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Re: GEOSTATS: Problems with Kriging in Splus

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  • Melanie Wall
    The krige function in S+Spatial uses the covariogram instead of the variogram. So in general it can only do ordinary kriging on 2nd order stationary processes
    Message 1 of 4 , Dec 7, 1999
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      The krige function in S+Spatial uses the covariogram instead of the
      variogram. So in general it can only do ordinary kriging on 2nd order
      stationary processes (i.e. where the covariogram exists). The theoretical
      covariograms it supports are expondential, spherical and gaussian models.
      Apparently this function can also be tricked to work with a linear
      variogram model (see p. 98 of S+Spatial Stat manual).

      -----------------------
      Melanie Wall
      Division of Biostatistics
      A460 Mayo Building Box 303
      420 Delaware Street S.E.
      Minneapolis, MN 55455
      (612)625-2138
      melanie@...

      On Tue, 7 Dec 1999, Fay Hughes wrote:

      > Hello
      >
      > I am presently working with S+Spatial Stats (Splus 2000), trying to
      > repeat results I obtained previously with Geoeas, but am encountering
      > difficulties, when trying to get Splus to give predictions on a small
      > (eg 2x2) grid which is a subsection of the whole area, the .Fortran
      > fault "Covariance matrix is not positive definite" results, even though
      > Geoeas can perform the same kriging.
      >
      > I was also wondering if the code for the krige and predict.krige
      > functions are available and also if there is anyway in Splus to specify
      > search radii (like in geoeas) or to get more detailed information about
      > the actual procedure (like caps, scroll and num lock in Geoeas).
      >
      > Thank you, in anticipation of your help.
      >
      > Fay Hughes (Miss)
      > email: HughesFA@...
      >
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    • Inge Frette
      Hello folks, not being an expert in geostatistics I wonder why the power model of the variogram model in Gslib is not allowed for when doing cokriging ? Anyone
      Message 2 of 4 , Dec 13, 1999
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        Hello folks,
        not being an expert in geostatistics I wonder why the power model of the
        variogram model
        in Gslib is not allowed for when doing cokriging ?

        Anyone that knows why ?

        Regards from Inge Frette


        ************************************************************************
        Inge Frette Phone : +47 51 87 54 50
        GEOLOGICA AS Phone : +47 51 87 58 15 (from 1.1.2000)
        P.O.Box 8034 Fax : +47 51 87 52 87
        N-4003 STAVANGER E-mail: inge.frette@...
        NORWAY Web : http://www.geologica.no
        ************************************************************************

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      • Pierre Goovaerts
        Hello, Power models are not allowed for SIMPLE cokriging in the current version of cokb3d although they are allowed for simple kriging. Note that simple
        Message 3 of 4 , Dec 13, 1999
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          Hello,

          Power models are not allowed for SIMPLE cokriging
          in the current version of cokb3d although they
          are allowed for simple kriging.
          Note that simple (co)kriging systems need to be expressed in
          terms of covariances but pseudo-variances can be used
          to convert unbounded semivariograms into covariances.

          My advice is: Do not use simple cokriging since the
          assumptions of stationarity of the means are rarely met.
          Use the option ordinary cokriging and compare the
          two options: traditional and standardized cokriging since
          the unbiasedness constraints can influence the quality
          of the predictions, e.g. see
          Goovaerts, P. 1998. Ordinary cokriging revisited.
          Mathematical Geology, 30(1):21--42.

          Cheers,

          Pierre
          <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

          ________ ________
          | \ / | Pierre Goovaerts
          |_ \ / _| Assistant professor
          __|________\/________|__ Dept of Civil & Environmental Engineering
          | | The University of Michigan
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          On Mon, 13 Dec 1999, Inge Frette wrote:

          > Hello folks,
          > not being an expert in geostatistics I wonder why the power model of the
          > variogram model
          > in Gslib is not allowed for when doing cokriging ?
          >
          > Anyone that knows why ?
          >
          > Regards from Inge Frette
          >
          >
          > ************************************************************************
          > Inge Frette Phone : +47 51 87 54 50
          > GEOLOGICA AS Phone : +47 51 87 58 15 (from 1.1.2000)
          > P.O.Box 8034 Fax : +47 51 87 52 87
          > N-4003 STAVANGER E-mail: inge.frette@...
          > NORWAY Web : http://www.geologica.no
          > ************************************************************************
          >
          > --
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          > of any useful responses to your questions.
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          > DO NOT SEND Subscribe/Unsubscribe requests to the list!
          >

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