Spline - exact interpolation?

Discussion created by stefan.haglundesri-se-esridist Employee on Oct 26, 2011
Latest reply on Oct 28, 2011 by stefan.haglundesri-se-esridist
Hi folks,

I have to create a surface from points where the value in the surface at the location of each point is exactly the same as the z-value in the point.

To me, it seems that the Spline interpolator (from Spatial Analyst) should do exactly this. Reading from the help it says:
�??The Spline tool uses an interpolation method that estimates values using a mathematical function that minimizes overall surface curvature, resulting in a smooth surface that passes exactly through the input points.�?�

To test if it really worked the way I expected, I used the Extract Values to points tool without the option to interpolate to draw the values from the pixels in the same location as my points. Looking at the resulting table, there is a difference of up to 20 percent in the values from my original points and the raster.

I found this thread in the Geostats forum, but it doesn't answer the question either.

Can anyone give an explanation for why this is happening or perhaps a way to achieve the goal? Is there a setting in the Spline tool I am missing perhaps?