Residuals of new data to a fitted surface

Hi all

I'm probably a bit out of my depth here, and would appreciate some help with plane fitting to 3D data and measuring distances.

I have two sets of data comprised of x, y, z coordinates. For the first set of data I fitted a plane and I can get the distances from the plane to each point from fitOutput.residuals: (unless I'm not understanding the residuals)

ft = fittype('poly11');
[fitResults, gof, fitOutput] = fit([zData, yData], xData, ft);
residuals = fitOutput.residuals;

Now I would like to get the residuals (distances) of another set of data to this same plane. I have been pouring over help files all afternoon, but with no joy.

Can anyone take pity and makes some suggestions please?

Many thanks,

Michael.