Copy CSV data in first text field and click Process. In the second field there will be the data displayed in cartesian coordinates, x in the south meriadian direction, y in the east direction. The coordinates are in meters. The radius of the flat earth is 20,015,086.796 m.

I can output the data in other formats if you want. Or change the plot as you like.

You can calculate the distance of a point from the center of the FE either with Pythagoras from the xy coordinates or as r = (90 − latitude) / 180 · π · R, where R = 6371 km is the radius of the earth.

CSV Data: date, latitude, longitude

CSV Flat Earth Data: date, X, Y

Flat Earth Plot

First data point is plotted with a big marker.