Flat Earthers admit defeat after Antarctica trip proves them wrong

I think it can be done with far less travel. One can observe the length of a shadow of an object with a known height at solar noon for a year. Then travel north by car for half a day and observe the length of shadow. Then travel south by car for half a day and observe the length. You can actually use these measurements not only to demonstrate that you aren’t on a flat plane, but also to estimate the radius of the earth.