Extend Threshold Filter to support IsoVolumes.
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
The threshold filter allows thresholding by cell or point data. When thresholding by point-data, it should show a combo-box allowing the user to pick how a cell is selected to be passed through the filter. The options in this combo-box will be something as "all points match", "any point matches", "clip cell".
If "clip cell" is true, then the filter should internally create two "Clip" filters acting as clip-by-scalar. The filter should be smart enough to not create the second clip if it's unnecessary.