I want to find out is the curvature between the keycap, the keys are arranged like an arc
Microsoft and Logitech make custom keycaps specifically for those keyboards, while mechanical keyboards have to use standard keycaps, each with the same square footprint.
Many of these keyboards from Microsoft or clones of them from other brands are also a little weird also in that they often
increase the row-stagger for the keys by curving the keys that way.
The "Microsoft Ergonomic Keyboard" (the official name, without any "Natural", "Sculpt" or "Surface" brand) has a little less row-stagger than other Microsoft keyboards though.
I know of only two attempts of mechanical keyboards with standard keycaps that are actually
curving the rows, and one of them is (yet) only a concept I made:
Since 2011, I've had an idea of improving the "symmetric stagger" layout by curving it a bit, but I didn't get the maths right until I revisited the idea in 2019. Then I made this sketch (generated from a Python script, and then edited in QCAD and The Gimp)
The curvature is calculated procedurally, and with collision detection to make sure that the spacing does not get too small. However, the overall width each row needs to be a bit wider than standard just to facilitate the use of standard keycaps!
I built a mockup for it also, and defined the matrix and controller in KiCad, but I never decided on how to lay out the thumb keys, so this here is mostly an idea. I haven't worked on it for months now. Was supposed to be fully split and tented (along red lines), or as a compact option (without the parts outside the red lines).
Last fall there was the
GB of the Sagittarius. Maybe it will come back. It is flat with no tenting.
The right side has neither fully straight columns nor retained row-stagger but something in-between. Overall it is
in-effect a column-stagger with rotated keycaps like mine but with larger column offsets.
The left hand's keys are more like the Alice though, only curved somewhat. I believe they used a constraint-optimising algorithm for theirs.
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Among columnar split keyboards, there are those that lay out columns in various ways though. Several examples exist where the columns spread out like the fingers on the hand.
The Willow64 and WillowPecoe curve the
columns instead of the rows.