I have an image of a map and a point marked onto it. I have those coordinates (as a percentage) inside the image of the point. Now I'd like to know the coordinate (latitude/longitude) that this point would have.
For better understanding what I mean I made a little scribble inside a map. To my point for example is at 10% East and 30% North. Getting the longitude is easy as I just need to take 10% of 180° and I have my 18° East. Great. But as the latitude is a projected ellipsoid it's not that easy any more.
I found an other question here that pointed to this e-book here: https://pubs.usgs.gov/pp/1395/report.pdf On page 44 there should be the explanation and on page 267 a sample, but I just can't find the correct coordinates using that equation.
I would be super happy if anybody could give me pseudo code or something on how to calculate a lat/lng coordinate from my percentage coordinates.