Hi, Just to add to that Gotway and cressie I can't remember the exact citation did a large simulation study and showed that the bias from using the residual variogram is very small in most cases.
Nicholas On Fri, 7 Dec 2001 [EMAIL PROTECTED] wrote: > > On Friday, December 7, 2001, at 10:05 AM, Andreas Hartmann wrote: > > > > How do I compute the residual semivariogramm when I don't know the > > residuals? Or have I misunderstood something in the concept of external > > drift? > > There is a nice section (Chapter 5.4) in Cressie's textbook (Statistics > for > Spatial Data) that discusses the potential bias of estimating > semivariograms from residuals and Matheron's formulation of > IRF-K kriging as an alternative means to krige in the presence of > a trend. The iterative fitting of the covariance is usually > non-graphical, > which is a drawback in itself, and Fig. 5.1 in the same section shows > Cressie's bold attempt at showing the pitfalls of doing such an > "automatic" fit. I have not used IRF-K kriging very much in practice, > for the above reasons. Better to live with the devil that I know, i.e. > my -- albeit biased -- residual variogram. > > Regards, > > Syed > > > > -- > * 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 > CH3 | N Nicholas Lewin-Koh / \ Dept of Statistics N----C C==O Program in Ecology and Evolutionary Biology || || | Iowa State University || || | Ames, IA 50011 CH C N--CH3 http://www.public.iastate.edu/~nlewin \ / \ / [EMAIL PROTECTED] N C | || Currently CH3 O Graphics Lab School of Computing National University of Singapore The Real Part of Coffee [EMAIL PROTECTED] -- * 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
