I have found a neat solution to my problem, but only for 2d curve fitting.
It is titled, least square curve fitting with confidences.

The equation of the parabolic fit version is as following:-

y = b0 + b1*z + b2*(z^2)

where b0, b1, and b2 are calculated from the least squares solution of the
following matrix set up.

| s0 , sz , szz | | b0 | | sy |
| sz , szz , szzz | | b1 | = | szy |
| szz , szzz , szzzz | | b2 | | szzy |

where s0 = Sum between i = 1 and n of pi
sy = Sum between i = 1 and n of (yi * pi)
sz = Sum between i = 1 and n of (zi * pi)
szz = Sum between i = 1 and n of ( zi * zi * pi)

pi is a confidence constant.

I now need to expand is idea to 3d, I have been told it is possible, but not
how to do it.

Any idea folks?

Adam