How to interpolate gridded data like "surf"

Hi,

I got 3d-gridded data (2D input, 1D Output), bust jut not in the meshgrid format. What is an efficient way to interpolate from the two inputs to the output? Apparently the "surf" command is already very capable of doing this, but just for plotting the data. As the grid is not perfectly aligned "griddata" is not so accurate and also rather slow.

Thanks a lot for your help!

Nils