Re: [Sgems-users] Exponential model in sgems

[Pierre G. <goo...@te...>]

Dear Sara,

The practical range of the exponential model in S-GeMS corresponds to
what is called the "effective" range in Gslib.
The choice of indicator kriging versus multiGaussian kriging depends on
several factors,
and the shape of the histogram might not be the critical one. Factors
include the existence
of a large proportion of observations with the same value (e.g. data below
the detection limit),
or the asymmetry in the spatial continuity of low and high values. In all
situations, cross-validation
could help deciding which method to adopt.. These last few months I have
been involved
with the modeling of contaminated sediments at several sites and
multiGaussian kriging was
adopted based on cross-validation results. Also, I recently published a
paper in Computers
& Geosciences and the associated computer code that implements all the steps
of indicator
kriging, including the modeling of all indicator variograms &
cross-validation/jack-knife with
generation of accuracy plots, automatically.

Regards,

Pierre

On Tue, Feb 17, 2009 at 6:00 AM, sara sabri <sar...@ya...> wrote:

> Dear list
> waht is the range of an exponential model in s-gems? i.e. practical range
> should be used? Is it the same with GSLIB?
> And finally with a data of relatively normal distribution which methods
> should I use to model the conditional probability? Is SISIM justified? Or I
> have to use it only in case of asymetric distribution of categorical
> variable?
> I really appreiate your comments.
> Thanks in advance
> Sara
>
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Pierre Goovaerts

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