  Estimating the metric height of a person from monocular imagery without
additional assumptions is ill-posed. Existing solutions either require manual
calibration of ground plane and camera geometry, special cameras, or reference
objects of known size. We focus on motion cues and exploit gravity on earth as
an omnipresent reference 'object' to translate acceleration, and subsequently
height, measured in image-pixels to values in meters. We require videos of
motion as input, where gravity is the only external force. This limitation is
different to those of existing solutions that recover a person's height and,
therefore, our method opens up new application fields. We show theoretically
and empirically that a simple motion trajectory analysis suffices to translate
from pixel measurements to the person's metric height, reaching a MAE of up to
3.9 cm on jumping motions, and that this works without camera and ground plane
calibration.
