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