What does the software update resolve?
Leapfrog Edge 4.0.5 resolves an issue affecting the calculation of the experimental variogram in the minor axis direction.
This issue affects versions back to Leapfrog Edge 2.3 (Leapfrog Geo 4.3 installer released in June 2018).
In what use cases may the issue occur?
The issue presents in cases where the major axis dips in a westerly direction (where the ‘dip azimuth’ of the directions panel is in the range 181->359°). In this situation, the azimuth of the minor axis vector is mistakenly reversed, resulting in incorrect pairs being selected for the minor axis experimental variogram. The incorrect vector direction being used is illustrated in the diagram below.
The difference between the expected minor axis direction and the reversed direction is dependent on the dip. The effect is small at shallow or steep dips, and largest for moderate dips, as illustrated.
Note: Variograms with an eastward dip (dip azimuth 0->180) are not affected.
What potential impacts may arise?
This issue outlined above ONLY affects the calculation of the minor axis experimental variogram. The experimental variograms are used as a guide for a user’s ‘choice’ of variogram model parameters (type/sills/ranges). The issue may lead a user to fit an inappropriate model range in the minor axis direction.
The effect this may have on resource models and/or resource estimates is unpredictable and depends on multiple factors, including:
- The orientation of data
- Geometry of domain
- Search strategy used Cut-off grade and relationship to mean grade.
In general, the search strategy employed will exert a stronger influence on estimated values than the variogram does, particularly for narrower domains, but the effect of changing the variogram ranges in the minor direction should be assessed.
Note that this issue has NO effect on variable orientation.
- If there is no VO used, the variogram model will be used with the rotations defined in the ‘directions panel’
- If VO is used, then the variogram model (and the search) get re-orientated to match the local orientation. But the model RANGEs are NOT changed. It does not matter what the local VO orientation is – this can dip anywhere.
What can I do to assess whether my Edge estimate may be affected?
1. Assess existing model fit using a custom variogram (in an existing Geo/Edge project)
You can utilize a ‘custom variogram’ oriented in the true minor axis direction to replicate the minor axis experimental variogram. This will show how well the existing variogram model fits in the minor axis direction and can be done in an existing Geo/Edge project.
The custom variogram should have the same plunge as the label on the minor axis, with 180 degrees subtracted from the trend.
For example, if the minor axis is labelled 65-> 292, enter 65 and 112 (=292-180) as the plunge and trend of the custom variogram. Ensure that you use a lag distance appropriate to the sample spacing in the minor axis direction (often the composite length) and a windowing angle that will capture the desired data pairs.
We recommend that assessments be made on a copy of the variogram or domained estimator. If adjustments are made to a variogram model in a domained estimation object that is being evaluated, any changes made will result in changes to the downstream model.
2. Compare block model evaluations before and after modification
If you decide that modifications to minor axis ranges are required, we suggest that you compare block model evaluations before and after making any adjustments.
This can be done in either an existing Geo/Edge project or after a project has been upgraded to the point release version.
Our suggested workflow for comparison using the point release version is:
1. Open a copy of the project in the point release version (Geo 6.0.5)
2. Copy domained estimation objects containing variogram models with a westerly Dip Azimuth (181->359) and rename with a recognizable suffix.
3. Open the variogram model(s) in the copied domain:
a. Review minor axis calculation parameters (lag, angular tolerance)
b. Review fit of model
c. Adjust as required
4. Copy Combined Estimators and substitute any modified domained estimation objects
5. Make a copy of any block models
a. Substitute any modified Estimation objects or Combined estimators
b. Check calculations, and modify as needed to point at the correct objects
6. Generate comparative statistics:
a. Scatter plots of original and modified evaluations.
b. Univariate statistics of original and modified evaluations
7. Compare Edge summary Resource reports between original and upgrade copy.
Does the update result in forced changes to resource model outputs?
No. If you open an existing variogram window in the Edge version 4.0.5, the experimental variogram in the minor axis direction will change for any west-dipping variograms. But no change will occur to the variogram model or to estimation outputs until you make a deliberate decision to modify the variogram model and save the changes.
What are the options to upgrade?
- Visit MySeequent to download the Leapfrog Edge 4.0.5 software update (using the Leapfrog Geo 6.0.5 installer).
- If you are not able to apply the software update, either because you are using an earlier version of Leapfrog Geo / Edge, or because your internal IT processes preclude you from applying the software update immediately, there are two alternatives as described below:
a.You can continue using your existing version and use ‘custom variograms’ in place of minor axis variograms, to ensure that the models you fit to the minor axis direction are appropriate. In this case you will need to fully understand the nature of the issue, and how use of ‘custom variograms’ can mitigate it.
b. Contact us for support
Contact our Technical Support team at [email protected]