Very often the Gerber data for an entire board or panel is more than we wish to deal with. GBRUnion can crop out a rectangular or polygonal window while performing the Boolean Union operation. This is accomplished by using GBRVU to select either a rectangular region or a polygonal region. GBRVU can also be used to define multiple regions to select. The command line version of GBRUnion (gbrrunmgr) can also do this via the -window: argument.
In the example below we have a 6 x 6 array of IC packages. We need to analyze this circuit but don't need the entire array. By zooming into one of the circuits in GBRVU and specifying a data window that includes only that circuit one can "extract" just the data for a single circuit.
The black outline shows the circuit to be cropped out.
Using GBRUnion's window dialog we specified a selection window of (43.76,2.7) to (57.2,17.7) which exactly grabs one circuit. The entire Boolean process takes only 5-10 seconds on a fast PC. The results are shown below: