Hello, I have been using a modified version of VARFIT that is available on the Computer and Geosciences website. Pardo-Iguzquiza E: VARFIT: a Fortran-77 program for fitting variogram models by weighted least squares. Computers and Geosciences 1999, 25:251-261. I agree that choosing a set of weighting factors for the fit can be frustrating and it's why in the program I provided with my latest IJHG paper, I allowed the user to choose among 5 options for the weights. For the weights N(h)/gamma(h), I used the experimental semivariogram values, which eliminates the problem of weights that change during the iterative fitting procedure and also attenuates the impact of unreliable semivariogram values computed for the first lags (i.e. impact of preferential sampling of high values as in my WRR paper on groundwater arsenic concentrations). I have increasingly used automatic fitting procedures, followed by a visual assessment of the fit (and yes the fitting of variogram clouds in Arcview is one of the many ESRI blunders). It has proven convenient in several situations: 1. implementation of Poisson kriging to be used by epidemiologists, who have no idea what a semivariogram is, for removing noise from rate data, 2. use of indicator kriging for automatic mapping procedures (SIC 2004 paper that is available on my webpage). 3. testing of new algorithms using hundreds of simulations. The common use of only one jackknife or simulation to compare the prediction performances of various algorithms is very hazardous since the ranking can drastically change would another subset of data be used for validation. Cheers, Pierre Pierre Goovaerts Chief Scientist at BioMedware 516 North State Street Ann Arbor, MI 48104 Voice: (734) 913-1098 (ext. 8) Fax: (734) 913-2201 http://home.comcast.net/~goovaerts/
________________________________ From: Mach Nife [mailto:[EMAIL PROTECTED] Sent: Tue 2/28/2006 10:16 AM To: ai-geostats Subject: [ai-geostats] Software for Automatic Semivariogram Estimation Hi, I'm hunting for a software (freeware/openSource if possible), that would help estimating the best possible semivariogram curve in a non-interactive way. As an example, ArcGis Geostatistical Analyst does a pretty good job at this when we accept the defaults. It does some automatic calculations for the parameters of the selected model. I've tried Gstat "Fit" method (in the command-line version), but the results aren't what I expected. What I need is a command line software or one that can be controlled by programming. Any ideas? machnife __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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