I am impostor here, and am by no means mathematically literate, so please bare with me.
I have posted a software question on StackOverflow, regarding an unexpected drift in latitude using Vincenty's Direct formula; https://stackoverflow.com/questions/31687723/vincenty-direct-formula-latitude-issue
I am trying to calculate a new location when travelling due east from a known location and distance.
What has surprised me is when calculating using a 90 degree bearing, the Latitude drifts south.
This is not the case at the equator, but certainly is closer to the pole.
Can anyone explain this effect? Are there any other formulas I could use in place of Vincenty direct to avoid this drift?