you will find a few codes for Surfer. I have just added
crossvalidation.bas , a code I derived from Aleksey Amantov's
You will need to code a bit yourself to select the correct interpolation
function (Inverse Distance Weighted is the default) as well as the
proper parameters. Surfers manual is sufficient to learn to program with
Scripter (quick basic). Sorry, but I will not provide any support. Note
that crossvalidations are implemented in Surfer 8.
2) In short: Geostatistics are not appropriate when you don't have a
spatial correlation (even this is questionable :) ).
Frequently, people who do not find any spatial correlation in their data
apply other functions like Inverse Weighted Distance. I believe such a
solution is completelt wrong. Either you have a spatial correlation and
you can interpolate/predict values, or you don't and only models based
on sound physics (e.g. Temperature T decreases with latitude and
altitude, thus you can predict T) can be used. Outside of these two
solutions, I would recommend only to use Thiessen polygons for
displaying purposes (not for real estimations!): they do not look
"natural" when applied to continuous variables and can thus not fool the
persoon looking at the output. Moreover, Thiessen polygons provides
useful information on the weight of each sample. Maps of proportional
symbols would also do.
From: Mark Dowdall [mailto:mark.dowdall@...
Sent: 01 September 2004 10:02
Subject: [ai-geostats] XValid script
It may be cheeky, but I have two questions:
1. Where can I get I get the Surfer v7.0 script for crossvalidation? I
have been through the archives and although its mentioned I cannot find
a download site. Nor could I find it and the site of Aleksey Amantov.
Some emails mentioned it is in the samples folder of the surfer install
but I could not find it. I know its in Surfer 8 as standard but thats
not available to me at the moment.
2. I have been following the discussion on extreme values in a data set.
And my question is: is there any context in which geostatistical methods
are absolutely not appropriate? If so, how can this appropriateness be
tested? Is there a point at which a user should know that it would be
better to try something else?
Any help with these two is very much welcome