Loading ...
Sorry, an error occurred while loading the content.

Re: AI-GEOSTATS: Kriging with External Drift

Expand Messages
  • Andreas Hartmann
    Hi, a little off the original topic, but one question that puzzles me is the computation of the semivariogramm for Kriging with external drift. If I understand
    Message 1 of 13 , Dec 7, 2001
    • 0 Attachment
      Hi,

      a little off the original topic, but one question that puzzles me is the
      computation of the semivariogramm for Kriging with external drift.

      If I understand correctly, a relation of type
      m*(x) = a1(x) + a2(x)*s(x)
      is assumed between the mean of the primary variable at location x
      (drift) and secondary variable (s). Now, the a's are dependent on the
      location and are not computed explicitly. But in the kriging system the
      residual covarince is needed. To compute the residuals, I would need to
      calculate the equation explicitly, right?

      How do I compute the residual semivariogramm when I don't know the
      residuals? Or have I misunderstood something in the concept of external
      drift?

      Best regards
      Andreas

      --
      Andreas Hartmann
      RWTH Aachen, Angewandte Geophysik
      Lochnerstr. 4-20
      52056 Aachen, Germany
      (+49) (-0) 241 8094835
      mailto:Andreas@...-aachen.de
      http://www.geophysik.rwth-aachen.de




      --
      * To post a message to the list, send it to ai-geostats@...
      * As a general service to the users, please remember to post a summary of any useful responses to your questions.
      * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
      * Support to the list is provided at http://www.ai-geostats.org
    • Isobel Clark
      ... you got it. Plus the constraint that the drift components in the samples have to balance with the drift component at the point being estimated. Isobel
      Message 2 of 13 , Dec 7, 2001
      • 0 Attachment
        > So are you saying that the external drift variable
        > in the matrix is just the
        > magnitude of the the drift variable at that point?
        you got it.

        Plus the constraint that the drift components in the
        samples have to balance with the drift component at
        the point being estimated.

        Isobel

        ________________________________________________________________
        Nokia 5510 looks weird sounds great.
        Go to http://uk.promotions.yahoo.com/nokia/ discover and win it!
        The competition ends 16 th of December 2001.

        --
        * To post a message to the list, send it to ai-geostats@...
        * As a general service to the users, please remember to post a summary of any useful responses to your questions.
        * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
        * Support to the list is provided at http://www.ai-geostats.org
      • sshibli@mac.com
        ... There is a nice section (Chapter 5.4) in Cressie s textbook (Statistics for Spatial Data) that discusses the potential bias of estimating semivariograms
        Message 3 of 13 , Dec 7, 2001
        • 0 Attachment
          On Friday, December 7, 2001, at 10:05 AM, Andreas Hartmann wrote:
          >
          > How do I compute the residual semivariogramm when I don't know the
          > residuals? Or have I misunderstood something in the concept of external
          > drift?

          There is a nice section (Chapter 5.4) in Cressie's textbook (Statistics
          for
          Spatial Data) that discusses the potential bias of estimating
          semivariograms from residuals and Matheron's formulation of
          IRF-K kriging as an alternative means to krige in the presence of
          a trend. The iterative fitting of the covariance is usually
          non-graphical,
          which is a drawback in itself, and Fig. 5.1 in the same section shows
          Cressie's bold attempt at showing the pitfalls of doing such an
          "automatic" fit. I have not used IRF-K kriging very much in practice,
          for the above reasons. Better to live with the devil that I know, i.e.
          my -- albeit biased -- residual variogram.

          Regards,

          Syed



          --
          * To post a message to the list, send it to ai-geostats@...
          * As a general service to the users, please remember to post a summary of any useful responses to your questions.
          * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
          * Support to the list is provided at http://www.ai-geostats.org
        • Nicholas Lewin-Koh
          Hi, Just to add to that Gotway and cressie I can t remember the exact citation did a large simulation study and showed that the bias from using the residual
          Message 4 of 13 , Dec 8, 2001
          • 0 Attachment
            Hi,
            Just to add to that Gotway and cressie I can't remember the exact citation
            did a large simulation study and showed that the bias from using the
            residual variogram is very small in most cases.

            Nicholas

            On Fri, 7 Dec 2001 sshibli@... wrote:

            >
            > On Friday, December 7, 2001, at 10:05 AM, Andreas Hartmann wrote:
            > >
            > > How do I compute the residual semivariogramm when I don't know the
            > > residuals? Or have I misunderstood something in the concept of external
            > > drift?
            >
            > There is a nice section (Chapter 5.4) in Cressie's textbook (Statistics
            > for
            > Spatial Data) that discusses the potential bias of estimating
            > semivariograms from residuals and Matheron's formulation of
            > IRF-K kriging as an alternative means to krige in the presence of
            > a trend. The iterative fitting of the covariance is usually
            > non-graphical,
            > which is a drawback in itself, and Fig. 5.1 in the same section shows
            > Cressie's bold attempt at showing the pitfalls of doing such an
            > "automatic" fit. I have not used IRF-K kriging very much in practice,
            > for the above reasons. Better to live with the devil that I know, i.e.
            > my -- albeit biased -- residual variogram.
            >
            > Regards,
            >
            > Syed
            >
            >
            >
            > --
            > * To post a message to the list, send it to ai-geostats@...
            > * As a general service to the users, please remember to post a summary of any useful responses to your questions.
            > * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
            > * Support to the list is provided at http://www.ai-geostats.org
            >

            CH3
            |
            N Nicholas Lewin-Koh
            / \ Dept of Statistics
            N----C C==O Program in Ecology and Evolutionary Biology
            || || | Iowa State University
            || || | Ames, IA 50011
            CH C N--CH3 http://www.public.iastate.edu/~nlewin
            \ / \ / nlewin@...
            N C
            | || Currently
            CH3 O Graphics Lab
            School of Computing
            National University of Singapore
            The Real Part of Coffee kohnicho@...


            --
            * To post a message to the list, send it to ai-geostats@...
            * As a general service to the users, please remember to post a summary of any useful responses to your questions.
            * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
            * Support to the list is provided at http://www.ai-geostats.org
          Your message has been successfully submitted and would be delivered to recipients shortly.