Apply Single FFT Filter

Use the Apply Single FFT Filter option (geogxnet.dll(Geosoft.GX.FFT1D.FFT1DFiltering;RunGravityFilters)*) from the menu Moving Platform Gravity > Filters to apply a single 1D Fast-Fourier Transform filter to a channel.

Apply Single FFT Filter dialog options

Channel to filter	Name of the input channel to filter. Script Parameter: FFT1MULT.IN
Output channel	Name of the output channel (created if does not exist). Script Parameter: FFT1MULT.OUT
Filter to apply	Select the filter name to apply. The selected filter's parameters will be displayed below. The filter parameters displayed will be different depending on the filter selected. The following filters can be selected: Apparent density calculation Apparent susceptibility calculation Band-pass Butterworth Continuation Cosine roll-off Gaussian Horizontal derivative Horizontal integration High-pass Low-pass Reduce to magnetic pole Resistance capacitance Vertical derivative Vertical integration Script Parameter: FFT1MULT.FILTER
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Distance increment	Specify the distance increment in ground units. If not specified, the nominal data spacing will be used. Script Parameter: FFT1MULT.SAMPINCR
Interpolation method	Select the Interpolation method to be used as, Minimum Curvature, Linear, or Akima. Script Parameter: FFT1MULT.METHOD

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.

The dialog enables a single filter to be applied to a channel with a single process, in which, the data first gets Fourier Transformed (FT) to the wavenumber domain, then the filter is applied, and the data finally are Inverse Fourier Transformed (IFT) back to the space domain.

The FFT sampling parameters (Distance increment and Interpolation method) ensure that the input data is appropriately sampled for 1D FFT. If your data has a variable spacing between samples (such as may occur in ground-based surveys) then the default Minimum Curvature interpolation method may result in the introduction of artifacts into the filtered output. If this occurs, changing the interpolation method to "Linear", or specifying a distance increment that is appropriate to your data will likely prevent those artifacts from occurring.

The relevant parameters for the selected filter will be displayed, prompting you to enter the values.

Finding Help for a Specific Filter

Once you have selected your filter in the Apply Single Filter dialog, click the Help button and the information for your selected filter will be displayed. You can also click the filter links below.