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# Step 7

Next create a masking filter by selecting MaskPoints from then VTK -> Filters menu. Set the OnRatio to 40. This is the ratio of the points retained: 1 out of every 40 points will be retained. Turn on random point selection by clicking on the Random checkbox. Click Accept. Note that the outline of the solution domain might disappear as a result of this action. You can turn it back on by going back to the Plot3D source (click on Plot3D1 in the Navigation window, switch to the display notebook and check the visibility option). Now, create a glyph filter. This time, change the "Scale Mode" to Vector so that glyphs are scaled by the magnitude of the vectors. Reduce the Scale Factor to 0.005 (otherwise the arrows will be very large) and click Accept.

Note that since the problem geometry is represented by a structured grid, it is possible to sub-sample the points in a more appropriate way. You can use a structured grid extraction filter ( ExtactGrid filter from VTK -> Filters -available only when a structured grid source is active- ) instead of masking points randomly. The extraction filter allows you sub-sample the grid by setting sampling rates in x, y and z directions. The following image was obtained by using an ExtractGrid filter with a VOI (volume of interest) of ((4,55), (3,31), (3,23)) and sampling rate of (3,3,3).

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Last modified: Mon Dec 3 11:01:46 EST 2001