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2438Re: [ai-geostats] Re: Software for Automatic Semivariogram Estimation

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  • Behrang Kushavand
    Feb 28, 2006

      Dear Prof. Clark

      Here is the paper:

      http://www.ansinet.org/fulltext/jas/jas581405-1407.pdf

      Formula (4) is the weight factor.

      King regards.

      Behrang.

       

       

      ----- Original Message -----
      Sent: Tuesday, February 28, 2006 9:53 PM
      Subject: [ai-geostats] Re: Software for Automatic Semivariogram Estimation

      Behrang
       
      What weighting do you use in the weighted least squares?
       
      Isobel
      http://www.kriging.com

      Behrang Kushavand <Kushavand@...> wrote:
      hi,
      I have a software for Variogram AUTO Modeling (winvam) that works with gslib
      (GAMV.exe).

      First you must calculate experimental variogram (omni or directional) with
      gamv.exe and then by using winvam, you can fit the best model by least
      square and weights least square criteria for given model(s),

      You can find it at:

      http://www.ai-geostats.org/software/Geostats_software/WinVAM.htm

      King regards.

      Behrang.

      ----- Original Message -----
      From: "Edzer J. Pebesma"
      To: "Mach Nife"
      Cc: "ai-geostats"
      Sent: Tuesday, February 28, 2006 7:59 PM
      Subject: Re: [ai-geostats] Software for Automatic Semivariogram Estimation


      > Mach Nife wrote:
      >
      > >Hi,
      > >
      > >I'm hunting for a software (freeware/openSource if
      > >possible), that would help estimating the best
      > >possible semivariogram curve in a non-interactive way.
      > >As an example, ArcGis Geostatistical Analyst does a
      > >pretty good job at this when we accept the defaults.
      > >It does some automatic calculations for the parameters
      > >of the selected model. I've tried Gstat "Fit" method
      > >(in the command-line version), but the results aren't
      > >what I expected. What I need is a command line
      > >software or one that can be controlled by programming.
      > >
      > >Any ideas?
      > >
      > >
      >
      > Some. I did have a look at your data, and at the
      > ArcGIS fit window you sent me. Clearly, we do not
      > fully agree on what is to be considered a "good" job.
      > ArcGIS calculates semivariances up to the largest
      > distances present in your data set; afaik the general
      > recommendation is not to look further than half the
      > longest distance (compare acf computation in time
      > series); the gstat default is one third the diagonal
      > of the area spanned. Have you tried modifying any
      > of these defaults? Interval widths?
      >
      > When looking at the fit, it seems that ArcGIS shows
      > a couple (4?) directional variograms in a single
      > plot, but apart from that, the sample variogram suggests
      > a linear model. It is obvious that fitting three parameters
      > (exponential model with nugget) to something that
      > tends to be linear will lead to problems -- an infinite
      > set of solutions, for instance. When you insist on
      > having an exponential model, you could for
      > instance force the range to a certain (large) value.
      > I suspect ArcGIS stops adjusting the range of the
      > exponential model when it exceeds the data extent
      > (Constantin, are you with us?), but should that be
      > considered good practice?
      >
      > My experience with automatic, general-purpose
      > automatic variogram fitting are not very positive;
      > if it were, gstat would probably have such a function.
      >
      > Are there other ai-geostats readers who have positive or
      > negative experiences with, or who routinely trust,
      > automatically fitted variograms? Which software?
      >
      > Looking forward to a heated debate,
      > --
      > Edzer
      >
      > >machnife
      > >
      > >__________________________________________________
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      > >
      > >
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      >
      >


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