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Re: AI-GEOSTATS: The relation between variogram and covariogram (Anisotropic)

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  • Isobel Clark
    Hi In my limited experience, different sills in different directions occur for one of the following reasons: (#) you have not yet reached the total sill in one
    Message 1 of 3 , May 14, 2002
      Hi

      In my limited experience, different sills in different
      directions occur for one of the following reasons:

      (#) you have not yet reached the total sill in one or
      more directions

      (#) you have a skewed distribution and are observing a
      proportional effect

      (#) you have a discontinuity in your study area and
      are crossing it in one or more directions

      (#) you are crossing from one population group into
      another in your direction of 'maximum variance' (or
      other similar non-stationary situations)

      (#) you may have a trend

      In all of these cases the covariance function is
      inappropriate. In most of them, the semi-variogram is
      inappropriate.

      Isobel Clark
      http://geoecosse.bizland.com/0toKriging.htm


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    • jack webster
      ... ===================================================== YES. I must explain my problem, more. I considered to isotropic variogram models g1 and g2 ... - g1
      Message 2 of 3 , May 14, 2002
        --- Isobel Clark <drisobelclark@...> wrote:
        > You want to simulate data with different sills in
        > different directions?
        >
        > Isobel
        =====================================================
        YES.
        I must explain my problem, more.
        I considered to isotropic variogram models g1 and g2
        :
        - g1 in direction 0 with parameters c01, c1 and a1
        - and g2 in direction pi/2 with c02, c2 and a2
        Then I combined these models and therefore constructed
        an anisotropic variogram such as:
        g(x,y) = w(x,y) * g1 + [ 1 - w(x,y) ] * g2
        where w(x,y) is a weigthing function.
        For simulation spatial data of this model I need the
        Covariance function C(x,y) corresponding to g(x,y).
        In fact I need C(0,0) !

        Good Thanks: Webster
        ======================================================


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