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:[EMAIL PROTECTED]
Sent: 04 October 2005 08:45
To: AI Geostats mailing list
Subject: [ai-geostats] Unusual
Ordinary Kriging Results
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?
|
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
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