I'm an astrophysicist in high energy gamma ray astronomy.
Or telescope sensors have hexagonal pixels.
You website is awesome and helped a lot writing the coordinate trafos and other stuff. We always recommended it to everyone involved.
One switch I always wished it had was to switch to a cartesian coordinate system where x points right, y points up and negative coordinates are allowed.
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Quite recently, some telescopes started using silicon photo multipliers, which are mostly square by design.
But: The first telescope to use those also used light concentrators to increase the detector area and these have hexagonal entrance windows, so we also have hexagonal pixels.
Physicists like symmetries, and light concentrators are more effective when round than square, hexagonal is a good middle ground.