3D Spline from 3D Scatter

I currently have a plot that looks like:

     figure;
     x = randn(1,1000);
     y = randn(1,1000);
     z = x.*y;                          
     tri = delaunay(x,y);
     [r,c] = size(tri);
     h = trisurf(tri, x, y, z);
     hold all;
     h2=scatter3(x,y,z,'filled');which is nice. great.

however, I would like to generate a spline function for this surface, which would then allow me to evaulate it using fnval.m and plot it using fnplt.m etc

Is there anyway to generate this spline function using spaps.m or cspaps.m?

Please could you provide an example.

thanks