The black hole at the Galactic centre exhibits regularly flares of radiation , the origin of which is still not understood .
In this article , we study the ability of the near-future GRAVITY infrared instrument to constrain the nature of these events .
We develop realistic simulations of GRAVITY astrometric data sets for various flare models .
We show that the instrument will be able to distinguish an ejected blob from alternative flare models , provided the blob inclination is \gtrsim 45 ^ { \circ } , the flare brightest magnitude is 14 \lesssim m _ { \mathrm { K } } \lesssim 15 and the flare duration is \gtrsim 1 h 30 .