Hi,
I think you can't do it, AEM adds annotation based on x and y axis for assets but not based on another dimension, though it creates a preview of annoation.
e.g.
{"dimension":{"w":1000,"h":340},"shapes":[{"path":"M 0 29 C 0 13 10 0 23 0 C 35 0 45 13 45 29 C 45 44 35 57 23 57 C 10 57 0 44 0 29 Z","box":{"x0":163,"y0":156,"x1":208,"y1":213},"strokeStyle":"#ffcc00","lineWidth":5,"domainBox":{"x0":163,"y0":458.8235294117647,"x1":208,"y1":626.4705882352941},"type":"ellipse"}],"texts":["test"]}
Arun Patidar