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[ai-geostats] Unusual Ordinary Kriging Results

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  • Reid, David W
    Hello, After running ordinary kriging estimations using Vulcan mine planning software it was noticed there were some unusual estimated grades. I was hoping
    Message 1 of 4 , Oct 4, 2005
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      Hello,
       
      After running ordinary kriging estimations using Vulcan mine planning software it was noticed there were some unusual estimated grades. I was hoping that someone can confirm that I on the right path + not heading up the yellow brick road to Oz.
       
      The estimated value reported/calculated by Vulcan for one block was 80.77.  I thought this unusual as the grade of the 16 samples selected for the estimation range from 51.2 to 65.9 (mean 59.6).   I calculated the estimated grade by summing the products of sample grade and sample weight (given by the software) and got a value of 60.13 which seems far more reasonable.
       
      Maptek the software vendor's response was to suggest that negative weights were responsible for the high estimation.
       
      Details of the samples are below.
       
      Have I overlooked something in my calculation or is there some other explanation for the result?
       
      Regards
       
      David Reid
       
      NumberXYZGradeDistanceweightweight * grade
      151325.619954.3205.28648.7550.31681120.27589
      251325.619954.3206.86412.7510.0475553.043512
      35131019953.7206.9565.915.6990.0970726.397071
      451308.219968.6206.5851.219.1830.0785374.021086
      551309.419970.1206.6763.919.5570.058283.724066
      651325.319939205.0858.219.9480.084324.907436
      75131019939.3204.7855.121.1970.1173516.466049
      851325.319977.5204.9856.721.2670.18251110.34838
      951310.319938.7204.886021.6460.0859065.154343
      1051325.319939206.658.221.843-0.03607-2.09928
      115131019939.3206.355.40522.767-0.00408-0.22581
      1251325.319977.5206.556.722.980.0281311.59505
      1351310.319938.7206.46023.259-0.02124-1.27434
      1451309.419970.1208.962.324.395-0.0517-3.22108
      1551340.219939205.486128.1720.0408172.489816
      1651340.2199392076129.772-0.0242-1.4764
      TOTAL160.12579
      Ave59.60031block estimate 80.77
       
       
       

      David Reid

      This message and any attached files may contain information that is confidential and/or subject of legal privilege intended only for use by the intended recipient. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, be advised that you have received this message in error and that any dissemination, copying or use of this message or attachment is strictly forbidden, as is the disclosure of the information therein. If you have received this message in error please notify the sender immediately and delete the message.
    • Mario Rossi
      David, I assume you ve checked for the little things that may be silly mistakes, such as comparing the same blocks; or making sure that the estimation
      Message 2 of 4 , Oct 4, 2005
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        David,
         
        I assume you've checked for the "little things" that may be silly mistakes, such as comparing the same blocks; or making sure that the estimation parameter files are reading the intended variables.
         
        If all the above checks, then it's possible that there is "bug", and that can be in different forms; for instance, incompatability between parameters and files setup in a version, and trying to use them in a newer version (are you trying out V6.0?).
        Then again, it could be a true bug,  an error in the programming; however, I think this is less likely if you're using the OK program implemented from GSLIB within Vulcan; it has been thoroughly checked and debugged for a number of years (and versions, since 3.5 at least).
         
        Clearly, it's not the negative weights...
         
        Good luck!
         
        Cheers,
         
         
        Mario
         
        PD: It looks to me like you're dealing with Fe ore; hematite? If you truly happen to have a 80.X value in a block, let me know! I'll fly out there (to WA?) to witness the miracle...


        "Reid, David W" <David.W.Reid@...> wrote:
        Hello,
         
        After running ordinary kriging estimations using Vulcan mine planning software it was noticed there were some unusual estimated grades. I was hoping that someone can confirm that I on the right path + not heading up the yellow brick road to Oz.
         
        The estimated value reported/calculated by Vulcan for one block was 80.77.  I thought this unusual as the grade of the 16 samples selected for the estimation range from 51.2 to 65.9 (mean 59.6).   I calculated the estimated grade by summing the products of sample grade and sample weight (given by the software) and got a value of 60.13 which seems far more reasonable.
         
        Maptek the software vendor's response was to suggest that negative weights were responsible for the high estimation.
         
        Details of the samples are below.
         
        Have I overlooked something in my calculation or is there some other explanation for the result?
         
        Regards
         
        David Reid
         
        NumberXYZGradeDistanceweightweight * grade
        151325.619954.3205.28648.7550.31681120.27589
        251325.619954.3206.86412.7510.0475553.043512
        35131019953.7206.9565.915.6990.0970726.397071
        451308.219968.6206.5851.219.1830.0785374.021086
        551309.419970.1206.6763.919.5570.058283.724066
        651325.319939205.0858.219.9480.084324.907436
        75131019939.3204.7855.121.1970.1173516.466049
        851325.319977.5204.9856.721.2670.18251110.34838
        951310.319938.7204.886021.6460.0859065.154343
        1051325.319939206.658.221.843-0.03607-2.09928
        115131019939.3206.355.40522.767-0.00408-0.22581
        1251325.319977.5206.556.722.980.0281311.59505
        1351310.319938.7206.46023.259-0.02124-1.27434
        1451309.419970.1208.962.324.395-0.0517-3.22108
        1551340.219939205.486128.1720.0408172.489816
        1651340.2199392076129.772-0.0242-1.4764
        TOTAL160.12579
        Ave59.60031block estimate 80.77
         
         
         

        David Reid

        This message and any attached files may contain information that is confidential and/or subject of legal privilege intended only for use by the intended recipient. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, be advised that you have received this message in error and that any dissemination, copying or use of this message or attachment is strictly forbidden, as is the disclosure of the information therein. If you have received this message in error please notify the sender immediately and delete the message.
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        GeoSystems International
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      • Reid, David W
        Thank you for you replies. Especially Bruce Ramsey for putting me on the right path. It turned out to be something that I was overlooking. The estimation run
        Message 3 of 4 , Oct 4, 2005
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          Thank you for you replies. Especially Bruce Ramsey for putting me on the right path.
           
          It turned out to be something that I was overlooking.   The estimation run had the "variable weighting" option selected and the composite length was selected as the weighting.  I had taken the weights from a report window, these were not the weights used in the estimation. The actual weights applied to estimate the grade are the (length) applied weights which are located in a "explain" text file.  The estimate is correct given the input data, but not reasonable! (80% fe in hematite is a miracle).
           
          Variable 1 of 1: input='FE' output='fe'    variable weighting
             Value     Weight  variable Applied weight
            64.000    0.317    0.048    0.015
            64.000    0.048    3.000    0.143
            65.900    0.097    1.107    0.107
            51.200    0.079    0.037    0.003
            63.900    0.058    1.467    0.085
            58.200    0.084    0.048    0.004
            55.100    0.117    0.048    0.006
            56.700    0.183    0.048    0.009
            60.000    0.086    0.048    0.004
            58.200   -0.036    3.000   -0.108
            55.405   -0.004    3.000   -0.012
            56.700    0.028    3.000    0.084
            60.000   -0.021    3.000   -0.064
            62.300   -0.052    3.000   -0.155
            61.000    0.041    0.048    0.002
            61.000   -0.024    3.000   -0.073
             #samples=16, total weight=0.050778 estimate=80.769272
          In the case of this block there were some very short composites (0.048m) that should have been excluded from the estimation.  Once length weighting is turned off (or short composites are excluded)  the estimation result is reasonable. 
           
          It appears that the length weighting is amplifying the effect of the negative weights.
           
          We try and use a sample search that minimises occurrence of negative weights, but this is often a compromise with variable sample density + orientation.  It would be nice to be able to estimate with a  search optimised  for each block.  Negative weights are usually more of a problem with less well behaved elements like P (mitigated somewhat by higher nugget variograms).
           
          Thanks again for your help, I will be able to rest easily at night knowing Vulcan has been producing correct estimates.
           
          Regards 
           
          David Reid
          -----Original Message-----
          From: Reid, David W [mailto:David.W.Reid@...]
          Sent: Tuesday, 4 October 2005 4:45 PM
          To: AI Geostats mailing list
          Subject: [ai-geostats] Unusual Ordinary Kriging Results

          Hello,
           
          After running ordinary kriging estimations using Vulcan mine planning software it was noticed there were some unusual estimated grades. I was hoping that someone can confirm that I on the right path + not heading up the yellow brick road to Oz.
           
          The estimated value reported/calculated by Vulcan for one block was 80.77.  I thought this unusual as the grade of the 16 samples selected for the estimation range from 51.2 to 65.9 (mean 59.6).   I calculated the estimated grade by summing the products of sample grade and sample weight (given by the software) and got a value of 60.13 which seems far more reasonable.
           
          Maptek the software vendor's response was to suggest that negative weights were responsible for the high estimation.
           
          Details of the samples are below.
           
          Have I overlooked something in my calculation or is there some other explanation for the result?
           
          Regards
           
          David Reid
           
          NumberXYZGradeDistanceweightweight * grade
          151325.619954.3205.28648.7550.31681120.27589
          251325.619954.3206.86412.7510.0475553.043512
          35131019953.7206.9565.915.6990.0970726.397071
          451308.219968.6206.5851.219.1830.0785374.021086
          551309.419970.1206.6763.919.5570.058283.724066
          651325.319939205.0858.219.9480.084324.907436
          75131019939.3204.7855.121.1970.1173516.466049
          851325.319977.5204.9856.721.2670.18251110.34838
          951310.319938.7204.886021.6460.0859065.154343
          1051325.319939206.658.221.843-0.03607-2.09928
          115131019939.3206.355.40522.767-0.00408-0.22581
          1251325.319977.5206.556.722.980.0281311.59505
          1351310.319938.7206.46023.259-0.02124-1.27434
          1451309.419970.1208.962.324.395-0.0517-3.22108
          1551340.219939205.486128.1720.0408172.489816
          1651340.2199392076129.772-0.0242-1.4764
          TOTAL160.12579
          Ave59.60031block estimate 80.77
           
           
           

          David Reid

          This message and any attached files may contain information that is confidential and/or subject of legal privilege intended only for use by the intended recipient. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, be advised that you have received this message in error and that any dissemination, copying or use of this message or attachment is strictly forbidden, as is the disclosure of the information therein. If you have received this message in error please notify the sender immediately and delete the message.
          This message and any attached files may contain information that is confidential and/or subject of legal privilege intended only for use by the intended recipient. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, be advised that you have received this message in error and that any dissemination, copying or use of this message or attachment is strictly forbidden, as is the disclosure of the information therein. If you have received this message in error please notify the sender immediately and delete the message.
        • Colin Badenhorst
          Hi David, Wow. I don t think the problem is the negative weights. Which version are you using at the moment? Are you using tetramodelling by any chance? I
          Message 4 of 4 , Oct 5, 2005
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            Hi David,

             

            Wow. I don’t think the problem is the negative weights. Which version are you using at the moment? Are you using tetramodelling by any chance?

             

            I presume you generated the result below using the BEF Explain menu option, is that correct?

             

            Regards,

            Colin

             


            From: Reid, David W [mailto:David.W.Reid@...]
            Sent: 04 October 2005 08:45
            To: AI Geostats mailing list
            Subject: [ai-geostats] Unusual Ordinary Kriging Results

             

            Hello,

             

            After running ordinary kriging estimations using Vulcan mine planning software it was noticed there were some unusual estimated grades. I was hoping that someone can confirm that I on the right path + not heading up the yellow brick road to Oz.

             

            The estimated value reported/calculated by Vulcan for one block was 80.77.  I thought this unusual as the grade of the 16 samples selected for the estimation range from 51.2 to 65.9 (mean 59.6).   I calculated the estimated grade by summing the products of sample grade and sample weight (given by the software) and got a value of 60.13 which seems far more reasonable.

             

            Maptek the software vendor's response was to suggest that negative weights were responsible for the high estimation.

             

            Details of the samples are below.

             

            Have I overlooked something in my calculation or is there some other explanation for the result?

             

            Regards

             

            David Reid

             

            Number

            X

            Y

            Z

            Grade

            Distance

            weight

            weight * grade

            1

            51325.6

            19954.3

            205.28

            64

            8.755

            0.316811

            20.27589

            2

            51325.6

            19954.3

            206.8

            64

            12.751

            0.047555

            3.043512

            3

            51310

            19953.7

            206.95

            65.9

            15.699

            0.097072

            6.397071

            4

            51308.2

            19968.6

            206.58

            51.2

            19.183

            0.078537

            4.021086

            5

            51309.4

            19970.1

            206.67

            63.9

            19.557

            0.05828

            3.724066

            6

            51325.3

            19939

            205.08

            58.2

            19.948

            0.08432

            4.907436

            7

            51310

            19939.3

            204.78

            55.1

            21.197

            0.117351

            6.466049

            8

            51325.3

            19977.5

            204.98

            56.7

            21.267

            0.182511

            10.34838

            9

            51310.3

            19938.7

            204.88

            60

            21.646

            0.085906

            5.154343

            10

            51325.3

            19939

            206.6

            58.2

            21.843

            -0.03607

            -2.09928

            11

            51310

            19939.3

            206.3

            55.405

            22.767

            -0.00408

            -0.22581

            12

            51325.3

            19977.5

            206.5

            56.7

            22.98

            0.028131

            1.59505

            13

            51310.3

            19938.7

            206.4

            60

            23.259

            -0.02124

            -1.27434

            14

            51309.4

            19970.1

            208.9

            62.3

            24.395

            -0.0517

            -3.22108

            15

            51340.2

            19939

            205.48

            61

            28.172

            0.040817

            2.489816

            16

            51340.2

            19939

            207

            61

            29.772

            -0.0242

            -1.4764

            TOTAL

             

             

             

             

             

            1

            60.12579

             

             

             

            Ave

            59.60031

             

            block estimate

            80.77

             

             

             

            David Reid

            This message and any attached files may contain information that is confidential and/or subject of legal privilege intended only for use by the intended recipient. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, be advised that you have received this message in error and that any dissemination, copying or use of this message or attachment is strictly forbidden, as is the disclosure of the information therein. If you have received this message in error please notify the sender immediately and delete the message.
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