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I want to perform an Inverse distance weighted (IDW) interpolation to a series of points. However my data set can be categorical or binary and just like the IDW I want to interpolate the new values (categorical or binary) based on the highest frequency of closest points values surrounding the prediction location:

A if the majority of the closest points are A

C if the majority of the closest points are C

...

In addition I want to avoid using close points that are behind a barrier, that can be a wall or just an elevation.

This is how the problem/dataset looks like: enter image description here

The grey points is the point I want to interpolate and the points behind the barriers can't be used in the process. The output of the interpolation process would be A or B, in this case probably A, since the closest points are all A.

What I am looking for is some kind of work-flow that would allow me to do this in ArcGIS, if possible I would prefer R (if anyone has any experience in doing this kind of processes in R). This is just the example how my problem looks like, I still have to implement it to a bigger extent and to many layers of points. Bear in mind that I have little experience with interpolation and that this might be a easy/dumb question. Any help/guidelines are deeply appreciated.

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The barrier definition is a bit vague. At least two more red points on the right are shadowed by the barrier from the grey point. They're not exactly 'behind' but the grey point can't see them. Or do those grey parallel lines indicate some kind of directional effect of the barriers? –  Spacedman Jan 24 '13 at 18:45
    
@Spacedman yes indeed there are some other red points that are not visible from the grey point, therefore can't be used. The drawing was just to give an idea of what I am looking for. The grey parallel lines indicate areas that can't be used in the interpolation, because they are not visible from the grey point (e.g. behind a barrier or on top of a barrier, the barrier can be for example a mountain) –  A.R Jan 25 '13 at 9:43
    
So to be clear if you draw a line from the gray point to every other point, any line that intersects a barrier feature is not included at all in the analysis for that gray point? Sometimes barrier features just mean the distance measure has to go around it, so that points behind barriers are further than straight line distances, but not effectively non-existent. –  Spacedman Jan 25 '13 at 10:39
    
A quick google search brings up this paper: sciencedirect.com/science/article/pii/S0016706107001218 - seems to use geostatistical methods and clustering rather than IDW. –  Spacedman Jan 25 '13 at 10:42
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1 Answer

up vote 1 down vote accepted

Natural Neighbor interpolation may be better suited for your categorical data. See the tip in the help and How Natural Neighbor works that indicates using 3D Analyst to create a TIN dataset using natural neighbor with breaklines, and then convert TIN to Raster.

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