Calculate Variogram

This command takes the selected drillholes and calculates the variogram data, outputting the Nugget, Sill and Range. These parameters are entered into the Carlson Kriging dialogs for gridding and block modeling. Variograms may be 2D or 3D. When the command is first activated, you will be prompted to select the variogram type, as shown below.  Selecting Load Variogram3D point file will skip the drilhole, Strata/Bed, and attribute selection steps, and load a "DAT" point file directly and go into the 3D variogram dialogue.

After selecting the variogram type, you will be prompted to select the drillholes, channel samples, and strata polylines to use for variogram calculation. You will then be prompted to select a strata to process, as shown below.

After selecting the strata to process, you will be prompted to select a value or values to process, as shown below.

2D Variogram

The 2D variogram window is shown below.

Drilling Data:

This section covers the base data points and attributes which are being used in the analysis.

• Head Variable: Lists the variable that is analyzed.
• Tail Variable: Lists secondary the variable that is analyzed for Cross Semivariogram and Correlogram.
  
• Ignore Zeros: Ignores any zero values in the drilling.
  
• Validate Drilling: Lists the number of holes used.
  
• Min/Max/Average: Lists the minimum, maximum and average values of the sample points.
  
• Low and High Trimming Limit: Trimming limits will provide a range selection to process. A value of 0 trimming will delete null values.
• Drilling Paired Dist.: This shows the number of found pairs in the drillholes.
  
• Min/Max/Avg: This is the distance between all sampled pairs of drillholes.
• Output Points: Outputs a ".csv" file of the points in the analysis for verification and further analysis..

Measurement Options:

This bottom left section of the dialogue covers the several options for the measured variogram

The type of Variogram Type button is a dropdown with the following options.

• Semivariogram
• Cross Semivariogram
• Correlogram
• General Relative Semivariogram
• Parwise Relative Semivariogram
• Semivariogram of Logarithms
• Semirodogram
• Seminadogram
  

Variogram Measurement Attributes:

Fitting:
Omni-Directional: Click Exponential option beside big circle on the right to begin. Left click left mouse and drag on the plot to set Range, Sill and Nugget or enter them in the boxes to update the curve. To move the Nugget, left click on the far left side, at the beginning of the curve.

Directional Trend: The variogram plots redraw by clicking on the lines on the large directional window at the top, with the green line, so the 4 angles would be: 0 Azimuth, 135 Azimuth, 90 azimuth and 45 azimuth. The resulting values are displayed above for geostatistical modeling.

The nugget, sill and range are labeled here, for a spherical model:

3D Kriging

The 3D variogram is shown below.  It calculates a 3D ellipsoid of anisotropy which is used in 3d Kriging by following the steps in "Ellipsoid Finder Instructions Tab".

• Loaded File: Informs user the file which has been loaded or whether using the selected data from CAD.
  
• Points in File: The number of data points in the file.  Each point does not hold all of the selected attributes.
• Active Points: The number of data points which have both the head and tail variable.
• Closest Pairs: Gives data on each points closest neighbor.  This information helps select the lag distance and decide whether compositing is necessary
  
• Spatial Analysis: This button will scan the sample data and generate summary values which are used to selected values for the Experimental Variogram.
• Low Trimming Limit: This value sets the minimum attribute value to consider for the variogram.
• Maximum Trimming Limit: This value sets the maximum attribute value to consider for the variogram.
• Head Variable: This is the active value for all variogram types, and it can be changed
  
• Tail Variable: This second variable used in Correlogram and Cross Semivariogram analysis
  

The following items are utility for saving, loading, and manipulating the input data points

• Output CSV Point File: Gives data on each points closest neighbor.  This information helps select the lag distance and decide whether compositing is necessary
  
• Output DAT Point File: This button will scan the sample data and generate summary values which are used to selected values for the Experimental Variogram.
• Load DAT Point File: This will load a dat file into the model.  Useful for saving work from point compositing.  Only selected Head and Tail variables will be saved
  
• Composite Distance:The distance which points should be combined together.  When compositing points values are averaged together.  Compositing is done by selecting "Composite points Together" button.

Experimental Variogram:
This section deals with specifying the settings which to measure directional variograms and how they should be displayed. 

• Variogram Type: The Variogram types include all of the options of 2D as well as including a plot of the number of pairs.  This isn't a variogram type, but instead a shows the number of pairs used to determine the value of each lag, which makes validating data easier.

• Output Lag Pairs: This will output a csv file with a list of each lag pair and their associated directional variogram information and the data values. 
  
• Output Lag Results: This will output a csv file with the resulting values for each lag bin which can be used to store the results of past experiments.
• Variogram Table: Each row represents a measured variogram with controllable direction and direction measurement tolerances.  How each variogram is displayed can also be controlled with Symbol, Color, and Plot options.

Variogram Fan Settings:
This section deals with laying out a set of variograms in a plane.  The Azimuth and Dip define the first direction of the plane normal and the roll describes the spin of the variogram fan.  It is suggested to try apply the fan with Azimuth at 0, Dip at 90, and Roll at 0 and then vary the Roll values to see the changes in experimental variograms.

Model Ellipsoid items deal with fitting a model variogram, and the three directional variograms needed for a 3d Kriging. 

Experimental Variograms are not automatically updated for each change in the Variogram Fan Settings.  This can allow for custom settings per Experimental Variogram.  Select "Apply Fan" to apply to create a set of Experimental Variograms according the the Variogram Fan settings.

The Variogram Fan Settings and Experimental variogram directions are automatically set during the Ellipsoid finder steps, so no further adjustments beyond lag distance settings or direction interval are recommended.

Variogram Fitting:
This section deals with displaying the results of Experimental Variograms and creating the model variograms which are used by 3D Kriging.

The display parameters can refresh for the graph to show adjustments in experimental variogram and adjust which experimental variograms are being displayed.

The Model ellipsoid section deals with setting the values of the modeled variogram and each item is described below

• Select Display Models: Specify which or none of the model variograms are being displayed, only Experimental Variograms 1, 2, 3 can be modeled and they are associated with the Major, Minor, and Intermediate Axis of Anisotropy respectively
• Auto Fit Axes: This will automatically set the nugget, sill and and ranges for all 3 axes according to a single structure model.  This uses a max variography point fitting technique, final judgement and adjustment according to statistical judgement is recommended.
• Number of Structures: The number of unique variography regions.  Each structure is associated with one row of the Model Ellipsoid table
• Total Sill: The sum total of each structure's sill and the nugget effect
• Nugget Effect:  The expected variation at zero distance, a stand in for the inherent variation of the rock mass
• Range: The distance at which the model variogram reaches the specified sill value
• Angle: These describe the orientation of the Model Ellipsoid.  Angle 1 describes the Azimuth, Angle 2 describes the dip, and Angle3 describes the roll.  These values do not affect the plot of the model ellipsoid, but the Kriging analysis.  It is not suggest to change them once set by the Ellipsoid Finder
  

Fan View:
This section deals with visualizing the variography in 3D and 2D plot forms to assist in the selection of minimum or maximum directional variance.  Following the steps

Fan View:
This section deals with visualizing the variography and selecting the minimum or maximum directional variance for the Ellipsoid Finder.  The Variogram Fan 3D view shows the variography in the z axis, along the variogram fan the X, Y axis.  The adjustable plane is the indicator of the selected direction.  The "Variogram Gamma Distance Plot" is the same plot which is in Variogram Fitting but with all of the variograms showing.  The selected variogram is labeled and  shown in blue.

Selecting the rotational arrows switches the target Experimental variogram.  Selecting the left right arrows applies the selected variogram direction, updates the Variogram Fan and Experimental Variograms.

Pulldown Menu Location: StrataCalc
Keyboard Command: vgramrun