Interpolate

Use the Database Tools > Channel Tools > Interpolate menu option (geogxnet.dll(Geosoft.GX.Database.InterpolateChannel;Run)*) to replace dummies in a channel, while honouring a minimum gap.

The option is also available with the Geophysics Levelling extension under the Tie Line Levelling > Interpolate menu.

Interpolate dialog options

Channel to interpolate

Name of the channel to interpolate.

Script Parameter: INTERP.IN

Output interpolated channel

Output interpolated channel.

Script Parameter: INTERP.OUT

Interpolation method

Select the algorithm used to interpolate dummies. The options are: Linear(default), Minimum Curvature, Akima, Nearest or Prediction interpolation.

Script Parameter: INTERP.METHOD

Maximum gap to interpolate

By default, this entry is blank, indicating that all gaps are to be interpolated. If you intend to skip gaps wider than a certain number of points, enter the specific number of points. The gap value is the actual distance between data points, so it is one more than the number of dummies to interpolate. This means 2 is the minimum value of significance.

Script Parameter: INTERP.GAP

Extrapolation at edges

Edge is defined as where a data value is beside a dummy, not just at the beginning and end of a line. Accordingly, edges extend into internal gaps as well as the ends. The choices are None (default), Same (as the interpolation method), Linear, Nearest. If the Prediction interpolation method has been chosen, the Periodic extrapolation method is offered. This fulfills the FFT filtering requirement.

Script Parameter: INTERP.EDGE

Maximum extension at edges

This entry item is disabled if the edge method is set to None . The minimum edge value is 1 (if you do not want edges at all, use the None option, rather than Zero.)

You have the option of leaving it blank with the result that all gaps would be filled across, nullifying the gap value.

To fully extrapolate to the ends beyond the data, set the edge method to any but the None option and clear the edge items value.

Script Parameter: INTERP.EXTEND

Application Notes

*The GX tool will search in the "...\Geosoft\Desktop Applications \gx" folder. The GX.Net tools, however, are embedded in the geogxnet.dll located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" folder, then supply the GX.Net tool in the specified format.

Both 'Minimum curvature' and Akima interpolation methods define a second-order cubic spline to interpolate dummy values. 'Minimum curvature' produces the smoothest possible interpolation, but may create undesirable over-shoot in some areas, while Akima interpolation tends to be less smooth, but does not suffer from unreasonable over-shoot. 'Prediction' uses a maximum entropy prediction algorithm to predict the missing values such that they will have noise characteristics similar to the original data; when choosing this option, you can force the two ends of each line to be continuous and maintain periodicity. This is specifically needed for applying FFT filters. 'Linear' is a standard straight-line technique, and 'Nearest' assigns the value of the nearest non-dummy point.