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[ai-geostats] Typical sample sizes for variogram calculations

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  • Mark Coleman
    Greetings, I am coding some basic geostatistical procedures and was curious about the typical sorts of sample sizes researchers run into. I know that sizes
    Message 1 of 4 , Nov 3, 2004
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      Greetings,

      I am coding some basic geostatistical procedures and was curious about
      the "typical" sorts of sample sizes researchers run into. I know that
      sizes of n=1000 are fairly common. How about sizes of N=10,000 or
      greater? Are variograms computed on samples this large?

      Thanks,

      -mark
    • Dan Cornford
      Mark, this really depends on how you want to estimate the parameters of the covariance / variogram. If you want to use maximum likelihood, then due to the need
      Message 2 of 4 , Nov 4, 2004
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        Mark,

        this really depends on how you want to estimate the parameters of the
        covariance / variogram. If you want to use maximum likelihood, then due
        to the need to invert a matrix, which is O(n^3), generally sizes above
        about 1000 become rather prohibitive on a desktop computer. One possible
        alternative that attempts to retain statistical rigour but scale
        gracefully with sample size is our Sparse Sequential method:

        http://www.ncrg.aston.ac.uk/~csatol/ogp/index.html

        Alternatively you could use methods of moment estimators (i.e. the
        classic sample variogram) and fit these empirically using some function.
        Note that in computing the sample variograms one can work in a
        sequential fashion, so that not all pair comparissons need be stored,
        but they must be computed .... so it will be slower, scaling as O(n^2)
        in the computation of the sample variogram.

        cheers

        Dan

        Mark Coleman wrote:
        > Greetings,
        >
        > I am coding some basic geostatistical procedures and was curious about
        > the "typical" sorts of sample sizes researchers run into. I know that
        > sizes of n=1000 are fairly common. How about sizes of N=10,000 or
        > greater? Are variograms computed on samples this large?
        >
        > Thanks,
        >
        > -mark
        >
        >
        >
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        --

        Dr Dan Cornford d.cornford@...
        Computer Science
        Aston University
        Aston Triangle tel +44 (0)121 204 3451
        Birmingham B4 7ET fax +44 (0)121 333 6215

        http://www.ncrg.aston.ac.uk/~cornfosd/
      • Isobel Clark
        Mark Our free downloadable data sets range from 16 to over 20,000. The biggest set I worked wth was a small section of a South African gold mine - 450,000.
        Message 3 of 4 , Nov 4, 2004
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          Mark

          Our free downloadable data sets range from 16 to over
          20,000. The biggest set I worked wth was a small
          section of a South African gold mine - 450,000.

          Isobel
          http://geoecosse.bizland.com/softwares
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