Hi Perry, I am curious to see how others will reply to your second question on the difference between a dataset with a trend and one that is non-stationary! My reply may sound provocative: you can always remove a trend when you recognize that there is one. Moving from non-stationarity to stationarity, on the other hand, can be infinitely more complex (e.g. moving to non-Euclidean space)
:) For what concerns the detection of trends, have a look at the variogram: a quadratic/exp. increase usually means that there is a trend. Get rid of the presumed trend and check the variogram of the residuals which should clearly show a change of structure (if you had a trend obviously). Quicker might be to use a moving windows strategy to plot local averages and check if you see any structure (be careful that the "structure" is not simply an anisotropy of your variable). You could have a look into the old archives of AI-GEOSTATS. There have been very nice replies from Donald Myers (see his publications) in the past on these issues. see http://groups.yahoo.com/group/ai-geostats/ Regards GD -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: 07 July 2005 03:49 To: [email protected] Subject: RE: [ai-geostats] modelling trend and kriging type Hi all I may know this already, but what are the symptoms of data with a trend? What is the difference between a dataset with a trend and a non-stationary dataset? Cheers Perry Collier Senior Mine Geologist Ernest Henry Mine Xstrata Copper Australia Ph (07) 4769 4527 Fx (07) 4769 4555 E-mail [EMAIL PROTECTED] Web http://www.xstrata.com PO Box 527 Cloncurry QLD 4824 Australia "Light travels faster than sound. That is why some people appear bright until you hear them speak" -----Original Message----- From: Pierre Goovaerts [mailto:[EMAIL PROTECTED] Sent: Friday, 1 July 2005 12:54 AM To: Recep kantarci; [email protected] Subject: RE: [ai-geostats] modelling trend and kriging type To add to the excellent comments by Edzer and Gregoire, 1. Universal kriging = kriging with a trend. The second terminology has been proposed by Andre Journel who felt that the term "universal" was vague and misleadingly "ambitious". 2. Kriging with an external drift (KED) is mathematically the same as universal kriging (UK). Secondary variables are simply replacing the spatial coordinates used in UK. 3. Regression kriging denotes all the techniques where the trend is modeled outside the kriging algorithm. There are various methods that can be used to model that trend, ranging from linear regression to neural networks. Kriging is used to interpolate the residuals. In practice these techniques have more flexibility than universal kriging in term of modeling the trend: multiple variables either categorical or continuous can be incorporated easily and many sofwtare are available for this trend modeling. The only limitation is that the trend is modeled globally (i.e. the regression coefficients are constant in space) while in KED the coefficients are reestimated within each search window. Cheers, Pierre Pierre Goovaerts Chief Scientist at Biomedware 516 North State Street Ann Arbor, MI 48104 Voice: (734) 913-1098 Fax: (734) 913-2201 http://home.comcast.net/~goovaerts/ -----Original Message----- From: Recep kantarci [mailto:[EMAIL PROTECTED] Sent: Thu 6/30/2005 9:38 AM To: [email protected] Cc: Subject: [ai-geostats] modelling trend and kriging type Dear ai-geostats members When the data used has a trend, it is needed to model trend and in this case there exists various types of kriging to apply (universal kriging, kriging with a trend, regression kriging etc). If this is the case, does one should use the same type of kriging or different depending on modeling the trend using coordinates of target variable or using other (namely, secondary or auxillary) variables such as elevation or topography ? That is , are there a dinstinction depending on the type of variables to model the trend while kriging? Best regards Recep _____ Yahoo! kullaniyor musunuz? Istenmeyen postadan biktiniz mi? Istenmeyen postadan en iyi korunma Yahoo! Posta'da http://tr.mail.yahoo.com <http://tr.mail.yahoo.com/> ********************************************************************** The information contained in this e-mail is confidential and is intended only for the use of the addressee(s). If you receive this e-mail in error, any use, distribution or copying of this e-mail is not permitted. You are requested to forward unwanted e-mail and address any problems to the Xstrata Queensland Support Centre. Support Centre e-mail: [EMAIL PROTECTED] Support Centre phone: Australia 1800 500 646 International +61 2 9034 3710 **********************************************************************
* By using the ai-geostats mailing list you agree to follow its rules ( see http://www.ai-geostats.org/help_ai-geostats.htm ) * To unsubscribe to ai-geostats, send the following in the subject or in the body (plain text format) of an email message to [EMAIL PROTECTED] Signoff ai-geostats
