Calculate the distance between two sets of coordinates in WGS84

When error checking, it can be very useful to measure a distance between two WGS84 points. For example, we use this tool to verify that our PPK processing for ground control points is giving us the results we expect.

The distance is calculated as a Great Circle measurement, although for error checking small discrepancies this is effectively the same as a direct distance measurement.

Coordinates should be separated by spaces, with an optional ellipsoid height specified.