Topo to Raster: Interpolated cell is not matching real cell value

[Nathanvan_Oort]

Hello,

I am in the process of creating geologic formation surfaces (both top, and bottom) using the tool, "Topo to Raster". My "Primary type of input data" is set to "Spot", and I am choosing "NO_ENFORCE" on "Drainage enforcement"... Also, I have a snap grid for my study so everything is lined up perfectly.

I am using point data from wells that have bottom and top formation depths as my input (Type= Point Elevation) to interpolate a bottom and top surface as a raster.  When I create my top surface, my interpolated values do not match my real top surface cell values... the same for the bottom surface.  I then subtract my bottom surface from my top surface to create a thickness using "Raster Calculator"... but for some reason the thickness value that is calculated does not equal that of my real thickness value that is known in many cases.

For example: I have a point data for a well that has a top depth of 946, and a bottom depth of 211 (the real thickness = 735).   My interpolated value for the same well for the top depth is 949, and a bottom depth of 203 (interpolated thickness= 746).

Has anyone else run into this issue? Why is it that my interpolated values do not match my real measured values that are my main input in "Topo to Raster"?

Thanks for your help!

[DanPatterson_Retired]

There are some caveats in the tool Topo to Raster—Help | ArcGIS for Desktop

specifically relating to the number of points that may fall within a cell, hence it is important to specify a cell size in the Environments tab of the tool along with the extent and snap raster.  confirm those inputs as well prior to assessing results.  There is also no statement that the exact elevation for the input points will be returned, if that is what you are looking for.

[Nathanvan_Oort]

We were hoping the input cell values would be returned as the interpolated

values for our analysis. We appreciate the quick response though. Do you

have any recommendations for another interpolation tool that allows

multiple inputs? We've tried kriging, IDW, natural neighbour, and topo to

raster thus far.

Thanks,

Nathan

[SteveLynch]

TopoToRaster uses an iterative spline technique to primarily create DEMs and is not an exact interpolator.

See Deterministic methods for spatial interpolation​

-Steve