Shadown Calculations

Im pretty versed in architectural drawings as well as technical illustrations I have come across something very interesting I am trying to figure out. I have seen this very rarely but how are guys calculating shadows in their drawings. specifically the round areas they are using some type of method or system which is producing very accurate shadows. I emailed the guy in the first picture but he refused to tell me how he did lol. He is able to calculate the shadows on the parts and the cast shadows as well. very accurately. I have never seen this before and nor was I tough In school about this. But anybody have idea or better any books dealing with this subject matter

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