lon 2.

The inverse: Given two points find the distance.

All the references I have seen, such as Wikipedia, start by giving a spherical solution for the inverse problem, then progress to the Vincenty inverse and direct solutions for ellipsoidal accuracy.

I'm curious - perhaps someone can explain...

Does this mean that the direct solution was not solvable until Vincenty? As far as on-line references go, there is no mention of how it was solved.

Or is it meant to be blindingly obvious that you can just run the spherical code in reverse...surely if it can be done, someone would have implemented it?

The reason I am so interested...

I have attempted an implementation of the Vincenty direct formula, but it is not correct - so I was looking for a way of generating some test data for comparison.

The inverse: Given two points find the distance.

All the references I have seen, such as Wikipedia, start by giving a spherical solution for the inverse problem, then progress to the Vincenty inverse and direct solutions for ellipsoidal accuracy.

I'm curious - perhaps someone can explain...

Does this mean that the direct solution was not solvable until Vincenty? As far as on-line references go, there is no mention of how it was solved.

Or is it meant to be blindingly obvious that you can just run the spherical code in reverse...surely if it can be done, someone would have implemented it?

The reason I am so interested...

I have attempted an implementation of the Vincenty direct formula, but it is not correct - so I was looking for a way of generating some test data for comparison.