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GEOSTATS: thanks for help on kriging problem

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  • ejwexler
    Dear List Members: Thanks to all for the very rapid response for aid in finding a simple kriging program to verify a VB5 gridding and variance analysis code
    Message 1 of 1 , Oct 21 11:37 PM
      Dear List Members:

      Thanks to all for the very rapid response for aid in finding a simple
      kriging program to verify a VB5 gridding and variance analysis code I've
      been working on.

      Several people recommended GSLIB. I downloaded, compiled, and ran Ktb3d
      with no problems. GSLIB gave the same results as mine for the example
      problem in Isaaks and Srivastava ehich used an exponential variogram
      with a 50% sill. The results did differ from the values posted on
      Figure 12.10 in I&S. Other programs recommended included GS+
      (www.gammadesign.com) and gstat (www.geog.uu.nl/gstat/). I haven't had
      a chance to try them yet.

      Many thanks also to Donald Meyers from the U. of Arizona for his timely
      answer to problems with the Gaussian variogram. As a final check on my
      program, I was testing the topographic data set in Davis (1973). The
      problem worked fine for all variograms except the gaussian which gave
      complete garbage. Rather than spending hours trying to find a
      non-existant bug, adding a small nugget cured the problem. Further
      testing showed that a nugget as small as 6.5 (0.1%) worked with a sill
      of 6500. The gaussian variogram also gave reasonable results without a
      nugget for universal kriging with a linear or quadratic drift but then
      the sill values were much lower (850 for the quadratic). I'll have to
      look further into this ill-conditioned matrix problem.

      E.J. Wexler
      ejwexler@...
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