Michael Maybe we have not made this clear.
Universal kriging is a two stage process. (1) Fit a trend (global) or local trends and calculate the residuals. From these residuals you obtain a de-trended (drift-less) semi-variogram. (2) Using the semi-variogram derived in (1) together with the established form of the trend, you krige the complete value with trend from your original sample values -- not from the residuals. The only time you use the residuals is to get the semi-variogram model. People who refer to 'kriging with external drift' seem to mean different things and you would need to read each case on its own merits. I am sure there are people out there who can point you to the best references for that terminology. Try the kriging game together with our Wolfcamp tutorial which is freely available and distributable to anyone who wants it. Are we getting closer? Isobel Clark http://uk.geocities.com/drisobelclark/briefcase.html --- Michael Dennis <[EMAIL PROTECTED]> wrote: > Thanks for the info. I don't mind you plugging your > book, that was one of > the questions I asked : What is a good reference on > this subject. > > See this is where I start getting confused with > terminology. I'm talking > about KED (Kriging with External Drift) and then you > start talking about > Universal Kriging. If I understand correctly they > are not the same thing? > With Universal Kriging you remove the trend and Krig > the residuals but in > KED you use the trend(drift) in the actual krig > matrix? > > Mike > > -----Original Message----- > From: Isobel Clark > [mailto:[EMAIL PROTECTED]] > Sent: Thursday, December 06, 2001 11:18 AM > To: Michael Dennis > Cc: [EMAIL PROTECTED] > Subject: RE: AI-GEOSTATS: Kriging with External > Drift > > > > I'll see if I can get a > > copy of the book you mention to look at to see if > it > > helps me out. > > > > You say that KED uses a shape function for the > > "Drift" data. > 'shape functions' can be anything you like but most > people stick to simple polynomials. To use Univeral > Kriging the only constraint is that it has to be > expressed as a linear function in the coefficients. > That is: b0 + b1 * some function + b2 * some other > function and so on, where the b's are the > coefficients. > > All this is explained in detail in Chapter 12 of > Practical Geostatistics 2000, but we aren't allowed > to > say that on the open list ;-) > > You can try it out free (completely) with the > kriging > game in my briefcase. This shows you the equations > and > the terms calculated. A full tutorial on Universal > Kriging is also available in the briefcase and can > be > run with the free PG2000 software. > > Find them all at: > > http://uk.geocities.com/drisobelclark/briefcase.html > > Let us know if we can be of further help. > > Isobel Clark > > ________________________________________________________________ > Nokia 5510 looks weird sounds great. > Go to http://uk.promotions.yahoo.com/nokia/ discover > and win it! > The competition ends 16 th of December 2001. > > > -- > * To post a message to the list, send it to > [EMAIL PROTECTED] > * As a general service to the users, please remember > to post a summary of any useful responses to your > questions. > * To unsubscribe, send an email to [EMAIL PROTECTED] > with no subject and "unsubscribe ai-geostats" > followed by "end" on the next line in the message > body. DO NOT SEND Subscribe/Unsubscribe requests to > the list > * Support to the list is provided at http://www.ai-geostats.org ________________________________________________________________ Nokia 5510 looks weird sounds great. Go to http://uk.promotions.yahoo.com/nokia/ discover and win it! The competition ends 16 th of December 2001. -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
