Hi Eric, I am guessing that the sampling density in 3D is small, hence at the beginning of the simulation procedure when the grid is essentially empty the estimate depends mainly on the type of trend model you adopt, i.e. a global mean for SK or a locally re-estimated local mean for OK. It looks like your estimate of the local mean is not very good and this might biase your simulation right from the beginning. Are you using a multiple grid strategy and did you notice a higher proportion of order relation deviations when using OK versus SK? Note that in the recent Stanford software GEMS, sequential indicator simulation is available only with the SK option, which might indicate some problems with the OK option...
Hope it helps, Pierre <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Dr. Pierre Goovaerts President of PGeostat, LLC Chief Scientist with Biomedware Inc. 710 Ridgemont Lane Ann Arbor, Michigan, 48103-1535, U.S.A. E-mail: [EMAIL PROTECTED] Phone: (734) 668-9900 Fax: (734) 668-7788 http://home.comcast.net/~goovaerts/ <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> On Mon, 3 Jan 2005 [EMAIL PROTECTED] wrote: > Hello all. I'm performing unconditional sequential indicator simulation over > a 3D domain. As the method requires, I have specified the data cdf at (10) > thresholds, and have also defined parameters for an (exponential) variogram > at each threshold. When I run the simulation algorithm using simple kriging > to estimate the cdf at each threshold for each node, the method works great, > i.e., I am able to approximatley reproduce the domain cdf and variograms. > However, when I use ordinary kriging, the method falls apart. It seems that > reproduction of the domain cdf becomes 'blocky' and looses its smoothness. I > have made the search ellipsoid very large and allowed the number of data > points that can be used for the OK to be very large, but the results are > always poor. Does anyone have any suggestions about what is happening with > the OK? I am using GSLib software. Thanks to all! > > Eric Bhark > > >
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