These images of en plein air paintings done in Rome (in roughly two hours) illustrate the emulator’s task of representation (what one sees) combined with a deference to a tradition (how one sees). The modern notion of realism puts a high value on direct observation, but seemingly ignores the tradition of how others have observed the same subjects. If one emulates in the classical tradition when working en plein air, one is conscious of the tradition of plein air painting even in the choice of subject. Composition of subject, in other words, is just as important as technique.
FYI, the Columns of the Temple of Apollo next to the Theater of Marcellus in Rome owe a debt to Panini, while the Urn from the courtyard at Sta. Cecilia was a subject of Piranesi.
More en plein air work can be seen at davidmayernik.com