When I create a circular buffer around a point feature in QGIS 3.36.3-Maidenhead in EPSG:25832 of a 10 km radius with 1000 segments I get 313961275.193 m² as a result. I calculate the area by typing $area into the field calculator. But when I calculate it by using
Pi * r^2 = A
i get 314159265.359 m² as the area.
The buffer prompt:
Where does the difference come from?
area($geometry), hence your measurements take the ellipsoid into account.area($geometry), but that does not give me analytical result either (as every thing else is just 1, its basically the numbers of Pi and only the position of the punkt changes. I added a screenshot of the buffer prompt so you can tell how i calculated the buffer.