Not really sure what you are asking but you can zero your axis at any point you want, the left lower of your workpiece is a common place to have your zero position, but it could be any point you wish in relation to your workpiece. As an example if you had a 4inch by 2 inch piece you could set the X and Y zero to the lower left corner, you would then know that the centre of the piece is X2 Y1.
If this is not what you mean please shout back as someone cleverer than me may understand .
Hood