A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2019 Dec 10, 16:23 -0800
There was a variation of the obrurator trick used by military intellegence photo interpreters. They were interested in seeing what changed on the ground between the times two aerial photos were taken. A projector had two light paths and would rapidly alternate projecting one photo, then the other, then back to the first one repeating the cycle very fast. Ground items that were different in the two images appeared to vibrate.