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RE: [ai-geostats] a questions of using GSTAT to do Gaussian Condi tional Simulation!

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  • Shazly, Salah DSC92
    Dear All, Are there any rules help building stable variograms, like number of lags, range ..etc? And what is the minimum number of control points needed to
    Message 1 of 2 , Jul 8, 2004
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      Dear All,

      Are there any rules help building stable variograms, like number of lags,
      range ..etc? And what is the minimum number of control points needed to
      build a variogram?

      I am working on a subsurface oil field reservoir.

      Regards,



      ____________________________________________________________
      Salah el-Shazly (DSC/92)
      Geologist Consultant
      PDO Study Centre

      Petroleum Development Oman
      PO Box 81, PC 113
      Muscat, Sultanate of Oman
      Phone: +968 674135,
      GSM: +968 7212 8680,
      Fax: 968 674870
      E-mail: salah.shazly@...
      selshazly@...


      -----Original Message-----
      From: Ernesto Jardim [mailto:ernesto@...]
      Sent: Wednesday, July 07, 2004 19:45
      To: Feng Liu
      Cc: ai-geostats@...
      Subject: Re: [ai-geostats] a questions of using GSTAT to do Gaussian
      Conditional Simulation!

      Hi,

      Why don't you use gstat within R ?

      At least the 2 last questions will be solved.

      Regards

      EJ

      On Wed, 2004-07-07 at 16:09, Feng Liu wrote:
      > st1\:* { BEHAVIOR: url(#default#ieooui) } --> -->
      > Hi, Dear List:
      >
      > I am trying to use Gstat to do Gaussian Conditional Simulation on my
      > soil C content data. I got 3 questions as following:
      >
      > 1. If I use "set nsim=100" to do 100 times simulation, does the
      > simulations follow a single random path or they will follow 100
      > different random paths? What should I do if I want to let them follow
      > different random paths.
      >
      > 2. Is it possible for me to write all the results of 100 simulations
      > to one single file? How?
      >
      > 3. Gstat needs gnuplot to do the plot, but I could not get gnuplot
      > compiled and start in windows, could you please tell me how to do it
      > if you have experience on this.
      >
      > Thanks a lot
      >
      > Feng Liu
      > Graduate Student
      > Texas A&m University
      >
    • Ernesto Jardim
      ... Hi, Building a stable variogram is like magic ! You have to be a sorcerer, a good one, to deal with everything that matters and make it through the evil
      Message 2 of 2 , Jul 8, 2004
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        On Thu, 2004-07-08 at 08:36, Shazly, Salah DSC92 wrote:
        > Dear All,
        >
        > Are there any rules help building stable variograms, like number of lags,
        > range ..etc? And what is the minimum number of control points needed to
        > build a variogram?
        >
        > I am working on a subsurface oil field reservoir.
        >
        > Regards,
        >

        Hi,

        Building a "stable" variogram is like magic ! You have to be a sorcerer,
        a good one, to deal with everything that matters and make it through the
        "evil forest of variogram modelling".

        In this list there are some of the best sorcerers you can get, so they
        may give you a good answer.

        There's a very good reference, in my opinion, about geostatistics that
        gives you a lot of information on the insights of variogram modelling.

        Applied Geostatistics ()
        Edward H. Isaaks, R.Mohan Srivastava

        It's a "must have" if you want to understand geostatistics and don't
        want to deal with all the mathematics. If you do that then check, p.e.

        Statistics for Spatial Data (1993)
        N. Cressie

        You may try to model covariance without using the variogram, with MLE
        methods. Take a look at geoR, a package for R.

        http://www.est.ufpr.br/geoR/

        There's also a paper about using MLS methods directly from the variogram
        cloud, check

        Muller, W.G. (1999), Least-squares fitting from the variogram cloud ,
        Statistics & Probability Letters, 43, 93-98.

        Best regards

        EJ

        --
        Ernesto Jardim <ernesto@...>
        Biólogo Marinho/Marine Biologist
        IPIMAR - Instituto Nacional de Investigação Agrária e das Pescas
        IPIMAR - National Research Institute for Agriculture and Fisheries
        Av. Brasilia, 1400-006
        Lisboa, Portugal
        Tel: +351 213 027 000
        Fax: +351 213 015 948
        http://ernesto.freezope.org
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