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 under the Tie Line Levelling > Levelling Utilities menu.
Interpolate dialog options
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Channel to interpolate
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Name of the channel to interpolate.
Script Parameter: INTERP.IN
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Output interpolated channel
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Output interpolated channel.
Script Parameter: INTERP.OUT
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Interpolation method
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Select the algorithm used to interpolate dummies. The interpolation options are:
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Linear (default)
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Minimum Curvature
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Akima
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Nearest
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Prediction
Script Parameter: INTERP.METHOD
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Maximum gap to interpolate
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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
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Extrapolation at edges
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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
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Maximum extension at edges
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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
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Application Notes
*GX.NET tools are embedded in the geogxnet.dll file located in the \Geosoft\Desktop Applications\bin folder. To run this GX interactively (outside the menu), first navigate to the bin directory and provide the GX.NET tool in the required format. See the topic for more guidance.
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 cause undesirable overshoot in some areas, whereas Akima interpolation tends to be less smooth but does not suffer from excessive overshoot.
Prediction applies a maximum entropy prediction algorithm to estimate missing values with similar noise characteristics. Useful for FFT filtering. You can enforce continuity and periodicity at line ends.
Linear is a standard straight-line interpolation between points. Nearest assigns the value of the nearest non-dummy point.
