Hello Ismail -
The way I explain it is that the test patterns represent typical CD situations that customers may use for their actual designs. The OPC is done on localized grid analysis, so the larger design in general doesn't matter as much as the interaction configurations between polygons within the scope of the grid. Calibre WORKbench has utilities that allow you to customize a test pattern if the standard one does not meet your needs.
If you are simply performing OPC on a design and already have models provided for you, you don't need the test patterns - those are generally used by the people writing the OPC rules and developing the process models.
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