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Many thanks. You are absolutely correct. SAS took more than 8 hours in computing 5000 points, while Arcgis only took several seconds. By the way, I still cannot find this book 'Cressie (1993)' in China. Could you send me relative equations? My email address: caroline_qi@163.com Best regards
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09-23-2011
02:06 AM
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I compared the performance of geostatistical models to estimate average temperature in each month using weather station temperature and elevation. Monthly estimates were validated for 30% split-sample of stations with ordinary cokriging in ArcGIS and universal kriging in SAS Proc Mixed. They were produced with elevation as a covariate using ordinary cokriging in ArcGIS and universal kriging in SAS. Performance of models was assessed by comparing adjusted R2, mean squared error, root mean squared error. Accuracy and precision were higher for universal kriging estimates in SAS. In arcgis, I use Histograms, Normal QQ Plots and trend analyses and select the proper parameter to do the cokriging. But in SAS, there are not many parameters needed to be adjusted. For what I know is that SAS uses the restricted maximum likelihood method to estimate variance and covariance of the models and Arcgis builds semivariograms and computs corresponding semivariogram parameters. I select exponencial model in both Arcgis and SAS. I use split validation not cross validation.
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09-21-2011
04:44 PM
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Could someone tell me what is the Arcgis cokriging equation? I can only find the simple equation which is: Z1(s) = µ1 + ε1(s) Z2(s) = µ2 + ε2(s) When I use SAS to do the cokriging analysis, it's more accurate than using Arcgis. So I want to compare the difference between each equation. Many thanks, Xiaopeng
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09-21-2011
05:13 AM
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I use monthly station temperature and elevation to interpolate U.S. national temperature. I want to create prediction map with Ordinary kriging. After the trend removal, I need to select the model of semivariagram. I find the cross-validation is better if I choose model 1(Exponential) + model 2(Exponetial) than only selecting model 1 (Exponential). What that means? Does it make sense if the the two models are same? I'm still confused about the model1, model 2 and model3. I cannot find some exact exmple for multi-model selecton. Look forward to your response. Thanks, Xiaopeng
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11-08-2010
04:53 AM
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