Richard Jackson wrote:
I don't know why Mathcad does not return an error message when you try to do a surface plot with simple point data but it doesn't. Instead it tries to create a surface by some sort of interpolation.
Because you can plot a surface using x, y, and z vectors. As you say, it uses some form of interpolation, which does not always work so well even if the data is on an evenly spaced grid.
The few times I tried it never produced anything of use. I can't remember that I ever found any documentation describing what kind of interpolation Mathcad applies if asked to do a surface plot with three vectors.
The plot is more reliable if the x, y, z vectors are converted to X, Y, Z matrices.
This would only be possible if the data is on an evenly spaced grid (which is not the case here), right?
Fitting a surface to 3D data is simple enough using minerr, but this data does not look like a surface that could be fitted with a function with any reasonable number of parameters.
Correct, I had tried a polynomial of sixth order with 49 parameters and the result wasn't even close to useable.
Guess PTC could implement a few algorithms from Creo ;-)