Don't my references to bendy light, elephants, turtles, and how you explain the sun INDICATE that I have already?
how would you explain gps? i code gps for a living, and if the earth were flat the data we hold of the satellites' positions would be significantly off. triangulation would fail, and gps would not be able to pinpoint your location as accurately as it does. It follows the same logic as the following:
suppose a tower were built to be a fixed (large) height above the earths surface. if the tower sent signals to various locations around the world, it would take x amount of time to reach those locations. due to the "hypothetical curvature" of the earth in this scenario, the time it takes to reach those locations would be significantly off, and actually the dimensions of the earth could be calculated with this experiment. although this particular instance hasnt been instantiated, there is no need for it to be because the same scenario occurs with satellites, triangulation and gps.