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## Removing one quarter of a plot

Figure 17

To remove a quarter of a plot, you need two clipping planes. To remove one quarter of the plot, first remove one half of the plot. Now, enable the second clipping plane and make sure that it has the same origin as the first clipping plane but a different normal. To remove exactly one quarter of the plot, make sure that the normal is perpendicular to plane 1's normal. Also make sure that plane 2's new normal points into the region that was clipped away by plane 1. The two planes, when considered together, remove one quarter of the plot. For an illustration of this, see Figure4-13. In general, the Clip operator removes regions defined by the intersection of the regions removed by each clipping plane. Follow the same procedure with the third clipping plane to remove only one eighth of the plot.