To determine the ht of objects using stereoscopic parallax pairs photographs, it necessary to measure or estimate

1. Absolute stereoscopic parallax

2. Differential parallax:

h= H*dp/(p+dp)

Where,
h is ht of measured object, H is ht of aircraft above ground datum, p is absolute stereoscopic parallax at base of object being measured & dp is differential parallax.

Example: two stereo readings for reading are 10.75 & 9.63mm, so differential parallax is 1.12mm, average photo base p is 91.44mm & aircraft ht 3600ft find ht of building
h= (3600)1.12 /(91.44+1.12)= 43,56ft