Gregoire, I believe I borrowed the term "large-scale" structure from the 1992 Gslib user's manual, note that the rodogram is not an option in the lastest release of Gslib. The terminology might be misleading since we mean features on the horizontal semivariogram axis (like range) as opposed to relative nugget effect which is inferred from the vertical axis of the semivariogram. This comment is purely empirical and is not backed up by any theory. Also I wouldn't draw any conclusion from a statistics computed on 9 observations.
Cheers, Pierre <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Dr. Pierre Goovaerts Consultant in (Geo)statistics President of PGeostat, LLC and Senior Chief Scientist with Biomedware Inc. 710 Ridgemont Lane Ann Arbor, Michigan, 48103-1535, U.S.A. E-mail: [EMAIL PROTECTED] Phone: (734) 668-9900 Fax: (734) 668-7788 http://alumni.engin.umich.edu/~goovaert/ <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> On Thu, 16 Jan 2003, Gregoire Dubois wrote: > Sorry for this re-posting, but a few signs have been improperly converted > in my text editor. Here it is again. > > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > To my question on the use of rodograms I got the two following references: > > Paul Harris gave me the following: > > Journel A. 1988. "New distance measures: the route toward truly non-gaussian > geostatistics", mathematical geology vol 20 no 4. > > Pierre Goovaerts mentioned at paper presented at the Geostat congress in > Avignon, 1988. > > Srivastava and Parker. 1989.Robust measures of spatial continuity. in M. > Armstrong, editor, Geostatistics, pages 295-308, Kluwer, Dordrecht. > > I will certainly have a look at these papers. On the basis of what I have > found so far, I still have a question about the use of rodograms. > > In Pierre's book, (page 31), the following is discussed: influence of > extreme values can be reduced by using lower values of the order of the > variogram (2 = traditional semivariogram, 1= madogram, 1/2= rodogram). On > page 86, it is further mentioned that relative rodograms and madograms provide > information (range, anisotropy) on large-scale features. This last point is > also mentioned in the manual of the GeostatOffice software "Rodograms and > madograms are useful for investigating large-scale structures, where data are > usually rather rough. If p=2 we get the most traditional measure called > variogram, it opens finer sides of data correlation and can fail for rough > data where rodogram and madogram succeed." (see > http://www.ibrae.ac.ru/+AH4-mkanev/eng/gsoffice/HELP/Appendix.html) > > My original question on rodogram came from a micro scale analysis of 9 points > located very closely (measurements of radioactivity made on a grid with nodes > separated by 12 cm). The fact that only the rodogram revealed a clear spatial > structure (unless you do an audacious regression of the experimental > semivariogram) might be an artefact due to the very few samples or a correct > approach if it wouldn't contradict the theory claiming that rodograms are more > useful for large-scale structures. > > Is this argumentation based on theory or on experience with environmental > data? > > I would appreciate your feedback about this last point. > > Gregoire > > (Has everyone made a new-year resolution on contributing to AI-GEOSTATS ?? > The activity of the mailing list has been boosted tremendously since the > beginning of this year). > > > > > -- > * 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 > -- * 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
