In QGIS, I often find myself setting up projects with an ellipsoid coordinate system (e.g. WGS84) so that the resulting maps have lat lon scales, etc.
Often in these projects I also need to do some calculations in other units (e.g. calculate the sq km of a feature).
At present I do this my maintaining two versions of a shapefile, one projected for calculations and one ellipsoid for layouts.
This becomes complicated in large projects!
Is there an easier way? Am I overlooking a technique for doing these calculations on-the-fly from spheroid shapefiles?