I'm working on a system that transform data from Long/Lat/Alt (WGS84) to a local tangent plane (LTP) East/North/Up coordinate system. To go from WGS84 to LTP, the coordinates first need to be transformed to Earth-Centered Earth-Fixed (ECEF) coordinates and then translated and rotated.

I was quite surprised to find that while it is straightforward to go from WGS84 to ECEF with a closed form, the other way, from ECEF to WGS84, needs to be computed iteratively [1] and is not trivial to find.

[1] https://en.wikipedia.org/wiki/Geographic_coordinate_conversi...