I was scanning satellite photos yesterday and came across what I think are ground reference points built to enable determination of exact ground distances using

I was scanning satellite photos yesterday and came across what I think are ground reference points built to enable determination of exact ground distances using a series of concentric rings and oriented linear features. I believe knowledge of the exact diameter of the rings and length of the chords would allow a user to measure features in the photo with acceptable precision. I know that early pilots had a series of markers that they could use to keep themselves on track as they flew their long distance routes. These things were oriented concrete markers, some of which are still accessible. We all need a reference, a way to cross-check or ground truth our results and conclusions.