General Radially Symmetric (GNRL)

Use the General Radially Symmetric option to apply a general radially symmetric filter.

General Radially Symmetric Filter dialog options

Filter file name

The format of the filter file is described below. The default file extension is flt.

Application Notes

The general filter is used when you intend to apply a special purpose filter to the data. Normally, filter coefficients are between 0 and 1.The filter coefficients must be defined at discrete wavenumber increments. The first value of the filter file is the wavenumber increment, followed by the coefficients. You are limited to specifying a wavenumber in the filter file that is less than the Nyquist wavenumber, defined as (1/ (2* grid cell dimension)), since the radial spectrum display will only permit you to display wavelengths greater than the Nyquist sampling interval. Assuming that the increment is k, the filter file will be defined as:

GNRL K, I₀, I₁, I₂ etc...

Where:

K the wavenumber increment that should be less than the Nyquist wavenumber.

l_i the filter coefficients at each multiple of K starting at zero . The last filter coefficient is used for all higher wavenumbers. More than one line can be used to give the coefficients. A slash character (/) must follow the last coefficient.

For example, the following defines a low-pass filter that starts at a wavenumber of 0.003 and rolls off to remove all wavenumbers above 0.007:

L(0) = 1

L(0.001) = 1

L(0.002) = 1

L(0.003) = 1

L(0.004) = 0.8

L(0.005) = 0.5

L(0.006) = 0.2

L(0.007) = 0

The syntax of this filter file is:

GNRL 0.001 1. 1. 1. 1. .8 .5 .2 0 /

Ground_unit is the survey ground units as defined in your grid (e.g. metre or feet). Ground units may be left undefined.