Hi Tomislav, Don't be surprised. It is my experience that cross-validation might sometimes indicate that best interpolation results are obtained using the simplest techniques. If your observations are not too clustered and display no anisotropy, inverse square distance could yield good results. Now, you didn't explain which secondary information was used for cokriging and how many neighboring values were used in the different interpolators.
Regards, Pierre Goovaerts <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Dr. Pierre Goovaerts Consultant in (Geo)statistics 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 Fri, 15 Nov 2002, Tomislav Malvic RGNF wrote: > Dear all, > > > This is my first try at geostat mailing list, and maybe my question will not be very >"professional". > > > I work with data set of porosity in one oil reservoir. Interpolations were done with >three interpolation methods: Inverse distance weighting, Kriging (ordinary) and >Cokriging (collocated). I done spatial analysis with semivariogram modelling for >(co)Kriging. > > > After all, I calculated true error for every included point as difference between >real value and estimated value at the same place. I was confused when I saw that >Kriging error was higher of Inverse Distance Weighting error! The lowest errors were >gained by Cokriging (with the same semivariogram modell as used in Kriging). > > > What could be reason for that? Maybe 14 points is too low set for proper modelling >of directional semivariogram analysis (directions=0 and 90 degrees). I tested several >lag distances and distance with the highest range was chosen. If chosen distance is >too low interpolation map contains mostly areas of "bull-eyes". Also, input points >are moderately clustered. > > > Thank you and best regards, > > Tomislav > > -- * 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
