Geodesy-PHP is a port of some known geodesic/math functions for getting distance from a known point A to a known point B given their coordinates (good for working out distances between different latitude/longitude data provided by Google Geolocation or any RESTful APIs).

It also supports conversion between units of length, Polar position to Cartesian coordinates, and different Reference Datums.

It provides distance calculations by:

1. Spherical Law of Cosines

2. Haversine Formula

1. Vincenty's Formula

2. Hubeny's Formula

3. Thomas' Formula

4. Andoyer-Lambert Formula

5. Elliptic Distance

6. Forsythe-Andoyer-Lambert Formula

All operations are set in Metre. But it can also convert distance (and other transformation) values to:

1. Kilometre

2. Mile

3. Nautical Mile

4. Astronomical Unit

It also allows coordinate/geographical conversions between the ff:

1. Polar to Cartesian

2. Cartesian to Polar

3. Polar to Web Mercator

4. Web Mercator to Polar

Reference Datums are and will be, by default, set to WGS84. You can also transform one coordinate taken from a different source to another (see this for reference), as it also comes with pre-built datums (see the Datum namespace for options).

The following are the transformation options:

1. 3-Parameter Molodensky Transformation

2. 7-Parameter Helmert Transformation

3. 10-Parameter Molodensky-Badekas Transformation

You can read about it here