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Re: GEOSTATS: interpolation

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  • Donald Myers
    Tha is a non-sequitur, given only a finite amount of data and no state equations you have a non-unique problem. First of all one has to ask what does best
    Message 1 of 4 , Apr 1, 1998
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      Tha is a non-sequitur, given only a finite amount of data and no state
      equations you have a non-unique problem. First of all one has to ask what
      does "best" mean? Again this is non-unique.

      There are quite a number of papers that have compared different
      methods/algorithms/implementations of algorithms/applications of algorithms
      for rainfall and temperature data but in general one can only conclude that
      for a particular data set one method or algorithm seemed to work best.

      You mentioned using arcview spatial software and inverse distance weighting
      with a specific choice of the search neighborhood. The results can be
      sensitive to not only the choice of the search neighborhood but also the
      choice of the exponent. See for example, Kane et al, Computers and
      Geosciences, 1982.

      If one uses kriging, i.e., a variant of kriging (simple, ordinary,
      universal, indicator, etc) then one still has to estimate and model the
      variogram as well as to choose the search neighborhood parameters. Unless
      the elevation is approximately constant over your region of interest you
      may need to incorporate that effect either by cokriging or by using an
      external drift.

      Differences in results from using different methods/algorithms may be
      considerably affected (or not) by the pattern of data locations.

      Do you want point interpolations or do you want average rainfall over
      specific subregions? Kriging will allow you to directly do the latter but
      IWD does not.

      Note that the thin plate spline and smoothing spline are both special cases
      of kriging.

      My suggestion is to search the literature more completely for papers that
      have applied different methods and try to match the specifics of one of
      those instances to your problem.

      Donald Myers
      Department of Mathematics
      University of Arizona
      Tucson, AZ 85721

      http://www.u.arizona.edu/~donaldm

      At 12:24 PM 4/1/98 +0000, you wrote:
      >hi
      >
      >i would like to find out the best method for interpolating rainfall
      >and temperature data. the weather stations are randomly spread over
      >an area of approx. 8 million hectares. there are approx. 200 temp
      >stations and approx 1000 rainfall stations. i have tried inverse
      >distance weighting with 4 nearest neighbours for temp and 8 for
      >rainfall, both using a 300m grid size. i am using arcview spatial
      >analyst software.
      >
      >any help is appreciated.
      >craig email: c_vhagen@...
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    • Yoshiro Nagao
      I have a few questions on ArcView Spatial Analyst. (Sorry for not answering to your question.) ... Can ArcView Spatial output interpolated values for several
      Message 2 of 4 , Apr 1, 1998
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        I have a few questions on ArcView Spatial Analyst.
        (Sorry for not answering to your question.)

        c_vhagen@... sama said:
        >rainfall, both using a 300m grid size. i am using arcview spatial
        >analyst software.

        Can ArcView Spatial output interpolated values for
        several points which are listed in a table.

        I mean,

        You specify points for which you want interpolated values as follows:

        long. lat.
        8.5 135.2
        9.2 135.7
        10.3 136.0


        Then ArcView Spatial would output interpolated values to the above points
        into a file:

        long. lat. interpolated value
        8.5 135.2 23
        9.2 135.7 24
        10.3 136.0 25

        Or do you need to click each the above points on the map to see the interpolated
        values?

        How about other interpolation softwares?

        Nagao Yoshiro
        International Centre for Medical Research
        Kobe University
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