Dear Prof. Clark
Here is thepaper:
http://www.ansinet.org/fulltext/jas/jas581405-1407.pdf
Formula (4) is the weight factor.
King regards.
Behrang.
- Original Message -
From:
Isobel Clark
To: Behrang Kushavand
Cc: AI Geostats mailing list
Sent: Tuesday, February 28, 2006 9:53
PM
Subject: [ai-geostats] Re: Software for
Automatic Semivariogram Estimation
Behrang
What weighting do you use in the weighted least squares?
Isobel
http://www.kriging.comBehrang
Kushavand [EMAIL PROTECTED]
wrote:
hi,I
have a software for Variogram AUTO Modeling (winvam) that works with
gslib(GAMV.exe).First you must calculate experimental variogram
(omni or directional) withgamv.exe and then by using winvam, you can fit
the best model by leastsquare and weights least square criteria for
given model(s),You can find it
at:http://www.ai-geostats.org/software/Geostats_software/WinVAM.htmKing
regards.Behrang.- Original Message -From: "Edzer
J. Pebesma" <[EMAIL PROTECTED]>To: "Mach Nife"
<[EMAIL PROTECTED]>Cc: "ai-geostats" <AI-GEOSTATS@UNIL.CH>Sent:
Tuesday, February 28, 2006 7:59 PMSubject: Re: [ai-geostats] Software
for Automatic Semivariogram Estimation Mach Nife
wrote: 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? Some.
I did have a look at your data, and at the ArcGIS fit window you
sent me. Clearly, we do not fully agree on what is to be considered
a "good" job. ArcGIS calculates semivariances up to the
largest distances present in your data set; afaik the
general recommendation is not to look further than half the
longest distance (compare acf computation in time series); the gstat
default is one third the diagonal of the area spanned. Have you
tried modifying any of these defaults? Interval
widths? When looking at the fit, it seems that ArcGIS
shows a couple (4?) directional variograms in a single plot,
but apart from that, the sample variogram suggests a linear model.
It is obvious that fitting three parameters (exponential model with
nugget) to something that tends to be linear will lead to problems
-- an infinite set of solutions, for instance. When you insist
on having an exponential model, you could for instance force
the range to a certain (large) value. I suspect ArcGIS stops
adjusting the range of the exponential model when it exceeds the
data extent (Constantin, are you with us?), but should that
be considered good practice? My experience with
automatic, general-purpose automatic variogram fitting are not very
positive; if it were, gstat would probably have such a
function. Are there other ai-geostats readers who have
positive or negative experiences with, or who routinely
trust, automatically fitted variograms? Which
software? Looking forward to a heated debate,
-- Edzer machnife
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