Four portraits, one fixed volume. Nothing moves; you do. From A the pieces close into Leonard Cohen. Thirty-eight degrees round they are Bob Dylan, at seventy-three Albert Einstein, at a hundred and two Charles Darwin. Every view uses exactly the same 49,000 pieces.
Most pieces are small cubes. The rest are thin plates, each standing edge-on to one of the four viewpoints: that viewer sees a hairline, the other three see the plate. That is what lets four drawings share one body. Where the pieces go was computed, not drawn: start from everything all four portraits agree on, then add and remove pieces one at a time, keeping every change that brings the four shadows closer to the four faces.
The overlap figures are measured, not estimated: every piece is projected from each viewpoint and compared, area for area, with the portrait at the sculpture's own grain. The viewpoints are the calculated ones: Dylan is seen from a little above, Einstein from a little below, Darwin from higher still.
The same idea, simpler: plates that turn and two faces, ninety degrees apart.