When grading an exam, I discovered that QGIS 3.2 and 3.4 produce different values on computing
$area over polygons.
I experimented using
area($geometry) to check the differences between planar and ellipsoid computations. It seems that QGIS 2.18 computes planar areas as default for
$area, whereas QGIS 3.4 gives ellipsoidal areas for
$area (as explained at the help section of the function).
In QGIS 3.2,
$area produces different values (quite higher) than those for
$area in QGIS 3.4, whereas
area($geometry) produces the same values in the two versions.
As context, my data is projected on EPSG:32717 (WGS84 UTM z17 S).
Any insights on what's going on? Is this a bug? I'd like to explain the students these caveats and to be aware when computing area-derived variables.