Geography utils

For folks looking for general geography utils, i.e. the stuff that is available in most languages through packages like GDAL, I've recently open-sourced a small amount of code in the form of a library: https://github.com/bostonrwalker/navutils/blob/main/source/navutils.mc

Collaborators are welcome!

Calculate initial bearing with 

• θ = atan2( sin Δλ ⋅ cos φ2 , cos φ1 ⋅ sin φ2 − sin φ1 ⋅ cos φ2 ⋅ cos Δλ )

Where:

• θ is the initial bearing (in radians).
• φ1 is the latitude of the starting point.
• φ2 is the latitude of the destination point.
• λ1 is the longitude of the starting point.
• λ2 is the longitude of the destination point.
• Δλ is the difference in longitude (λ2 - λ1).

dxt = asin( sin(δ13) ⋅ sin(θ13−θ12) ) ⋅ R

• Where:
  • dxt is the cross-track distance. 
  • δ13 is the angular distance from the start point to the third point (the point in question).
  • θ13 is the initial bearing from the start point to the third point.
  • θ12 is the initial bearing from the start point to the end point of the segment.
  • R is the Earth's radius.

If you’ve got the Haversine distance, divide by the Earths radius to get angular distance.

All in radians.