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[ai-geostats] RE: Jacknifing in GSLIB and stubborn data points

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  • Norrie, Gordon
    Dear all, Thank you to all those who replied, your help was very much appreciated. As a result of that help I managed to get the result I wanted. I found
    Message 1 of 1 , Jul 23, 2004
      [ai-geostats] "Constrained" estimation / simulation
      Dear all,
      Thank you to all those who replied, your help was very much appreciated.  As a result of that help I managed to get the result I wanted.  I found that I was infact using too high a threshold of the minimum number of points in sparsely sampled areas that I was trying to Krige from.  Rather a silly error admittedly.
      Anyway, thanks again for all your help and suggestions. 
      Best regards,
      Gordon Norrie
      -----Original Message-----
      From: Norrie, Gordon
      Sent: 21 July 2004 21:24
      To: ai-geostats@...
      Subject: Jacknifing in GSLIB and stubborn data points

      Dear all,
      I've been trying to use the 'jacknifing' function in GSLIB, with Ordinary Kriging, with two data sets.  The first is a set of hard elevation points (numbering about 283) over an area of a river valley, taken by GPS.  The second is a set of 323 (approx) elevation points which are often very close to the hard elevation points, and whose values are unsampled and to which I'm trying to assign predicted elevations through the kriging process.  I've done the variogram modelling etc, but when it comes to applying the method it all works very well for predicting most of the 323 points, however, I am always left with a little clustered group of about 7 points which always give a value of -999 (which means 'unestimated').  I've tried tweaking and fiddling around a bit with the variogram model parameters, but all to no avail.  This stubborn select little clustered group refuse to be 'predicted' and remain 'unestimated'.  I can't see that their pattern is at all special, or that they are in anyway 'different' to other data which has kriged perfectly well.
      I am wondering if anyone might know or might have a hunch as to what is happening and what I should do to get these points to 'give in' and be estimated.
      Many thanks, in anticipation.
      Best regards,
      Gordon Norrie

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