The IML graphics subsystem does not automatically clip the output to the viewport. Thus, it is possible that data are graphed outside the defined viewport. This happens when there are data points lying outside the defined window. For instance, if you specify a window to be a subset of the world, then there will be data lying outside the window and these points will be graphed outside the viewport. This is usually not what you want. To clean up such graphs, you either delete the points you do not want to graph or clip the graph.

There are two ways to clip a graph. You can use the RESET CLIP command, which clips outside a viewport. The CLIP option remains in effect until you submit a RESET NOCLIP command. You can also use the GBLKVP command, which clips either inside or outside a viewport. Use the GBLKVP command to define a blanking area in which nothing can be drawn until the blanking area is released. Use the GBLKVPD command to release the blanking area.