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AI-GEOSTATS: Re: VARIOWIN list of responses

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  • ivan ortiz valencia
    I am sending the answers I got. Many Thanks to Maria, Oliver, Peter and Ed. IVAN ivan, or you have too many data points (i don t think so) or you are using an
    Message 1 of 2 , Nov 11, 2003
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      I am sending the answers I got. Many Thanks to Maria, Oliver, Peter and


      or you have too many data points (i don't think so) or you are using an
      invalid format in the input data. it must
      be GEO-EAS format.
      if you have too many data points i did the following:
      used GAMV, program of GSLIB, and then transformed de output format to fit
      that of VARIOWIN (see chapter 6 of Yvan
      Pannatier's VARIOWIN Manual) saving the file with VAR extension and then
      modelling with MODEL of VARIOWIN.
      best regards,
      hi ivan, i once had the same problem......this is based in the fact that
      with 1500 points you've reached the maximal
      value of pairs that can be calculated by prevar 2d. try to minimise the
      maximum distances under setting or minimise
      your data set.........both worked fine for my data sets, which had an
      extent of almost 300 km (i minised the max
      distance to 15 km which was justifed from a technical point of view) and
      3000 ssampled locations.
      hope this helps,
      Oi Ivan,

      this has happened to me as well (I had 6810 points). Remember that there
      are n*(n-1)/2 pairs = 1,200,475 in your case. I succeeded to process a
      maximum of 1500 data points which produces a pcf file ca. 20 MB large.
      I tried 2 alternatives:

      1) Use the option "max. lag" of PREVAR which restricts the max. distance
      of data points such that the resulting number of pairs is < 1500 (or
      whatever your computer can handle; mine had 64 MB Ram, Win 98). But be
      careful: This makes sense only if you have an idea of the length scale of
      the structure you are investigating, because if you restrict the max.
      distance you can miss a structure.

      2) Select a random sub-sample out of your original data sample, comprising
      < 1500 points, and use this random sub-sample for analysis. Repeat this
      several times in order to see if the variogram is +- the same. I used a
      simple self-made program for producing a random sub-sample. This method
      has worked well in my case, using random sub-samples each comprising 20%
      of the total data set.

      Another idea: If you have Surfer-7, try the variogram utility of the grid
      menu. Maybe it can handle such large amounts of data. It is also somewhat
      easier to use than Variowin.
      good luck, pb


      May I suggest that you try SAGE2001 for all of your
      variogram calculations and modeling tasks.
      You will not have such problems with SAGE2001 and will
      find the modeling capabilities of SAGE2001 quite
      amazing. thanx, ed
      PS, go to www.isaaks.com to download the program.

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