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

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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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