well you have one axis set with the plate
isn't it knees to shoulders? just put some chip in the uniform. max value for shoulder x and min value for knee chip
have the projection from the uniform cross reference with that of the plate and you have a 3D strike zone at all times
Knees and around belly button I believe. Its really up to the umpire which is part of baseball. Some have small strike zones, some have huge ones.
I get that people hate that, but its kind of fun to watch a pitcher or batter adjust to that.
Also, they go through tons of balls in a game AND putting chips in players uniforms will inevitably lead to cheating. We all know thats the one thing baseball players are damn good at.