As part of my request/justification to go to the UC I had to fend off the claim from management that Manifold can't do surfaces as well as ArcGIS (3D Analyst), this was partly my fault for not using Manifold to generate surfaces for random points (I'd been using Surfer to achieve this), I commonly use boreholes and water well records as sources, mainly because I had not investigated thoroughly the variety of methods and models available in Manifold. With the incentive of dismissing the 'ArcGIS is better than Manifold' carrot dangling in front of me it didn't take me long to figure out that using Kriging with the Linear variogram in Manifold produces much better results for this kind of randomly placed data.

The reason for the comment from management related to a surface that was generated by another consultant using IDW interpolation with 3D Analyst. I used the Kriging/Linear method on the same data and to be honest I don't think either IDW or Kriging produced results that weren't far from the mark. This quote of a quote felt quite relevant in this case:

"Interpolation is a black art, and interpolation methods should never be trusted. Careful researchers always interpolate several times using different methods, and choose the result they dislike least." ~ Roger Bivand

Isn't it about time Manifold added IDW as another interpolation method? I'd have thought it being in ESRI products already would be reason enough.

Actually Brian, I am less interested in IDW, and more interested in the ability to create a variogram. IDW and kriging are of little use personally, unless you can see the variogram to determine the spatial structure of the data. Therefore, I either use another product for geostatistics, or create my variogram in SQL. Its alittle ugly, but it does in fact work :-)

That said, IDW is really computationally easy to do, and should be incorporated into Manifold.

I agree creating variograms would be a good addition - some of us would have to get studying to understand the nuances of tweaking them and the subsequent results they produce

I sent my suggestion to Sales for IDW in any case.

I heard another quote:

"everyone believes the results of a model, except the guy who developed the model"

Great quote ... I think this should be a standard disclaimer added to all GIS maps and outputs

'All models are wrong, but some of them are useful'

These books are good:

Smoothing Methods in Statistics

Applied Smoothing Techniques for Data Analysis

Hi Art,

do you have or would you be wiling to post the code in SQL that use to create variogram?

m