How I created an API to correct GPS to Sea Level.

A simple solution to a complicated problem.

Photo by Cristina Gottardi on Unsplash

The Problem

GPS is wonderful!

But it has problems with altitude!

Very simply:

• Vertical GPS measurements are just less accurate (because of geometry), and
• We don’t know where the surface of the Earth is!

Putting aside the first (since fixing geometry is beyond the scope of the article :), this article documents how to create a solution for “finding the surface of the Earth” or more accurately how to convert from GPS coordinates to a height above Mean Sea Level (MSL) which is defined for the purpose of this API as the WGS84 Orthometric Height.

What is GPS’ problem with altitudes?

I previously investigated the problems analysing and using GPS altitudes, especially on smartphones and other small devices, in this article:

How to draw a gradient profile using GPS track data and polynomials

NOTE — throughout this article I will talk about GPS. I should actually be…