How to obtain an accurate, smooth terrain model from a set of 3d points?

Hi everybody.

I have a little task to do. I have a file containing a set of 3d points that are the result of a topographic survey of a piece of land.

What I need is to obtain a 3d model of the piece of land and the topographic contour lines of it.

The first approach I came out with is to create a delaunay mesh and then smooth it with the WeaverBird's Loop Smoothing component, as the original mesh is too edgy to obtain any nice contour line. But I am not fully satisfied with this approach as the resulting smoothed mesh is not accurately passing through the vertices of the delaunay mesh, which are the only points of which I know the exact position. In fact it seems that those are the points in which the difference between the original and the smoothed mesh reaches its highest value. Do you know any better interpolation algorithm that doesn't affect the position of vertices of the original mesh?

Thanks a lot!