[STATSGRASS] gstat: problem with prediction value at point location

[Jarosław Jasiewicz]

Edzer J. Pebesma napisał(a):
> This is a well-known property of kriging if locations coincide 
> exactly: if measured, the best estimate is the measurement itself. 
Hmm. yes and no. As I remember form other program (like geostatistic 
analist in arc info) in point value wasn't exact. the difference between 
exact and predicted values in point location were used to calculate the 
RMS total (I can be wrong here, I didn't used Arc Info for over 2 years) 
before final calculation.

I I attached samples, how it looks like with point location.

It was found  during disscution when I presended some data. I was asked 
about RMS Total for my prediction (in arc info mode  - as sum of 
differences between exact and predicted values in point location). I 
tried to do this with sampling points at predicted map. In that way the 
RMS Total was 0!. I consult result with others and it seems variogram is 
OK,
(it was automatically fitted expotential vaiogram, for gaussian 
variogram result was worse).
> It's also cause of the problem that you can't have duplicate 
> observations in kriging. Even with a nugget, gamma(0)=0. You may want 
> to shift your points or your grid e.g. a few centimeters to get rid of 
> it.
it gives the same results
 regards
Jarek

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