[R-sig-Geo] How to locate local minima points on a Krige-fitted surface?

[Paul Hiemstra]

Dear Jeff,

I think you cannot escape discretizing your kriging surface as there is 
no mathematical expression that captures the kriging surface. To use 
optim you could make an objective function that was two inputs, x and y 
location. The functions calls the fields package to estimate the kriging 
prediction at this point and returns it. This ofcourse assumes that the 
variogram model is known. You have to play with the settings of optim to 
get it working and prevent a local minimum. You could take a look at 
SANN (simulated anealing) which is part of optim.

cheers,
Paul

On 06/11/2010 07:24 AM, v v wrote:
>
> Hi,
>
> I am using the 'fields' package to conduct Kriging interpolation on my dataset. I have managed to generate the 3-dimensional surface plot of the Krige-fitted surface. There are several local minima points on the surface. My main interest is to pinpoint the exact x-y coordinates of the lowest response (elevation) point of each of the local minima points.
>
> Although an approximation is possible by generating predicted values using a regularly-spaced grids, such approximations are not good enough for my purposes. I have intentions to use the optim() and/or constrOptim() functions to locate the minima but I do not know what is the objective function to be optimized. Therefore, so far, I am still unable to do that.
>
> So, know how can I locate the local minima on a Krige-fitted surface?
>
> regards,
> Jeff Yeo 		 	   		
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-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
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