Abstract: A method of determining and correcting for distortions introduced by an imaging tool. The method includes providing an imaging tool having a field of view (FOV), and creating a target pattern containing a regular array of symmetric sub-patterns having locations spanning the FOV. Using the imaging tool, the method then includes measuring relative position of the sub-pattern images at one or more target orientations, determining tool-induced sub-pattern position deviations from designed locations of the sub-patterns, and applying corrections to compensate for an orientation independent component of the sub-pattern position deviations. The target pattern may be mounted on a stage of the measurement tool, created on a mask used in the lithographic process, or created on a wafer being measured by the measuring tool.