Calculate Residuals

Function

This command measures the accuracy of the strata grid model based on the residual at each drillhole data point. The residual is calculated by removing the data point and then comparing the grid model calculation at the point with the actual value. Residuals for any strata data value such as thickness, elevation or BTU can be calculated using any modeling method including triangulation, polynomial, Kriging, least squares and inverse distance.

Consider calculating residuals for thickness with five drillholes. For each drillhole, the drillhole is temporarily removed from the model and the thickness calculated at the drillhole position. For example, one drillhole could have a thickness of 5.0. When this drillhole is removed and the four remaining drillhole using inverse distance calculate the thickness at this point, the modeled value could be 5.25. The difference of 0.25 between the actual value 5.0 and the modeled value 5.25, is the residual.

The first dialog to appear contains some settings on the residual analysis.

• Ignore Zero Data Values: This will ignore any values of 0 that are found in the drillhole. They could be thickness, elevation or any quality attributes. Sometimes they should not be ignored, depending on what is being modeled.
• Use Report Formatter: Turn this option on to see the report with the Report Formatter. If it is off, then the standard report viewer is used.
• Calculate Histogram: The Histogram is a statistical graph of the distribution of a dataset. It shows the number of data samples within a series of value ranges.
• Number of Histogram Bins: The user can set the number of bins for the graph. For example, if a dataset of sulfur has values from 1.0 to 4.0 and the user asks for 3 bins, then the histogram will show the number of samples between 1.0 to 2.0, between 2.0 to 3.0 and between 3.0 to 4.0.
• Mark Outliers: The Mark Outliers option highlights data points that are more than 2 standard deviations from the data set average. This can be useful for flagging possible problem data points.
• Mark Layer: This is the AutoCAD layer of the circle mark drawn around the outlier drillholes.
• Mark Size: This is the size of the mark, or circle drawn around the outlier drillholes.

For triangulation and polynomial, the residual is not calculated for some points because removing these points shrinks the triangulation area and the point may fall outside the area. Also you need more than three points to calculate residuals with triangulation and polynomial methods.

Prompts

Pulldown Menu Location: StrataCalc in Advanced Mining
Keyboard Command: residuals
File Name: \lsp\makegrid.arx