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AI-GEOSTATS: analysis, interpretation, software questions

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  • Juliann Aukema
    Hello. I have several fairly basic questions about geostatistical analysis, interpretation and software. I received great advice from this list on a methods
    Message 1 of 1 , Feb 9, 2001
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      Hello. I have several fairly basic questions about geostatistical
      analysis, interpretation and software. I received great advice from this
      list on a methods question about a year ago (now I'm analyzing the data),
      so I thought I'd try the list on these questions. I've floundered through
      the archives, and some introductory books, but I'm still have some
      questions. I don't think it should be relevant for these questions, but
      just in case: I'm studying the ecology, distribution, dispersal of a
      parasitic plant and the data are on host characteristics, parasite
      prevalence etc. If you can help with even one of these questions (or
      correct any erroneous assumptions I have), I would appreciate hearing. I
      will summarize responses.

      1) In R (S plus clone), I can calculated trend surfaces and used
      the residuals to calculate detrended variograms or correlograms. In
      Geoeas and Variowin I can calculate directional (setting angels and
      tolerance) or omnidirectional variograms or correlograms.
      How does a detrended variogram compare to an omnidirectional or
      directional variogram? What are the pros and cons of these methods? (the
      variograms from the two methods look quite different, although the
      correlograms look quite similar)
      2) What exactly is the difference/ pros and cons of correlograms
      versus variograms? My correlograms look like almost pure nugget (except
      perhaps at very small lags), but the detrended variograms have interesting
      shapes - decreasing, upside down U, typical rise with plateau - how do I
      interpret this? Does one give me more information than the other?
      3) Where does kriging fit in? My understanding is that this is for
      prediction (and uses the variogram). I am mainly interested in description
      of patterns at this point.
      4) How do cross variograms work? I have variables that are
      correlated. Would cross variograms be appropriate?
      5) How does one determine an appropriate degree polynomial to use
      for trend surface analysis? Recommended reading for a beginner in trend
      6) Software: Is there a way in R to determine how many pairs are
      in each bin? Or to truncate variograms (it prints the entire distance and
      it is my understanding that one shouldn't calculate variograms beyond half
      the maximum distance).
      Can SAS do spatial statistics? Is it part of the basic
      package or is there some sort of add on? If you've tried it, do you
      recommend it?
      How do you make figures for publications? I like Geoeas and
      Variowin because I can see what they are doing and I can change parameters
      easily, but I have not been able to export figures. I find R frustrating
      because I don't feel like I can't see what it is doing (I'm a serious
      novice in R), but I can export the graphics. Any suggestions? (I don't have
      funds to buy software and I'm running out of time/patience for learning a
      lot of new software for this particular project).

      Thank you very much.

      Juliann Aukema

      Ecology and Evolutionary Biology
      University of Arizona
      Tucson, AZ 85721

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