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What quality can I expect to reach with shape measurement?

I am thinking of using OpenCV to find the position and size of a rectangular sheet placed on the table of a CNC router.

It would be something similar to what's described here, but with a larger table (3m x 3m), with two or three reference targets (instead of one dime) and with one rectangular shape (instead of a few pills or other objects).

If you tell me that sub-millimeter precision in the position of a 1m x 2m rectangle is impossible to reach, then I won't even try.

But if you tell me that there is a chance, please let me know what are the most critical part of such a system and I will give it a try.

What quality can I expect to reach with shape measurement?

I am thinking of using OpenCV to find the position and size of a rectangular sheet placed on the table of a CNC router.

If you tell me that sub-millimeter precision in the position of a 1m x 2m rectangle is impossible to reach, then I won't even try.

But if you tell me that there is a chance, please let me know what are the most critical part of such a system and I will give it a try.

EDIT (following the comment of David_86)

Assuming that I can move the camera, would it help more zooming in and panning so I can stitch together more images, so I have one larger/higher resolution image, or taking more photos from slightly different positions and orientations and then average the result?

My intuition says that the stitching process could introduce some error, while averaging several measurement should improve the quality, (but I don't trust my intuition, that's why I'm here.)