2428RE: [ai-geostats] Software for Automatic Semivariogram Estimation
- Feb 28, 2006Hello,
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.
Chief Scientist at BioMedware
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From: Mach Nife [mailto:machnife@...]
Sent: Tue 2/28/2006 10:16 AM
Subject: [ai-geostats] Software for Automatic Semivariogram Estimation
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.
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