  With the aim of paving the road for future accurate astrometry with MICADO at
the European-ELT, we performed an astrometric study using two different but
complementary approaches to investigate two critical components that contribute
to the total astrometric accuracy. First, we tested the predicted improvement
in the astrometric measurements with the use of an atmospheric dispersion
corrector (ADC) by simulating realistic images of a crowded Galactic globular
cluster. We found that the positional measurement accuracy should be improved
by up to ~2 mas with the ADC, making this component fundamental for
high-precision astrometry. Second, we analysed observations of a globular
cluster taken with the only currently available Multi-Conjugate Adaptive Optics
assisted camera, GeMS/GSAOI at Gemini South. Making use of previously measured
proper motions of stars in the field of view, we were able to model the
distortions affecting the stellar positions. We found that they can be as large
as ~200 mas, and that our best model corrects them to an accuracy of ~1 mas. We
conclude that future astrometric studies with MICADO requires both an ADC and
an accurate modelling of distortions to the field of view, either through an
a-priori calibration or an a-posteriori correction.
