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AI-GEOSTATS: Universal Kriging in ArcInfo

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  • Jason Sawle
    Hello This is my first time on the list and I hope this question is going to the right place. My appologies if not. I am using Arc/Info 7.2.1 on an NT
    Message 1 of 4 , Jan 16, 2001
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      Hello

      This is my first time on the list and I hope this question is going to
      the right place. My appologies if not.

      I am using Arc/Info 7.2.1 on an NT workstation.
      With GRID I am using linear universal kriging to produce maps of heavy
      metal concentration from 127 sample points.

      Could anyone tell me what c0 and b mean. These appear at the start of
      the interpolation proceedure. I have values of 0 and 11580.591
      respectively and I am unsure of what they imply about this method.

      Thanks for your time with this.

      Jason Sawle

      ###############################################################
      Department of Geography
      Canterbury Christ Church University College
      North Holmes Road,
      Canterbury, Tel: 01227 782337
      Kent, Fax: 01227 767531
      CT1 1QU, email: j.sawle57@...
      United Kingdom http://www.cant.ac.uk


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    • Martin Roseveare
      Hi, I would be very uncertain about the validity of the zero nugget in your case as sampled variables such as you describe seem to be almost guaranteed to have
      Message 2 of 4 , Jan 16, 2001
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        Hi,

        I would be very uncertain about the validity of the zero nugget in
        your case as sampled variables such as you describe seem to be
        almost guaranteed to have some nugget from small-scale
        environmental differences alone. Do you have the option of
        specifying a variogram in ArcInfo? Are your samples evenly
        distributed throughout the area you are kriging?

        Martin Roseveare

        > Hello
        >
        > This is my first time on the list and I hope this question is going to the
        > right place. My appologies if not.
        >
        > I am using Arc/Info 7.2.1 on an NT workstation.
        > With GRID I am using linear universal kriging to produce maps of heavy
        > metal concentration from 127 sample points.
        >
        > Could anyone tell me what c0 and b mean. These appear at the start of the
        > interpolation proceedure. I have values of 0 and 11580.591 respectively
        > and I am unsure of what they imply about this method.
        >
        > Thanks for your time with this.
        >
        > Jason Sawle
        >
        > ###############################################################
        > Department of Geography
        > Canterbury Christ Church University College
        > North Holmes Road,
        > Canterbury, Tel: 01227 782337
        > Kent, Fax: 01227 767531
        > CT1 1QU, email: j.sawle57@...
        > United Kingdom http://www.cant.ac.uk


        ________________________________
        Martin Roseveare
        ArchaeoPhysica Ltd.
        Phone: 07050 369789
        Fax: 07050 369790
        email: mail@...
        web: http://www.archaeophysica.co.uk

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      • Patrick van Laake
        Dear listmembers, I tried to send this before, but I don t think anybody but Jason has seen it. If you have, sorry for the inconvenience. (List Manager, maybe
        Message 3 of 4 , Jan 17, 2001
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          Dear listmembers, I tried to send this before, but I don't think anybody but Jason has seen it. If you have, sorry for the inconvenience. (List Manager, maybe it is possible to put ai-geostats@... first and
          then the author such that a simple reply to a post works?)

          >Hello
          >
          >This is my first time on the list and I hope this question is going to
          >the right place. My appologies if not.
          >
          >I am using Arc/Info 7.2.1 on an NT workstation.
          >With GRID I am using linear universal kriging to produce maps of heavy
          >metal concentration from 127 sample points.

          In response to the replies of Isobel Clark and Martin Rosevaere and as a
          general warning to yourself: Yes, ArcInfo does automatically produce a
          semi-variogram and you can specify its functional form (the {method} optional
          parameter). Beware, however, of the method that is applied to parameterize the
          variogram. As is stated in the help file, the Levenberg-Marquardt (LM)
          algorithm is applied. LM is a non-linear least squares method of function
          estimation from sampled data. It works by minimizing chi square over the
          sampled data >>>> using the standard deviations of the individual samples
          <<<<. ArcInfo kriging does not ask for, therefore does not know of nor use the
          standard deviation of the sample data (your point cover). Instead, and this
          completely invalidates ArcInfo kriging IMHO, you specify either a number of
          neighbouring sample points or a radius from which to pick sample points to
          calculate local sample standard deviation. THIS IS COMPLETELY AND ABSOLUTELY
          WRONG!!!!! It undermines the essence of kriging. Do not use kriging in ArcInfo
          if you are trying to do serious work, or if your sample data is of high
          quality. Use a proper tool instead.

          And to conclude an excerpt from ArcInfo help on kriging:

          [quote]
          Kriging is a complex procedure that requires greater knowledge about spatial
          statistics than can be conveyed in this command reference. Before using the
          KRIGING command, you should have a thorough understanding of the fundamentals
          of kriging and have assessed the appropriateness of your data for modeling
          with this technique. If you do not have a good understanding of this
          procedure, it is strongly recommended that you review some of the references
          listed at the end of this command reference.
          [unquote]

          If you have a good understanding of kriging and KRIGING, don't use ArcInfo!

          Patrick van Laake
          ESRI Certified ArcInfo Instructor (really but ;-) )



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