Estimate grid values by kriging
This function allows you to fill the Grid Model by kriging interpolations. This function estimates values based on the weighted values of data points closest to the grid point. The weighting is the result of kriging the data points to provide the best linear unbiased estimator.
To run this function: Choose Surfaces > Contouring > Estimate grid values > By kriging, or...
Before using this function you must have already developed an acceptable variogram. This is essential since without these parameters the results of the function will be meaningless.
A 2 dimensional ellipse may be used in the estimation process.
The source of the sample data must be from a string file.
You may interpolate either z values or a numeric value form one of the string file D fields (eg gold grade, silver grade).
You may define spatial constraints (eg inside a closed string, above a certain y value etc), to either:
(a) Select a subregion of the sample data to use to fill the grid in this particular pass; or
(b) Select a subregion of the grid to be filled by the sample data in this particular pass.
You will find that by using the spatial constraints and the facility to fill the Grid Model in multiple passes that you can have great flexiblity in modelling complex surfaces, in particular surfaces containing faults.
From the Contouring menu, select Estimated grid values, then By kriging to invoke the function.
Choose Cancel on the SELECT STRING FILE SOURCE form to return to the GRID menu or Apply to display the SEARCH PARAMETERS form.
Choose Cancel on the SEARCH PARAMETERS form to return to the SELECT STRING FILE SOURCE form or Apply to display the KRIGING PARAMETERS form.
VARIOGRAM
File name
Enter the file name containing the variogram model parameters to use. After a value is selected and focus is moved to another field on this form, the file will be read and the variogram model parameters will be populated into the variogram parameter fields. These fields can be modified if necessary before applying the form. Leave this field blank if the variogram model parameters to use have not been saved to a file.
Model
Enter the model which is to be used for the kriging. This may be SPHERICAL or EXPONENTIAL.
Nugget
This is the nugget value for the model.
You may enter up to 5 structures for the model. A Sill and a Range is required for each structure.
Sill
This is the sill for this structure.
Range
This is the range for this structure.
Constrain interpolation?
Enter N if you wish to fill the whole grid. Enter Y if you wish to define spatial constraints, eg inside string or above a certain x value, to define a subregion of the grid to be filled in this pass.
Enter Y in the Constrain interpolation? field to display the ENTER CONSTRAINTS form.
Choose Cancel on the KRIGING PARAMETERS form to return to the SEARCH PARAMETERS form or Apply to display a progress feedback bar while the interpolations are performed.
Result
Once the calculations are completed the current grid is displayed on the screen as point markers in the graphics layer grid_display. The layer grid_display can be saved to a string file using the SAVE FILE button on the GRID menu. You can also toggle its display using the LAYERS Status button on the GRID menu.