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You have a number of choices for entering spectral domain parameters the pass filters. These include frequency, wavelength and distance unit multiples (see Frequency, wavelength and distance unit multiples) and alternatives for geodetic grids:
- You can enter parameters as frequency or wavelength. See Frequency or wavelength units.
- For projected grids, you can enter distances in single or x 1000 multiple units. See Distance unit multiples x 1 and x 1000.
- For geodetic grids you can enter distances in metres or degrees.
Each time you enter a value, INTREPID checks that it is between the Fundamental and Nyquist value for the dataset (See Fundamental and Nyquist Frequencies of the Input Grid).
The following diagram shows the possible views of the Low Pass properties
If your input grid is geodetic, GridFFT displays option buttons for you to choose metres or degrees. Specify the unit you require, then use that unit to enter the parameter values. If you specify a value then select the other option button, INTREPID automatically converts and displays the value in the new unit, using Robin's formula. This conversion between metres and degrees is an approximation. INTREPID bases it on the mid-latitude of the grid.