Computing Standard Deviations of Grid Values

RockWorks | Utilities | Grid | Statistics | Standardize

This program is used to re-compute the grid node values such that they represent the standard deviations from the mean. When examining the new model, node values between zero and 1 can be considered background. Values between 1 and 2 can be considered slightly anomalous. Values between 2 and 3 are moderately anomalous. Values between 3 and 4 are strongly anomalous. Values above 4 are extremely anomalous.  When comparing different types of geochemistry (e.g. PCB's vs TDS) , it is often useful to standardize the models first and then divide them by each other.

This tool requires that a real number RockWorks grid model (.RwGrd file) already exists.

Menu Options
Step-by-Step Summary

Menu Options

• Input Model:  Click to browse for the name of an existing grid model (.RwGrd file) to be analyzed.
• Output Model: Click here to type in the name to assign to the new grid file that the program will create, which results from the node-standardizing operation
• Compute Absolute Values: Insert a check here to store the computed standard deviations as their absolute values (e.g. positive). This can be helpful if you wish to view anomalies in general.  This should be left un-checked if it's important to know whether the values are above or below the mean.
• Set Background Values to Zero: Insert a check here to filter out non-anomalous values.
  • Background Threshold:  Click here to enter the standard deviation to be considered background and set to zero.  For example, if your analysis would not consider standard deviations less than "1.0", then you can set this as the threshold.  In this example, this filter would set standardized node values less than 1.0 to 0 in the output model.
• Create 2-Dimensional Grid Diagram: Insert a check in this check-box if you want to display the output grid as a 2D map at this time.  Expand this heading to set up the 2D map layers (bitmap, symbols, labels, line contours, color-filled contours, labeled cells, and/or map border).
• Create 3-Dimensional Grid Diagram: Insert a check in this check-box if you want to display the output grid as a 3D surface.  Expand this heading to set up the 3D map layers (flat surface, Boolean colors, perimeter, reference cage).  You can request both a 2D and 3D representation of the grid model.
• Create Grid Statistics Report: Insert a check here if you want to see a report summarizing the output grid. 
  • Include Standard Deviation:  Check this box if you want the report to include standard deviation.
  • Include Directional Analysis:  Check this box to include slope, aspect, and strike computations. Be warned that these can take a few moments for large grid models.

Step-by-Step Summary

1. Access the RockWorks Utilities program tab. It is not necessary to enter data into the main datasheet because RockWorks will not be creating a new model.
2. Select the Grid | Statistics | Standardize menu option. 
3. Enter the requested menu settings, described above. 
4. Click the Process button to continue.

The program will load the input grid file, compute the mean of the node values, and calculate the deviation of each grid node value relative to the mean, both above and below.  In the output file, a "standardized" value of "2" for a node indicates that the node is 2 standard deviations above the mean. A node value of "-0.579" indicates that the node is 0.579 standard deviations below the mean. If you have requested, negative values will be stored as positives.  In addition, if you have activated the background filter, the program will reset those values to zero.  These standard deviation values will be stored in a new grid file on disk under the output file name you selected.  The requested diagram(s) will be displayed in a RockPlot2D tab and/or RockPlot3D tab in the Options window.   If you requested a statistics report, it will be displayed in a Text Tab in the Options window.

5. You can adjust any of the settings in the Options window and then click the Process button again to regenerate the diagram(s).
   ! Each time you click the Process button, the existing display(s) will be replaced. 
    
6. If you have requested a map, it will be displayed in a RockPlot window. View / save / manipulate / print / export the map in the RockPlot2D or RockPlot3D window.
   
   

See also

• Multivariate Anomalies for information about analyzing multiple grid files at once for anomalous regions.
  

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